Invasion Of Pathogenic Escherichia
Added on 2022-08-17
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Recent advances in adherence and invasion of pathogenic
Escherichia coli
Anjana Kalita1,*, Jia Hu1,*, and Alfredo G. Torres1,2,†
1Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston,
Texas, 77555, USA
2Department of Pathology, University of Texas Medical Branch, Galveston, Texas, 77555, USA
Abstract
Purpose of review—Colonization of the host epithelia by pathogenic Escherichia coli is
influenced by the ability of the bacteria to interact with host surfaces. Because the initial step of an
E. coli infection is to adhere, invade, and persist within host cells, some strategies used by
intestinal and extra-intestinal E. coli to infect host cell are presented.
Recent findings—This review highlights recent progress understanding how extra-intestinal
pathogenic E. coli strains express specific adhesins/invasins that allow colonization of the urinary
tract or the meninges, while intestinal E. coli strains are able to colonize different regions of the
intestinal tract using other specialized adhesins/invasins. Finally, evaluation of, different diets and
environmental conditions regulating the colonization of these pathogens is discussed.
Summary—Discovery of new interactions between pathogenic E. coli and the host epithelial
cells unravels the need of more mechanistic studies that can provide new clues in how to combat
these infections.
Keywords
enterohemorrhagic E. coli; enteropathogenic; enterotoxigenic; uropathogenic; enteroaggregative;
adherent invasive E. coli
Introduction
Escherichia coli are commonly found as part of the gut flora, where it is the predominant
aerobic organism, living in symbiosis with its vertebrate host. However, there are several
categories of E. coli strains that have acquired the ability to cause pathogenic processes in
the host (1). These E. coli strains can cause intestinal (enteritis, diarrhea, or dysentery), or.
extra-intestinal diseases (urinary tract infections, sepsis, or meningitis) (2, 3). To cause
infection, pathogenic E. coli interact with the mucosa, by either attaching to the epithelial
†Corresponding author: Alfredo G. Torres, PhD. UTMB, Department of Microbiology and Immunology, Galveston, Texas, 77555
Phone (409) 747 0189; Fax (409) 747 6869; altorres@utmb.edu.
*These authors contributed equally to this work
Conflicts of interest
There are no conflicts of interest.
NIH Public Access
Author Manuscript
Curr Opin Infect Dis. Author manuscript; available in PMC 2015 October 01.
Published in final edited form as:
Curr Opin Infect Dis. 2014 October ; 27(5): 459–464. doi:10.1097/QCO.0000000000000092.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Escherichia coli
Anjana Kalita1,*, Jia Hu1,*, and Alfredo G. Torres1,2,†
1Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston,
Texas, 77555, USA
2Department of Pathology, University of Texas Medical Branch, Galveston, Texas, 77555, USA
Abstract
Purpose of review—Colonization of the host epithelia by pathogenic Escherichia coli is
influenced by the ability of the bacteria to interact with host surfaces. Because the initial step of an
E. coli infection is to adhere, invade, and persist within host cells, some strategies used by
intestinal and extra-intestinal E. coli to infect host cell are presented.
Recent findings—This review highlights recent progress understanding how extra-intestinal
pathogenic E. coli strains express specific adhesins/invasins that allow colonization of the urinary
tract or the meninges, while intestinal E. coli strains are able to colonize different regions of the
intestinal tract using other specialized adhesins/invasins. Finally, evaluation of, different diets and
environmental conditions regulating the colonization of these pathogens is discussed.
Summary—Discovery of new interactions between pathogenic E. coli and the host epithelial
cells unravels the need of more mechanistic studies that can provide new clues in how to combat
these infections.
Keywords
enterohemorrhagic E. coli; enteropathogenic; enterotoxigenic; uropathogenic; enteroaggregative;
adherent invasive E. coli
Introduction
Escherichia coli are commonly found as part of the gut flora, where it is the predominant
aerobic organism, living in symbiosis with its vertebrate host. However, there are several
categories of E. coli strains that have acquired the ability to cause pathogenic processes in
the host (1). These E. coli strains can cause intestinal (enteritis, diarrhea, or dysentery), or.
extra-intestinal diseases (urinary tract infections, sepsis, or meningitis) (2, 3). To cause
infection, pathogenic E. coli interact with the mucosa, by either attaching to the epithelial
†Corresponding author: Alfredo G. Torres, PhD. UTMB, Department of Microbiology and Immunology, Galveston, Texas, 77555
Phone (409) 747 0189; Fax (409) 747 6869; altorres@utmb.edu.
*These authors contributed equally to this work
Conflicts of interest
There are no conflicts of interest.
NIH Public Access
Author Manuscript
Curr Opin Infect Dis. Author manuscript; available in PMC 2015 October 01.
Published in final edited form as:
Curr Opin Infect Dis. 2014 October ; 27(5): 459–464. doi:10.1097/QCO.0000000000000092.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
cells and in some instances, invading the target host cells. Because bacterial adhesion and/or
invasion to/into host cells are the first step during infection, it is necessary to understand at a
molecular level the mechanisms mediating these initial interactions. This article focus on
reviewing recent progress on the understanding of the adhesion/invasion mechanisms used
by intestinal and extra-intestinal pathogenic E. coli during colonization of the host cells.
Enterohemorrhagic E. coli (EHEC)
EHEC are a category of pathogenic E. coli that colonize the human large intestine and which
can cause bloody diarrhea, or a systemic process known as hemolytic uremic syndrome (4).
EHEC strains are characterized by the production of Shiga toxin and the formation of
attaching and effacing intestinal lesions (Figure 1). Cattle are a main reservoir for EHEC
strains; however several vegetables and fruits can serve as vehicles for EHEC outbreaks (5).
EHEC colonization is impacted by nutrient availability and dietary choice. Zumbrun et al
found that dietary fiber content affects susceptibility to E. coli O157:H7 infection in mice
(6). They treated BALB/c mice with high fiber diet (10% guar gum) or low fiber diet (2%
guar gum) for two weeks and then mice were challenge with 109 to 1011 cfu of E. coli
O157:H7. The results showed that mice fed with high fiber diet had enhanced levels of
butyrate that temporally increased the expression of the Shiga toxin receptor Gb3.
Therefore, mice exhibited greater E. coli O157:H7 colonization and reduction in resident
Escherichia spp. Sheng et al also showed that cattle fed a hay diet are colonized by EHEC
for a longer period of time than grain fed cattle (7). Different diets regulate the colonization
of E. coli O157:H7 by altering the composition of gastrointestinal tract microbiota and the
study demonstrated that the bacterial SdiA sensor activates genes conferring EHEC acid
resistance, increasing efficient colonization of the cattle mucosa (8).
Modulation of host signals in the intestinal epithelia also affects EHEC colonization.
Intestinal epithelial cells produced SIGIRR, a negative regulator of interleukin (IL)-1 and
TLR signaling, that makes the cells hypo-responsive (9, 10). To address whether hypo-
responsiveness affects enteric host defense, Sham et al challenge Sigirr deficient (−/−) mice
with the murine pathogen, EHEC-related, Citrobacter rodentium and showed that Sigirr−/−
mice are more susceptible to bacterial infection and had a dramatic loss of microbiota (11).
The study showed that this host signaling mechanism promotes commensal dependent
resistance to EHEC colonization.
Type III secretion system (TTSS) is required for EHEC colonization and attaching and
effacing lesion formation. This syringe-like structure used to inject virulence factors into the
host cell is exquisitely regulated. Hansen et al revealed that tyrosine phosphorylation in
EHEC mediates signaling of virulence properties, including the type III secretion system
(12). SspA is a known regulator of the TTSS (13) and a phosphorylated tyrosine residue of
this protein positively affects expression and secretion of type III secretion system proteins.
Branchu et al also found a new regulator of the TTSS (14) known as the NO-sensor
regulator, NsrR. Nitric oxide (NO) reduced EHEC adherence to intestinal epithelial cells, by
causing the detachment of the NsrR activator from the type III secretion system-encoding
operons (LEE1/4/5), limiting colonization.
Kalita et al. Page 2
Curr Opin Infect Dis. Author manuscript; available in PMC 2015 October 01.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
invasion to/into host cells are the first step during infection, it is necessary to understand at a
molecular level the mechanisms mediating these initial interactions. This article focus on
reviewing recent progress on the understanding of the adhesion/invasion mechanisms used
by intestinal and extra-intestinal pathogenic E. coli during colonization of the host cells.
Enterohemorrhagic E. coli (EHEC)
EHEC are a category of pathogenic E. coli that colonize the human large intestine and which
can cause bloody diarrhea, or a systemic process known as hemolytic uremic syndrome (4).
EHEC strains are characterized by the production of Shiga toxin and the formation of
attaching and effacing intestinal lesions (Figure 1). Cattle are a main reservoir for EHEC
strains; however several vegetables and fruits can serve as vehicles for EHEC outbreaks (5).
EHEC colonization is impacted by nutrient availability and dietary choice. Zumbrun et al
found that dietary fiber content affects susceptibility to E. coli O157:H7 infection in mice
(6). They treated BALB/c mice with high fiber diet (10% guar gum) or low fiber diet (2%
guar gum) for two weeks and then mice were challenge with 109 to 1011 cfu of E. coli
O157:H7. The results showed that mice fed with high fiber diet had enhanced levels of
butyrate that temporally increased the expression of the Shiga toxin receptor Gb3.
Therefore, mice exhibited greater E. coli O157:H7 colonization and reduction in resident
Escherichia spp. Sheng et al also showed that cattle fed a hay diet are colonized by EHEC
for a longer period of time than grain fed cattle (7). Different diets regulate the colonization
of E. coli O157:H7 by altering the composition of gastrointestinal tract microbiota and the
study demonstrated that the bacterial SdiA sensor activates genes conferring EHEC acid
resistance, increasing efficient colonization of the cattle mucosa (8).
Modulation of host signals in the intestinal epithelia also affects EHEC colonization.
Intestinal epithelial cells produced SIGIRR, a negative regulator of interleukin (IL)-1 and
TLR signaling, that makes the cells hypo-responsive (9, 10). To address whether hypo-
responsiveness affects enteric host defense, Sham et al challenge Sigirr deficient (−/−) mice
with the murine pathogen, EHEC-related, Citrobacter rodentium and showed that Sigirr−/−
mice are more susceptible to bacterial infection and had a dramatic loss of microbiota (11).
The study showed that this host signaling mechanism promotes commensal dependent
resistance to EHEC colonization.
Type III secretion system (TTSS) is required for EHEC colonization and attaching and
effacing lesion formation. This syringe-like structure used to inject virulence factors into the
host cell is exquisitely regulated. Hansen et al revealed that tyrosine phosphorylation in
EHEC mediates signaling of virulence properties, including the type III secretion system
(12). SspA is a known regulator of the TTSS (13) and a phosphorylated tyrosine residue of
this protein positively affects expression and secretion of type III secretion system proteins.
Branchu et al also found a new regulator of the TTSS (14) known as the NO-sensor
regulator, NsrR. Nitric oxide (NO) reduced EHEC adherence to intestinal epithelial cells, by
causing the detachment of the NsrR activator from the type III secretion system-encoding
operons (LEE1/4/5), limiting colonization.
Kalita et al. Page 2
Curr Opin Infect Dis. Author manuscript; available in PMC 2015 October 01.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Enteropathogenic E. coli (EPEC)
EPEC isolates colonize the small intestine and are one of the leading causes of infantile fatal
diarrhea (15). In industrialized countries, there are sporadic diarrheal cases in daycare
facilities (16, 17). As for EHEC, EPEC uses the type III secretion system to form attaching
and effacing lesions (Figure 1). EPEC strains are subdivided into typical (tEPEC) and
atypical EPEC (aEPEC) based on the presence of EPEC adherence factor plasmid associated
with the tEPEC localized adherence pattern (18). Some aEPEC form diffuse (DA) or
aggregative adherence pattern and Hernandes et al (19) found that the DA pattern is
associated with the TTSS system and its suggested that the traslocon serves as the DA
adhesin.
Regarding the type III secretion system, recent studies have evaluated the role of the effector
protein NleB in pathogenesis. Deletion of nleB1 in C. rodentium caused significant
reduction in murine intestinal colonization (20), and NleB has also been shown to modulate
the host innate immune system by suppressing tumor necrosis factor (TNF)-mediated NF-
κB activation (21). Three studies have investigated the role of NleB1 in EPEC. Gao et al
focused on how NleB interfere with NF-κB (22). A proteomic screen was used to identify
the host GAPDH as NleB-interacting protein, which results in modification of GAPDH and
inhibition of NF-κB-dependent innate immune responses. The other two groups discovered
that NleB blocks host death receptor signaling (23, 24), by interacting with two death
receptor-signaling proteins, TRADD and FADD. NleB is the first known bacterial virulence
factor to target death receptor signaling and it has been suggested that blocking this
signaling mechanism may facilitate EPEC and EHEC colonization.
Other studies evaluated ways to reduce EPEC adhesion to host cells. Pan et al expressed
synthetic tetrameric-branched peptide that enhanced the expression of Mucin 3 (25). They
found that Mucin 3 interacted with EPEC and EHEC and reduced their binding to epithelial
cells. In other study, Salcedo et al showed that the combination of gangliosides and sialic
acid were able to interfere with EPEC and EHEC adhesion to Caco-2 cells (26).
Enterotoxigenic E. coli (ETEC)
ETEC colonizes the human small intestine and is responsible for neonatal diarrhea in
developing countries as well as “travelers’ diarrhea” (27). ETEC adherence to the intestinal
mucosa is mainly mediated by diverse adhesive structures known as colonization factors,
which in combination with the heat-labile (LT) and/or heat-stable (ST) enterotoxins, causes
disruption of fluid homeostasis in the host, resulting in diarrhea (2, 28) (Figure 1).
Guevara et al recently investigated one colonization factors, the CS21 pilus, and its role in
adherence and pathogenesis in vivo (29). They found that ETEC CS21 (Longus) adherence
to primary intestinal cells was inhibited by anti-LngA sera and the purified LngA protein. In
vivo intra-stomach administration of CS21-expressing ETEC strain contributes to 100%
lethality of newborn mice, which was reduced in the lngA mutant. A separate study
investigated the role of the LT toxin in ETEC colonization (30). The authors observed
enhanced adherence to IPEC-J2 cells by various isogenic ETEC constructs carrying different
forms of the LT toxin (K88/LT wild type, attenuated toxin form [K88/LTR192G] and
Kalita et al. Page 3
Curr Opin Infect Dis. Author manuscript; available in PMC 2015 October 01.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
EPEC isolates colonize the small intestine and are one of the leading causes of infantile fatal
diarrhea (15). In industrialized countries, there are sporadic diarrheal cases in daycare
facilities (16, 17). As for EHEC, EPEC uses the type III secretion system to form attaching
and effacing lesions (Figure 1). EPEC strains are subdivided into typical (tEPEC) and
atypical EPEC (aEPEC) based on the presence of EPEC adherence factor plasmid associated
with the tEPEC localized adherence pattern (18). Some aEPEC form diffuse (DA) or
aggregative adherence pattern and Hernandes et al (19) found that the DA pattern is
associated with the TTSS system and its suggested that the traslocon serves as the DA
adhesin.
Regarding the type III secretion system, recent studies have evaluated the role of the effector
protein NleB in pathogenesis. Deletion of nleB1 in C. rodentium caused significant
reduction in murine intestinal colonization (20), and NleB has also been shown to modulate
the host innate immune system by suppressing tumor necrosis factor (TNF)-mediated NF-
κB activation (21). Three studies have investigated the role of NleB1 in EPEC. Gao et al
focused on how NleB interfere with NF-κB (22). A proteomic screen was used to identify
the host GAPDH as NleB-interacting protein, which results in modification of GAPDH and
inhibition of NF-κB-dependent innate immune responses. The other two groups discovered
that NleB blocks host death receptor signaling (23, 24), by interacting with two death
receptor-signaling proteins, TRADD and FADD. NleB is the first known bacterial virulence
factor to target death receptor signaling and it has been suggested that blocking this
signaling mechanism may facilitate EPEC and EHEC colonization.
Other studies evaluated ways to reduce EPEC adhesion to host cells. Pan et al expressed
synthetic tetrameric-branched peptide that enhanced the expression of Mucin 3 (25). They
found that Mucin 3 interacted with EPEC and EHEC and reduced their binding to epithelial
cells. In other study, Salcedo et al showed that the combination of gangliosides and sialic
acid were able to interfere with EPEC and EHEC adhesion to Caco-2 cells (26).
Enterotoxigenic E. coli (ETEC)
ETEC colonizes the human small intestine and is responsible for neonatal diarrhea in
developing countries as well as “travelers’ diarrhea” (27). ETEC adherence to the intestinal
mucosa is mainly mediated by diverse adhesive structures known as colonization factors,
which in combination with the heat-labile (LT) and/or heat-stable (ST) enterotoxins, causes
disruption of fluid homeostasis in the host, resulting in diarrhea (2, 28) (Figure 1).
Guevara et al recently investigated one colonization factors, the CS21 pilus, and its role in
adherence and pathogenesis in vivo (29). They found that ETEC CS21 (Longus) adherence
to primary intestinal cells was inhibited by anti-LngA sera and the purified LngA protein. In
vivo intra-stomach administration of CS21-expressing ETEC strain contributes to 100%
lethality of newborn mice, which was reduced in the lngA mutant. A separate study
investigated the role of the LT toxin in ETEC colonization (30). The authors observed
enhanced adherence to IPEC-J2 cells by various isogenic ETEC constructs carrying different
forms of the LT toxin (K88/LT wild type, attenuated toxin form [K88/LTR192G] and
Kalita et al. Page 3
Curr Opin Infect Dis. Author manuscript; available in PMC 2015 October 01.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
expressing just the B subunit [K88/LTB]), in contrast to the attenuated phenotype of the LT-
negative construct. LT+ strains blocking binding of wild type ETEC strain to IPEC-J2 cells
suggested that LT-driven adherence alters net surface charge on epithelial cells. Another
study evaluated the transcriptional pattern of 214 genes at different time points following
interaction of prototype ETEC E24377A with epithelial cells (31). The study found a
prominent alteration of genes associated with motility, adhesion, toxin production, and
global regulatory mechanisms, such as those linked to cAMP receptor protein and c-di-
GMP, upon ETEC-host interaction, which suggested that ETEC coordinated its responses to
the host environment by sequential activation of different virulence factors.
Among those ETEC strains infecting animals, the most common adhesive fimbriae include
K88 or K99 (also called F4 and F5) (28). Recently, Zhou et al have demonstrated that
deletion of fliC (encoding the major flagellin protein) and/or the faeG (encoding the F4
major fimbrial subunit) from ETEC strain C83902 significantly reduced its ability to adhere
to porcine epithelia IPEC-J2 cells, but also impacting biofilm formation and quorum sensing
(32). Interestingly, another study found an alternative way to block the adherence of ETEC
K88 to IPEC-J2 by using ETEC anti-adhesives, including casein glycomacropeptide,
exopolysaccharide, and vegetable extract (locust bean or wheat bran) (33). Finally, studies
with human milk and commercial infant formulas found that the main gangliosides (GM3,
GD3, GM1) and free sialic acid (Neu5Ac) are able to impede the adhesion of several
pathogenic bacteria, including ETEC (26). Other dietary supplements, such as plantain NSP,
also hampered the adherence of ETEC to Caco-2 cells, and has been suggested that blocking
M-cell bacterial translocation can subsequently prevent diarrheal episodes (34).
Enteroaggregative E. coli (EAEC)
EAEC are a major cause of acute and persistent diarrhea in the small intestine of children
and adults worldwide, including industrialized countries (35). EAEC is also responsible for
sporadic cases and several outbreaks (36). At an initial stage of infection, EAEC adhere in a
characteristic “stacked-brick” formation to host intestinal mucosa; forming a thick mucoid
biofilm. The adherence process is mainly mediated by fimbrial structures called aggregative
adherence fimbriae (AAF) (35) (Figure 1). Additionally, several EAEC virulence-related
genes have been described but their role in the clinical outcome of infection is not
completely defined.
A study recently confirmed a high prevalence, endemicity and heterogeneity of EAEC
strains, and found that the plasmid-encoded toxin or AAF/II fimbrial subunit genes were
associated significantly with disease (37). However, this study also demonstrated that the
pathophysiology of EAEC infections involves a complex and dynamic modulation of several
virulence factors. Another study identified an association of the EAEC virulence-encoded
aggR gene (virulence regulator), pCDV432 plasmid, and additional virulence gene products,
including dispersin and the Air adhesin in 90% of the diarrheagenic isolates that
distinguished them from non-diarrheagenic EAEC strains, suggesting heterogeneity among
highly pathogenic EAEC strains (38).
Kalita et al. Page 4
Curr Opin Infect Dis. Author manuscript; available in PMC 2015 October 01.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
negative construct. LT+ strains blocking binding of wild type ETEC strain to IPEC-J2 cells
suggested that LT-driven adherence alters net surface charge on epithelial cells. Another
study evaluated the transcriptional pattern of 214 genes at different time points following
interaction of prototype ETEC E24377A with epithelial cells (31). The study found a
prominent alteration of genes associated with motility, adhesion, toxin production, and
global regulatory mechanisms, such as those linked to cAMP receptor protein and c-di-
GMP, upon ETEC-host interaction, which suggested that ETEC coordinated its responses to
the host environment by sequential activation of different virulence factors.
Among those ETEC strains infecting animals, the most common adhesive fimbriae include
K88 or K99 (also called F4 and F5) (28). Recently, Zhou et al have demonstrated that
deletion of fliC (encoding the major flagellin protein) and/or the faeG (encoding the F4
major fimbrial subunit) from ETEC strain C83902 significantly reduced its ability to adhere
to porcine epithelia IPEC-J2 cells, but also impacting biofilm formation and quorum sensing
(32). Interestingly, another study found an alternative way to block the adherence of ETEC
K88 to IPEC-J2 by using ETEC anti-adhesives, including casein glycomacropeptide,
exopolysaccharide, and vegetable extract (locust bean or wheat bran) (33). Finally, studies
with human milk and commercial infant formulas found that the main gangliosides (GM3,
GD3, GM1) and free sialic acid (Neu5Ac) are able to impede the adhesion of several
pathogenic bacteria, including ETEC (26). Other dietary supplements, such as plantain NSP,
also hampered the adherence of ETEC to Caco-2 cells, and has been suggested that blocking
M-cell bacterial translocation can subsequently prevent diarrheal episodes (34).
Enteroaggregative E. coli (EAEC)
EAEC are a major cause of acute and persistent diarrhea in the small intestine of children
and adults worldwide, including industrialized countries (35). EAEC is also responsible for
sporadic cases and several outbreaks (36). At an initial stage of infection, EAEC adhere in a
characteristic “stacked-brick” formation to host intestinal mucosa; forming a thick mucoid
biofilm. The adherence process is mainly mediated by fimbrial structures called aggregative
adherence fimbriae (AAF) (35) (Figure 1). Additionally, several EAEC virulence-related
genes have been described but their role in the clinical outcome of infection is not
completely defined.
A study recently confirmed a high prevalence, endemicity and heterogeneity of EAEC
strains, and found that the plasmid-encoded toxin or AAF/II fimbrial subunit genes were
associated significantly with disease (37). However, this study also demonstrated that the
pathophysiology of EAEC infections involves a complex and dynamic modulation of several
virulence factors. Another study identified an association of the EAEC virulence-encoded
aggR gene (virulence regulator), pCDV432 plasmid, and additional virulence gene products,
including dispersin and the Air adhesin in 90% of the diarrheagenic isolates that
distinguished them from non-diarrheagenic EAEC strains, suggesting heterogeneity among
highly pathogenic EAEC strains (38).
Kalita et al. Page 4
Curr Opin Infect Dis. Author manuscript; available in PMC 2015 October 01.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
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