Survival of Escherichia coli in the environment

Survival of Escherichia coli in the environment:
fundamental and public health aspects
Jan Dirk van Elsas1
, Alexander V Semenov1
, Rodrigo Costa2 and Jack T Trevors3
Department of Microbial Ecology, Centre for Ecological and Evolutionary Studies, University of Groningen,
Haren, The Netherlands; 2
Microbial Ecology and Evolution Laboratory, Centre of Marine Sciences (CCMar),
Algarve University, Faro, Portugal and 3
Department of Environmental Biology, School of Environmental
Sciences, University of Guelph, Guelph, Ontario, Canada
In this review, our current understanding of the species Escherichia coli and its persistence in the
open environment is examined. E. coli consists of six different subgroups, which are separable by
genomic analyses. Strains within each subgroup occupy various ecological niches, and can be
broadly characterized by either commensalistic or different pathogenic behaviour. In relevant cases,
genomic islands can be pinpointed that underpin the behaviour. Thus, genomic islands of, on
the one hand, broad environmental significance, and, on the other hand, virulence, are highlighted in
the context of E. coli survival in its niches. A focus is further placed on experimental studies on
the survival of the different types of E. coli in soil, manure and water. Overall, the data suggest that
E. coli can persist, for varying periods of time, in such terrestrial and aquatic habitats. In particular,
the considerable persistence of the pathogenic E. coli O157:H7 is of importance, as its acid
tolerance may be expected to confer a fitness asset in the more acidic environments. In this context,
the extent to which E. coli interacts with its human/animal host and the organism’s survivability in
natural environments are compared. In addition, the effect of the diversity and community structure
of the indigenous microbiota on the fate of invading E. coli populations in the open environment is
discussed. Such a relationship is of importance to our knowledge of both public and environmental
The ISME Journal (2011) 5, 173–183; doi:10.1038/ismej.2010.80; published online 24 June 2010
Keywords: soil; ecology; E. coli; environment; molecular methods; pathogen; public health; survival
Escherichia coli occurs in diverse forms in nature,
ranging from commensal strains to those pathogenic
on human or animal hosts. On the basis of genomic
information, the species has been divided into six
(five major) different phylogenetic groups, denoted
as A, B1, B2, C, D and E (Touchon et al., 2009).
These subgroups encompass saprophytic (A) and
pathogenic (in particular B2, D) types and are
often considered to be the result of long (41 Myr)
evolution time. Although the physiology, genetics
and biochemistry of E. coli have been intensively
studied, it is not known in detail how the bacterium
behaves in its natural habitats. Such habitats have
been divided in primary, that is, animal/human
host-associated (MacFarlane and MacFarlane, 1997),
and secondary (that is, open or non-host-associated)
habitats (Savageau, 1983). The versatile behaviour
exhibited by E. coli in these habitats is reflected
in the immense diversity within the species
(Bergthorsson and Ochman 1998). In fact, the
various commensal and pathogenic forms of E. coli
are known to possess genomes that may differ by up
to 20% (Ochman and Jones, 2000). The phenotypes
of the different E. coli forms are related to such genomic differences and the ensuing patterns of gene
expression. The occurrence of key genomic islands
in E. coli that define the different behavioural types
is clearly an underpinning factor (Dobrindt et al.,
2004; Touchon et al., 2009).
The commensal form of E. coli, exemplified by
strain MG1655 (Touchon et al., 2009), is traditionally considered as a harmless bacterium that lives in
the intestinal system of mammals and assists its host
in the breakdown of particular carbon compounds.
On the other hand, the pathogenic forms of E. coli,
such as the verotoxigenic (VTEC) (Taylor, 2008),
enterohaemorrhagic (EHEC, a subclass of the VTEC
class), enteroinvasive (EIEC) and uropathogenic/
extraintestinal pathogenic (UPEC/ExPEC) classes,
all possess capacities that are harmful to their hosts.
The well-known E. coli O157:H7 is an example of a
harmful VTEC, which has already caused mortality
worldwide. VTEC strains are capable of producing
verotoxins (genes denoted as stx) (Taylor, 2008)
Correspondence: JD van Elsas, Department of Microbial Ecology,
Centre for Ecological and Evolutionary Studies, University
of Groningen, Kerklaan 30, Haren, Groningen, 9750RA,
The Netherlands.
E-mail: [email protected]
The ISME Journal (2011) 5, 173–183
& 2011 International Society for Microbial Ecology All rights reserved 1751-7362/11
causing mild to bloody diarrhoea, which eventually
culminates in the haemolytic uraemic syndrome.
More than 150 serotypes of verotoxin-producing
E. coli have been found, but the majority of
outbreaks are related to serotype O157. E. coli
O157:H7 is dangerous because of its resistance to
low pH (B2.5), which allows passage through the
stomach, its low infective dose (as few as 10 cells)
and its high pathogenicity (Tilden et al., 1996).
Following tissue invasion, it may even cause death
(Ritchie et al., 2003). Moreover, the stx genes were
found to be transferable to non-pathogenic E. coli
strains, allowing these to enhance their virulence
(Herold et al., 2004).
In the light of current questions concerning
the genomic makeup, origin and environmental
circulation of—in particular—pathogenic E. coli,
this review will examine our current knowledge of
the fate of different E. coli forms in open environments, with a focus on E. coli O157:H7. We will
emphasize, whenever possible, the impact of the
genomic makeup of the organism.
Importance of genomic islands
All pathogenic strains of E. coli contain genomic
regions (islands) loaded with a suite of virulence
genes that encode key traits for adherence/colonization, invasion, secretion of toxic compounds and
transport functions, as well as siderophore production (Touchon et al., 2009). Some of these capacities
are also present in commensal E. coli strains and
may enhance environmental fitness, although this is
often not recognized. A full complement of islandborne traits, which together define behaviour, is
often required for pathogenicity (Touchon et al.,
2009). With a basis in recent genome-sequencing
projects, the diversity across E. coli genomes is now
better understood than ever before (Kudva et al.,
2002; Touchon et al., 2009). It is clear that, in
particular, horizontal gene transfers have been
involved in the spread of the virulence-related
genomic islands across different E. coli strains
(Ochman and Jones, 2000; Touchon et al., 2009).
Thus, the picture of an about 2000-gene core genome
characteristic for the species, in addition to an open
pan genome (currently about 18 000 genes), has
recently emerged (Touchon et al., 2009), illustrating
the great impact of horizontal gene transfer for genomic plasticity of the species (Figure 1). An analysis
of the sites where insertions or deletions had
preferentially occurred across all E. coli genomes
recently identified 133 such hotspots (Touchon
et al., 2009). Figure 2a illustrates a hypothetical
display of such sites across the genomes of
Pan genome
Average E. coli genome
~ 11%
~ 26%
~ 62% Evolutionary
~2000 genes ~18000 genes
Core Genome
~4700 genes
Gene Loss
Gene acquisition
Gene Maintenance
Adaptive response?
Gene persistence Gene volatility
Phylogenetic signatures
and genomic islands
Adaptive metabolism Strain specificity
IS elements
Phage-like elements
Differential nucleotide usage
House-keeping functions Unknown functions Stress tolerance
Environmental hardiness
Metabolic versatility
Figure 1 The average E. coli genome is shaped by a multitude of evolutionary forces derived from its primary (host) and secondary
habitats, in which both biotic (predators, competitors, cheaters, host defense mechanisms) and abiotic (pH, temperature, UV, mineral
depletion and so on) pressures are present. E. coli strains possess a core of about 2000 genes, which equip them with a versatile
metabolism. The E. coli pan genome consists of about 18 000 genes, of which 11% belong to the core (dark blue), a large portion (62%,
blue) is composed of so-called ‘persistent’ genes, and 26% can be considered as ‘volatile’ genes (pale blue) (Touchon et al., 2009). Events
of gene acquisition and loss are consistently linked to insertion/deletion hotspots (red), and cooperatively shape the E. coli genome with
selectively maintained core/persistent genes. These events may result in the evolution of gene clusters defining specific E. coli
phenotypes, such as the pap operon, which is involved in the pathogenesis of urinary tract infection caused by UPEC strains (see
Figure 2). The arrow represents a hypothetical gradient in which E. coli genomic features that are most likely associated with volatile,
persistent and core genes are shown.
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JD van Elsas et al
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commensal, EHEC and UPEC strains. One concrete
example, shown in Figure 2b, is offered by the pheV
tRNA hotspot, displaying the different inserts across
strains K-12 MG1655, O157:H7 (Sakai) and CTF073
(Touchon et al., 2009). Strikingly, all the four typical
UPEC/ExPEC strains examined consistently contained a similar insert at this site, which is denoted
as the pap operon. This operon was found to have
a role in E. coli fitness in urinary tract invasion.
Interestingly, some gene modules were common
between the pheV islands of the UPEC strain
CFT073 and strain K12 (Figure 2b). In contrast, the
pheV insertion hotspot in the O157:H7 strain (Sakai)
was composed of 32 strain-specific coding regions
encompassing genes for hypothetical proteins next
to those for putative enterotoxin and cytotoxin.
In spite of the fact that we currently possess such
detailed information about the often substantial
within-E. coli genomic variation, we lack a general
understanding of how the genomic makeup translates into specific behaviour/survival in a complex
open environment. One real possibility is the fact
that we often overlook the environmental relevance
of particular island traits, which are thought of
as being important in the pathogenic process. An
example of this is the mobile iron uptake operon
system ybt, originally denoted as a so-called highpathogenicity island that is often found in E. coli
at asn tRNA insertion sites (Schubert et al., 2004).
An investigation of online genomic data taught us
that this operon was actually spread across the
different E. coli subgroups in both pathogenic and
commensal forms (Figure 3). The operon may be
considered to represent an environmentally relevant
trait that is transferable by horizontal gene transfer
given its occurrence in many species and genera in
the family Enterobacteriaceae (Schubert et al.,
2009). However, we do not know what it adds to
the already substantial iron-scavenging capabilities
of E. coli.
The lifestyle of E. coli is biphasic
Over evolutionary time, the different E. coli
subgroups may have largely experienced biphasic
lifestyles, consisting of host-independent and
host-associated phases. The interactions with the
host may differ in severity in accordance with the
E. coli and host type, and—given the complexity
and interplay of current pathogenicity determinants on the genomic islands—may have evolved
gradually. That is, complexity may have been
progressively added to the gene repertoire involved
in the host-interactive process. For instance, cells of
E. coli that enter the human/animal stomach with
ingested food are confronted with severe stress due
to the often low pH in the intestinal tract. Following
stomach passage, they may then encounter conditions that are amenable to growth and survival in
the intestinal system. In contrast, conditions in the
open environment are very different. Thus, fluctuating but generally low concentrations of available
carbon/energy sources, temperatures, oxic versus
anoxic conditions and variable (low to high) osmolarity will be present. In the light of these challenging conditions, most forms of E. coli seem to have
conserved particular key evolutionary adaptations
in their core genomes, as indicated by the presence
in most strains of import systems, such as siderophore-mediated iron uptake systems (Schubert
et al, 2004) or ABC transporters for uptake of amino
acids and sugars. This suggests a high ability in
E. coli to obtain diverse nutrients, aiding in its
survival in open environments (Ihssen et al., 2007).
It was recently suggested that ‘the more particular
types adapt to hosts in which they find suitable
niches, the more they will lose the ability to grow in
other, contrasting, environments’ (Franz and van
Bruggen, 2008). However, this seems contentious, as
the capability of E. coli to evolve and survive in a
formerly occupied or new habitat may not be easily
lost. Growth efficiency and competitiveness under
conditions of low available nutrient levels likely
Aligned E. coli genomes
0 800 1600
Gene numbers
PheV hotspot
K-12 MG1655
EHEC O157:H7
pap operon
Figure 2 When complete genomes of E. coli strains are aligned,
typical insertion/deletion hotspots can be identified at corresponding locations, as hypothetically displayed in (a). Both the
size and gene composition of these regions may differ widely
between strains, as exemplified in (b) for the pheV tRNA insertion
hotspot. Here, the pheV hotspots of commensal (K-12 MG1655),
enterohaemorrhagic (EHEC, O157:H7 Sakai) and uropathogenic
(UPEC, CTF073) strains are compared after the data of Touchon
et al. (2009). Sections of the insertion hotspots highlighted in
different patterns/colours correspond to distinct gene modules
(see Touchon et al., 2009 for details). The pap operon (red) has a
role in urinary tract infection, is a genomic signature of UPEC/
ExPEC strains and can be found in the pheV insertion hotspots
of strains CFT073, APEC O1, S88, UMN026 and IAI39. Black
sections represent genes/gene modules, which are specific to the
corresponding strains. The pheV insertion hotspot in the O157:H7
strain Sakai is composed of 32 strain-specific CDs encoding,
among others, 22 hypothetical proteins, 4 transposases, 1 putative
enterotoxin and 1 putative cytotoxin. Gene modules highlighted
in green are common to the pheV islands of strains K-12 and
CFT073. Genes in these modules encode, among others, glycolate
oxidases, a glycolate transporter and putative nucleoside triphosphate hydrolases. (A full colour version of this figure is available
at The ISME Journal online).
Survival of E. coli in the environment
JD van Elsas et al
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represent the most important physiological factors
leading to the successful persistence of E. coli in
nutrient-limited open environments (Ihssen and
Egli, 2005). Therefore, it is important to understand
the mechanism(s) of adaptation to nutrient-limited
environments, which affect the survival of E. coli in
such conditions.
E. coli persistence in open environments—importance and threat
The extent to which E. coli, in particular pathogenic
strains, can survive in open environments and
which factors affect this survival rate are crucial
issues from a fundamental point of view. Next to
their capabilities to acquire nutrients, some E. coli
strains produce filamentous structures that extend
from the cell surface and help cells to attach to
surfaces (for example, plant surfaces). Owing to this
ability, E. coli coming from soil, manure, irrigation
water (Solomon et al., 2002) or contaminated seeds
(Itoh et al., 1998) may colonize (and thus find a
refuge niche in) plants such as radish (Itoh et al.,
1998) and lettuce (Solomon et al., 2002). Specifically, E. coli may access roots or leaf surfaces by
splashing during rainfall or irrigation (Natvig et al.,
2002). Internal plant compartments can also be
colonized (Solomon et al., 2002), so that the E. coli
cells cannot be easily washed from plant parts or be
killed and removed by disinfectants and washing.
Thus, from infested consumable products, the
organism can further spread to uncontaminated
products during food processing and packaging,
resulting in dissemination in the food production
chain. Pathogenic E. coli strains such as E. coli
O157:H7 thus pose a threat to the food chain and
represent a still underestimated environmental risk.
It has been estimated that food-borne diseases cause
B76 million illnesses, 325 000 hospitalizations and
5000 deaths each year in the United States (Mead
et al., 2000), and a significant part of the outbreaks
has been attributed to E. coli O157:H7. In Europe,
such infections are also on the rise (Fisher and
Meakins, 2006). Recently, a large multistate outbreak
of E. coli O157:H7 from contaminated fresh spinach
in the United States resulted in 187 cases of illness
(including 97 hospitalizations and three deaths).
E. coli fate in natural habitats
Provided resource availability and key abiotic
conditions are propitious, E. coli populations can
survive and even grow in open environments.
However, under fluctuating environmental conditions, such as those present in many soils and
aquatic environments, growth may be differential
and gross bacterial death may ensue if the death rate
exceeds the growth rate. Both growth and death
rates are determined by the environmental conditions at the local scale and by how the microorganism is able to cope with these local conditions
by regulating its gene expression patterns.
For instance, an elegant study (Tao et al., 1999)
used functional genomics to determine gene expression patterns in E. coli cells grown on a nutrient-rich
versus a minimal medium. All 4290 protein-encoding genes were analyzed through microarray hybridization (RNA extraction followed by construction
of hybridization probes through cDNA synthesis
and hybridization to genomic DNA microarrays).
The study showed that rapidly dividing cells in the
rich growth medium had elevated expression of
genes involved in translation and did not require
int Irp6-9 Irp3-5
Strain Phylotype Lifestyle ybtA iron
O150:H5 SE15
ybtA irp2 irp1 fyuA
K-12 MG1655
Figure 3 Occurrence of the mobile ybt operon encoding the
yersiniabactin (Ybt) iron-acquisition system across E. coli strains
of diverse phylogenetic groups and lifestyles. All strains shown,
with the exception of ECOR 02 and O6:K5:H1 DSM6601, have
their complete genomes sequenced. The island is heavily present
in B2 and D phylotypes. Its occurrence in commensal representatives of the B2 group suggests ecological relevance and, possibly,
acquisition by ancestral B2 types. A role of the ybt operon as a
possible ‘saprophytic island’ can be postulated because of its
wide occurrence in bacteria of divergent lifestyles, including
E. coli strains of phylogenetic groups A, B1, B2, D and E (Hacker
and Carniel, 2001). A general representation of the functional and
‘mobile’ sections of the island is adapted from Schubert et al.
(2004) and shown in the upper panel. asn, asn tRNA gene; int,
integrase-encoding gene. Genes in the functional operon code for
irp, iron-regulated proteins, including irp2 (Ybt peptide synthetase) and irp1 (Ybt peptide/polyketide synthetase); ybtA, AraCtype transcriptional activator; and fyuA, outer membrane protein.
Other genes/gene clusters frequently present in genomic islands
that may enable E. coli strains to thrive in multiple niches or act
as saprophytes, commensals or pathogens are those involved in
multidrug/antibiotic resistance and in the production of adherence factors (reviewed in Hacker and Carniel, 2001).
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JD van Elsas et al
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expression of amino-acid biosynthesis genes in
comparison to cells in the minimal medium. Hence,
the environmental conditions clearly directed the
expression of suites of genes geared toward optimal
growth. Such global gene expression analysis can
be further used to study whole-cell physiology
under diverse conditions, mimicking those deemed
relevant for open environments. In particular, the
dynamics of gene expression in a habitat such as
soil has been underexplored (Saleh-Lakha et al.,
2008). For instance, the gene expression patterns of
different E. coli commensal and pathogenic forms
could be assessed to determine whether particular
genes, including the iron acquisition and other
virulence-related ones, are expressed in this (and
other) environment(s) and to what extent this
expression affects bacterial survival. In this context,
it was found that over 300 strain O157:H7-specific
genes responded to a growth transition in minimal glucose medium (exponential to stationary),
with significant changes in gene expression
including multiple genes in pathogenicity islands
or toxin-converting bacteriophages (Bergholz et al.,
Growth and survival of E. coli in open environments is often restricted by the availability of
nutrients and energy sources. In a growing culture,
starvation will ensue at a given moment due to a
limitation of particular carbon or other substrates.
Under such starvation conditions, the cells progressively metabolize their cellular carbohydrates,
followed by proteins and RNA, while initially
protecting the DNA. In most open environments,
E. coli may behave similarly when nutrients exhaust. However, it will first respond to the different—often complex—energy sources and organic
compounds, which are usually present in low
concentrations. Under such low-nutrient conditions, different alternative catabolic functions and
binding proteins will become derepressed, as found
in cultures under glucose or arabinose limitation
(Ihssen and Egli, 2005). Similarly, iron may become
limiting and thus iron-acquisition operons might
become derepressed. It would thus be interesting to
test the environmental fitness and gene expression
of the iron-acquisition-island-containing strains
(Figure 3). Furthermore, E. coli was also found to
exhibit a high degree of catabolic flexibility, which
conferred a clear fitness advantage in its secondary
habitats such as soil and water (Ihssen and Egli,
2005). E. coli O157:H7 may survive and even grow
in sterile freshwater at low carbon concentrations,
which stands in contrast to the common conception
that the organism will die out over time in such
strongly carbon-limited environments (Vital et al.,
2008). Moreover, because of the production of
RpoS (subunit of RNA polymerase, represents a
major factor involved in starvation survival), E. coli is
able to rapidly adapt to, and tolerate, diverse stress
conditions (Lange and Hengge-Aronis, 1991). It was
thus shown that high osmolarity (Muffler et al.,
1996), extremes and fluctuations of temperature
(Muffler et al., 1997), low pH (Bearson et al., 1996)
and low growth rate (Ihssen and Egli, 2004) induce
rpoS in E. coli cells. Supporting the importance of
rpoS, an rpoS E. coli mutant showed decreased
survival (colony-forming unit counts) in stationary
phase in seawater (Rozen and Belkin, 2001).
Finally, E. coli can enter a ‘dormant’ (previously
denoted as viable but non-culturable) state. In this
state, cells cannot be easily recovered on standard
laboratory media, but are still present as viable cells.
For instance, in an experiment with E. coli O157:H7
in manure, significantly higher numbers of the
organism were found by direct microscopic counts
than by plating on a selective medium (Semenov
et al., 2007). This indicated the prevalence of
‘dormant’ cells in the total E. coli O157:H7 population. The state can be triggered by stress conditions
that are imposed, for instance, by low temperature
(for example, 4 1C) or toxic metals (for example,
copper, lead, mercury and cadmium) (Klein and
Alexander, 1986). Although the resistance to starvation of E. coli leads to its persistence in open
environments, we are unaware of the impact of
cells entering this state, that is, whether it represents
a state of enhanced environmental injury or a true
survival mode.
Factors affecting E. coli fate in open environments
General observations on E. coli survival
E. coli can, to varying extents, survive in different
open environments such as soil, manure and water
(Kudva et al., 1998; Jiang et al., 2002; Vital et al.,
2008). There are also possibilities for migration
between these habitats. For instance, E. coli may
reach the groundwater from top soil layers, as
revealed in several studies (Mankin et al., 2007).
Soil factors such as porosity, surface area, bulk
density and macropore structure have important
roles in the leaching of invading bacteria by their
influence on adsorption and gravitational movement
with water (van Elsas et al., 1991). However, for
organic substrates such as manure and slurry, the
adsorption and desorption behaviour of bacteria is
not only linked to differences in physical characteristics of the substrate, but also to biophysical
properties of the organic matter (Mankin et al., 2007;
Semenov et al., 2009).
As a general observation, the population sizes of
E. coli in soil and soil-related (manure) habitats have
shown progressive declines in all habitats studied.
On the other hand, the fate of E. coli populations
under complex natural conditions is often not accurately predictable (Semenov et al., 2008). Although
the conditions for survival of E. coli in soil, manure
and water are considered to be less favourable than
in the intestinal system (Tauxe et al., 1997), the
organism has been observed to survive for days
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(at physiological (430 1C) temperature, aerobic
and under nutrient-limiting conditions) to almost
a year in the former habitats (Kudva et al., 1998;
Fukushima et al., 1999; Jiang et al., 2002).
It is important to understand the environmental
controls that affect the survival of E. coli in its
secondary habitats (Table 1) (Habteselassie et al.,
2008), as in such habitats, the bacterium will be
faced with conditions such as low or fluctuating
levels of energy sources, high to low levels of
oxygen, fluctuating and often extreme temperatures,
low pH and/or high osmolarity.
Availability of resources
The availability of resources such as carbon substrates probably is the main critical factor that
affects the persistence of E. coli in open environments such as soil and water. The resource availability will relate to the local conditions that typify
the habitat. For a chemoheterotroph such as E. coli,
obtaining sufficient carbon compounds will clearly
impact its chances of survival. Thus, during adaptation to glucose-limited conditions, E. coli cells were
shown to be ‘primed’ for the efficient uptake of
various carbon sources due to the upregulation of a
large number of genes encoding periplasmic binding
proteins (Franchini and Egli, 2006). Such priming
would allow these cells to capture a range of
resources that occur in low concentrations. However, a stronger limitation of resources in environments inhabited or invaded by E. coli will govern its
gene expression in another way, affecting survival.
Nutrient scarcity in water systems as well as
‘oligotrophication’ of farm environments (when
easily available nutrients are in immobilized form)
have been suggested as factors or strategies that
reduce the chances of survival and thus prevalence
of E. coli (for example, strain O157:H7) (Franz and
van Bruggen, 2008). In addition, cells may also enter
a dormant state if particular stressors are present in
the resource-restricted environment (Semenov et al.,
Temperature and temperature regime are other
important factors that influence E. coli survival
and growth. In an animal host body, temperature is
often stable, whereas it may be strongly fluctuating
in a non-host environment such as soil or water.
Until recently, the effect of fluctuating temperature
on E. coli survival and adaptation (compared with
stable temperatures) in soil was poorly understood,
as previous survival experiments had all been
carried out under temperature-stable conditions
(Kudva et al., 1998; Himathongkham et al., 1999;
Franz et al., 2005). Recent results obtained with
E. coli O157:H7 showed that survival in manure
under fluctuating temperatures was generally lower
than that under constant temperature (Semenov
et al., 2007). Moreover, the reduction in survival of
the organism was more pronounced when the
amplitude in the temperature oscillations was larger
(7 1C) than at smaller amplitudes (4 1C). Temperature
increase might constitute greater stress and energy
expenditure for the organism than decrease in
temperature (Semenov et al., 2007). Moreover, gene
expression patterns are probably constantly altered
under temperature fluctuations. It was recently
shown that the histone-like nucleoid structuring
(H-NS) protein in E. coli controls a majority of
Table 1 An overview of survival studies of E. coli
Key factor Influence of the key factor on
Organism Substrate Reference
Temperature Decline rate increases at high
E. coli; E. coli
Manure, soil Himathongkham et al. (1999); Kudva et al.
(1998); Nicholson et al. (2005); Semenov
et al. (2007); Sjogren (1994); Sjogren (1995)
Oxygen Decline rate increases in aerobic
E. coli O157:H7 Manure, soil Fremaux et al. (2007); Kudva et al. (1998)
pH Decline rate increases at high pH E. coli O157:H7 Manure Bach et al. (2005); Buchanan et al. (1993);
Franz et al. (2005); Lin et al. (1996)
Soil texture Decline rate increases at low
level of clay fraction
E. coli; E. coli
Soil Artz et al. (2005); England et al. (1993);
Gagliardi and Karns (2000); Mankin et al.
(2007); Oliver (2007)
organic carbon
Decline rate increases at low
level of DOC
E. coli O157:H7 Soil Franz et al. (2008); Semenov et al. (2008);
Semenov et al. (2009)
Complex, indirect influence E. coli O157:H7 Manure, soil Jiang et al. (2002); Kudva et al. (1998);
Semenov et al. (2007); Unc et al. (2006)
Complex influence E. coli O157:H7 Soil Gagliardi and Karns (2000); Nicholson
et al. (2005); Semenov et al. (2009)
Type cow diet Decline rate increases at low
fiber diet
E. coli O157:H7 Manure Bach et al. (2005); Franz et al. (2005)
Abbreviation: E. coli, Escherichia coli.
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thermoregulated genes at 37 1C and 23 1C (WhiteZiegler and Davis, 2009). Hence, differential gene
regulation in E. coli may occur across a broad
temperature range, next to the regulations occurring
at single temperatures (for example, the optimal
growth temperature). The H-NS protein may provide
a very efficient mechanism of gene expression
control under fluctuating temperatures, but we need
to increase our understanding of the relationships,
if any, to heat and cold shock proteins.
In several experiments, the survival of E. coli in soil
was shown to be related to the local pH, and in
particular soil acidity was detrimental. Expression,
under such conditions, of the alternate sigma factor
rpoS in E. coli was related to the induction of acid
resistance. In particular, E. coli O157:H7 possesses
systems for survival at low pH and therefore can be
considered to be an intrinsically acid-resistant
bacterium (Foster and Spector, 1995; Lin et al.,
1996; Sang et al., 2000). Although E. coli O157:H7
strains still showed different capacities to survive in
acidic environments (Lin et al., 1996), they all were
superior in their survival over non-O157 EHEC
(Bergholz and Whittam, 2007). Variation in rpoS
induction levels might explain the variability in
acid resistance for the different E. coli O157:H7
strains. Although three known acid resistance
mechanisms, that is, two amino acid decarboxylase-dependent systems (glutamate and arginine)
and a glucose catabolite-repressed system, have
been tested (Large et al., 2005), none of these incited
acid resistance in E. coli O157:H7. This suggested
that the organism possibly uses combined mechanisms or even as-yet-unidentified alternative mechanisms. Strikingly, particular E. coli O157:H7
strains almost appeared as acidiphiles, as their
survival was higher at low pH than at relatively
high pH (Franz et al., 2005). However, a significant
variation in the ability to survive in low-pH
environments was found among isolates within a
single serotype (Buchanan and Edelson, 1999).
Availability of water
The availability of water is another key determinant
of E. coli survival and growth. Severe lowering of the
water content (for example, in soil) incites increasing water stress around the cells, whereas water
saturation will rapidly surround cells with water
and induce anoxic conditions. Both extremes have
severe consequences for E. coli physiology and
survival in the system, given that extreme drought
might result in massive cell death, whereas flooding
will shift cellular metabolism to anaerobic processes. However, the behaviour of E. coli in open
environments, in particular how the organism copes
with fluctuations in water availability, is still
Presence and diversity of an indigenous microflora
In all natural habitats, E. coli populations will
interact, in a loose or intricate way, with the local
biota, including the microbial communities. Thus,
different types of interactions can be expected in the
intestinal tract of humans/animals, in manure, soil,
irrigation water and on/in plants. One major microbial factor is the presence of protozoa, which can
have a negative effect on E. coli survival as a result
of predation, but sometimes even enhances survival.
The latter was shown to occur for E. coli O157 in the
environmental protozoan Acanthamoeba polyphaga
(Barker et al., 1999). In contrast, the cumulative
effect of the total indigenous microflora on E. coli
survival is often negative as a result of predation,
substrate competition and antagonism (Jiang et al.,
2002; Unc et al., 2006; Semenov et al., 2007).
Contrary to the declining populations that are
often seen in natural habitats, populations of E. coli
can increase in such substrates under sterile conditions, that is, without predatory, antagonistic or
competing organisms. This indicates that the natural
microbiota in such cases has an overriding effect on
survival (Jiang et al., 2002; Unc et al., 2006;
Semenov et al., 2007). The diversity of the indigenous microbial communities has been brought up as
an important factor that regulates the population
dynamics of invading E. coli (van Elsas et al., 2007).
According to this view, ecosystems with a higher
level of biodiversity (Trevors, 1998) are more
resistant to perturbances than those with a lower
diversity (Tilman, 1997). Consequently, the former
habitats would be less susceptible to invasion by
E. coli than the latter (Girvan et al., 2005; Semenov
et al., 2008). It is an old paradigm that most
ecosystems are microbiostatic, that is, they have
filled ecological niches and are difficult to invade.
Although the exact influence of autochthonous
microbial diversity and community structure on
E. coli survival is still unclear, these two aspects of
the microbiota are considered to be important.
Indeed, the survival in soil of an introduced E. coli
O157:H7 derivative was inversely proportional to
the diversity of the microbial community present,
established through differential fumigation and
regrowth (van Elsas et al., 2007). The progressively
changed microbial diversities and community
compositions coincided with an enhancement of
the survival rate of the invading pathogen. However,
the impact of the indigenous microflora on E. coli
might have been exacerbated, as the nutritional
conditions are remote from those in the natural
reservoir of the organism. To explain the effect, we
hypothesized that lowering of the complexity of the
soil microbiota probably resulted in a reduction of
functional redundancy, which enhances the chances
for the introduced organism to occupy a niche in the
system and persist as a member of the community.
However, we did not examine to what extent
different functional groups in the indigenous microflora affected survival of the invading E. coli. Some
Survival of E. coli in the environment
JD van Elsas et al
The ISME Journal
organisms could be direct competitors by occupying
the same niche, whereas others might have antagonistic or predatory activities. Isolation and identification of microorganisms that promote the decline
of the invader may pinpoint inhibitory species,
which might be applied as probiotics to reduce the
survivability of pathogenic E. coli (Tabe et al., 2008).
Conversely, the presence of cellulose- and lignindegrading organisms might provide E. coli with
easily available carbon sources.
Is there a relationship between E. coli
genotype and survival capability in the
open environment?
E. coli is closely related to Salmonella, with both
species belonging to the same family, the Enterobacteriaceae. The two species resemble each other
in many ways; however, they differ in essential
details. Extensive data indicate that the overall
genome complexity in Salmonella is generally
10–20% greater than that in E. coli. In addition,
S. typhimurium is 1–4% higher in guanine-pluscytosine content than most E. coli strains (Ingraham
and Neidhardt, 1987). In the light of these
differences, the survival of the two species in open
environments has been shown to be different. Thus
Salmonella strains survived significantly longer in
terrestrial habitats in the majority of cases in
comparison to E. coli strains (Himathongkham
et al., 1999; Franz et al., 2005; Semenov et al.,
2007). Such differential survival might relate to
genome size or content or gene expression patterns
between the two species. We surmised that also the
within-E. coli genomic differences might correlate
with divergent survival rates. For instance, two
E. coli strains, C278 and C279 (different by enterobacterial repetitive intergenic consensus sequence
(ERIC)-PCR-based genomic fingerprinting), survived
differently in soil amended with swine manure
(Topp et al., 2003). Moreover, basal production of
toxin (Stx) by haemolytic uraemic syndrome-associated E. coli was higher than that by bovineassociated E. coli strains (Ritchie et al., 2003). In
addition, a reconsideration of the work of Kudva
et al. (1998) showed that at 23 1C a toxin-negative
strain of E. coli O157:H7 grew and survived better
than its toxin-positive counterpart, whereas no such
differences were found at lower temperatures. This
differential survival was found between days 15 and
55 of the experiment (Kudva et al., 1998), confirming an influence of genetic makeup (here, the
production of a toxin) on survival characteristics.
Shiga toxin-producing E. coli O157:H7, O11:H- and
O26:H11 survived for comparable periods of time
(up to 8 weeks) in bovine faeces, with rather similar
average decay rates at 25 1C (Fukushima et al., 1999),
although at 5 1C E. coli O157:H7 was superior in
survival after the first 4 weeks over the other two
strains. Similar results were shown for seawater,
where different specific mutations (rpoS, otsA, relA,
spoT, ompC and ompF) significantly influenced
E. coli survival (Rozen and Belkin, 2001). Hence,
particular characteristics encoded by the genome
present in some E. coli strains, but not in others
(like, for instance, the capacity to survive low
temperature under cow dung conditions), may have
been the cause of this differential survival, as the
production of toxins requires energy and therefore
imposes a fitness cost.
Fitness (growth rate) tests performed in rich
Tryptic Soy Broth (TSB), poor and rumen medium
under changing (aerobic versus anaerobic) conditions showed no difference in growth rates between
E. coli O157:H7 and commensalistic E. coli strains.
However, both types of strains had different carbon
substrate utilization patterns (Durso et al., 2004): of
95 carbon sources, 27 were oxidized by the
commensal E. coli but not by E. coli O157:H7 (Durso
et al., 2004). This difference did not affect their
growth in common media and also could not be
linked to any differential survival in the cow
stomach or dung. Finally, the variability across 57
commensal and pathogenic E. coli strains in utilization of carbon and energy sources as well as
catabolic and stress protection genes was low, but
such variation was clearly found across the different
E. coli strains (Ihssen et al., 2007). These results
suggest that functions affecting the microorganism’s
survival and growth, such as those of the central
metabolism that determine growth rates, are actually
quite broadly shared across the E. coli strains,
potentially yielding grossly comparable survival
rates in complex natural systems. On top of that,
particular E. coli strains may have acquired or
evolved specific systems—such as particular ironacquisition operons (Figure 3), and/or capacities to
withstand acidity and/or low temperature—that
allow them to be fitter in some secondary habitats.
However, these latter contentions need experimental validation.
Given the finding of a 2000-gene common E. coli
core genome (Figure 1), which might encompass all
genes that are of importance for environmental
hardiness and survival (but does not encompass
identifiable extraintestinal virulence-specific genes;
Touchon et al., 2009), we postulate that E. coli
genomes, next to providing overall cores that largely
determine metabolic flux on the one, and stress
tolerance on the other hand, incidentally (per strain
or group of strains) provide specific traits that
enhance their survival in open habitats.
On another matter, genes involved in virulence
are variably present across E. coli strains, and can
even be found on plasmids (To´th et al., 2009),
explaining their ready and rapid spread. However,
only 131 E. coli O157:H7-specific proteins out of
1632 were associated with virulence, indicating that
there is a limit to what genomes comprise. If E. coli
O157:H7 would be transmitted directly from human
to human, then the mere presence of the virulence
Survival of E. coli in the environment
JD van Elsas et al
The ISME Journal
genes—next to the core—might have been sufficient
for rapid pathogenesis, resulting in O157:H7 outcompeting commensal E. coli. However, outbreaks
of E. coli O157:H7 usually come from infested
primary food, suggesting that pathogenic and commensal E. coli differ in other traits that affect their
survival, allowing E. coli O157:H7 to be (overall)
successful (Durso et al., 2004).
Conclusions and prospects for further
It is known that the combination of abiotic (availability of energy and nutrient sources, pH, moisture
and temperature) as well as biotic (indigenous
microflora, including protozoa) factors sets the
conditions under which E. coli needs to survive.
Extreme or fluctuating values of each parameter
pose varying levels of stress to the cells, leading to
different survival times. Hence, these factors per se
will determine E. coli survivability in natural
systems by their direct effects on the exposed cells.
Given the complexity and heterogeneity of most
natural environments, it is intrinsically difficult to
predict the fate of E. coli populations facing the
combined environmental effects. Recent studies on
the effect of microbial diversity and community
structure on the persistence of introduced E. coli
O157:H7 in soil have nevertheless shown the
emergence of relationships between the microbial
diversity of the system, abiotic factors and the
pathogen’s invasibility (van Elsas et al., 2007;
Semenov et al., 2008).
In addition, the relationship between E. coli
genotype and its phenotype, in terms of its environmental persistence, is not at all clear. As outlined in
the foregoing, the genotypes within the species
share a core set of genes (Figure 1; Touchon et al.,
2009) that collectively broadly determines the
organism’s growth and metabolic characteristics as
well as its stress resistance in natural environments.
Traits that are additive to the ones encoded by the
core set of genes, for instance the extra capacity to
acquire iron in many strains (Figure 3) or the acid
resistance in E. coli O157:H7, can be present in
particular E. coli genotypes, but we lack extensive knowledge about their occurrence, functioning
and fitness-enhancing effects. Future research
should address the intriguing hypothesis that some
of the E. coli strains, next to their evolution to
fitness enhancement in their primary environment
(in association with their host), also have evolved
towards an enhanced fitness in open environments.
As a conclusion, we have to reexamine our knowledge about the survival of E. coli in open systems
with respect to the effect of the environmental
factors and the organism’s genotype. It has been
traditionally assumed that E. coli shows natural
declines in open environments. However, forming
an environmental reservoir of a given size in
different conditions, the bacterium can cause risks
to human health. The factors that determine the rate
of survival of particular E. coli strains, and thus the
risks, are not (yet) easily predictable, and our
capability to understand the effects of the secondary
habitat (especially soil and water resources) on
E. coli behaviour will be paramount to our abilities
to manage the organism from both environmental
and public health perspectives.
This study was funded by the NATO Programme
Security through Science ESP.EAP.CLG 981785. The Soil
Biotechnology Foundation also provided support to
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Online Academic Help With Different Subjects


Students barely have time to read. We got you! Have your literature essay or book review written without having the hassle of reading the book. You can get your literature paper custom-written for you by our literature specialists.


Do you struggle with finance? No need to torture yourself if finance is not your cup of tea. You can order your finance paper from our academic writing service and get 100% original work from competent finance experts.

Computer science

Computer science is a tough subject. Fortunately, our computer science experts are up to the match. No need to stress and have sleepless nights. Our academic writers will tackle all your computer science assignments and deliver them on time. Let us handle all your python, java, ruby, JavaScript, php , C+ assignments!


While psychology may be an interesting subject, you may lack sufficient time to handle your assignments. Don’t despair; by using our academic writing service, you can be assured of perfect grades. Moreover, your grades will be consistent.


Engineering is quite a demanding subject. Students face a lot of pressure and barely have enough time to do what they love to do. Our academic writing service got you covered! Our engineering specialists follow the paper instructions and ensure timely delivery of the paper.


In the nursing course, you may have difficulties with literature reviews, annotated bibliographies, critical essays, and other assignments. Our nursing assignment writers will offer you professional nursing paper help at low prices.


Truth be told, sociology papers can be quite exhausting. Our academic writing service relieves you of fatigue, pressure, and stress. You can relax and have peace of mind as our academic writers handle your sociology assignment.


We take pride in having some of the best business writers in the industry. Our business writers have a lot of experience in the field. They are reliable, and you can be assured of a high-grade paper. They are able to handle business papers of any subject, length, deadline, and difficulty!


We boast of having some of the most experienced statistics experts in the industry. Our statistics experts have diverse skills, expertise, and knowledge to handle any kind of assignment. They have access to all kinds of software to get your assignment done.


Writing a law essay may prove to be an insurmountable obstacle, especially when you need to know the peculiarities of the legislative framework. Take advantage of our top-notch law specialists and get superb grades and 100% satisfaction.

What discipline/subjects do you deal in?

We have highlighted some of the most popular subjects we handle above. Those are just a tip of the iceberg. We deal in all academic disciplines since our writers are as diverse. They have been drawn from across all disciplines, and orders are assigned to those writers believed to be the best in the field. In a nutshell, there is no task we cannot handle; all you need to do is place your order with us. As long as your instructions are clear, just trust we shall deliver irrespective of the discipline.

Are your writers competent enough to handle my paper?

Our essay writers are graduates with bachelor's, masters, Ph.D., and doctorate degrees in various subjects. The minimum requirement to be an essay writer with our essay writing service is to have a college degree. All our academic writers have a minimum of two years of academic writing. We have a stringent recruitment process to ensure that we get only the most competent essay writers in the industry. We also ensure that the writers are handsomely compensated for their value. The majority of our writers are native English speakers. As such, the fluency of language and grammar is impeccable.

What if I don’t like the paper?

There is a very low likelihood that you won’t like the paper.

Reasons being:

  • When assigning your order, we match the paper’s discipline with the writer’s field/specialization. Since all our writers are graduates, we match the paper’s subject with the field the writer studied. For instance, if it’s a nursing paper, only a nursing graduate and writer will handle it. Furthermore, all our writers have academic writing experience and top-notch research skills.
  • We have a quality assurance that reviews the paper before it gets to you. As such, we ensure that you get a paper that meets the required standard and will most definitely make the grade.

In the event that you don’t like your paper:

  • The writer will revise the paper up to your pleasing. You have unlimited revisions. You simply need to highlight what specifically you don’t like about the paper, and the writer will make the amendments. The paper will be revised until you are satisfied. Revisions are free of charge
  • We will have a different writer write the paper from scratch.
  • Last resort, if the above does not work, we will refund your money.

Will the professor find out I didn’t write the paper myself?

Not at all. All papers are written from scratch. There is no way your tutor or instructor will realize that you did not write the paper yourself. In fact, we recommend using our assignment help services for consistent results.

What if the paper is plagiarized?

We check all papers for plagiarism before we submit them. We use powerful plagiarism checking software such as SafeAssign, LopesWrite, and Turnitin. We also upload the plagiarism report so that you can review it. We understand that plagiarism is academic suicide. We would not take the risk of submitting plagiarized work and jeopardize your academic journey. Furthermore, we do not sell or use prewritten papers, and each paper is written from scratch.

When will I get my paper?

You determine when you get the paper by setting the deadline when placing the order. All papers are delivered within the deadline. We are well aware that we operate in a time-sensitive industry. As such, we have laid out strategies to ensure that the client receives the paper on time and they never miss the deadline. We understand that papers that are submitted late have some points deducted. We do not want you to miss any points due to late submission. We work on beating deadlines by huge margins in order to ensure that you have ample time to review the paper before you submit it.

Will anyone find out that I used your services?

We have a privacy and confidentiality policy that guides our work. We NEVER share any customer information with third parties. Noone will ever know that you used our assignment help services. It’s only between you and us. We are bound by our policies to protect the customer’s identity and information. All your information, such as your names, phone number, email, order information, and so on, are protected. We have robust security systems that ensure that your data is protected. Hacking our systems is close to impossible, and it has never happened.

How our Assignment  Help Service Works

1.      Place an order

You fill all the paper instructions in the order form. Make sure you include all the helpful materials so that our academic writers can deliver the perfect paper. It will also help to eliminate unnecessary revisions.

2.      Pay for the order

Proceed to pay for the paper so that it can be assigned to one of our expert academic writers. The paper subject is matched with the writer’s area of specialization.

3.      Track the progress

You communicate with the writer and know about the progress of the paper. The client can ask the writer for drafts of the paper. The client can upload extra material and include additional instructions from the lecturer. Receive a paper.

4.      Download the paper

The paper is sent to your email and uploaded to your personal account. You also get a plagiarism report attached to your paper.

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