Human antibody response to longus type IV pilus and study of its prevalence among enterotoxigenic Escherichia coli in Bangladesh by using monoclonal antibodies

Colonization factors of human and animal-specific enterotoxigenic Escherichia coli (ETEC)

Colonization factors (CFs) are major virulence factors of enterotoxigenic Escherichia coli (ETEC). This pathogen is among the most common causes of bacterial diarrhea in children in low- and middle-income countries, travelers, and livestock. CFs are major candidate antigens in vaccines under development as preventive measures against ETEC infections in humans and livestock. Recent molecular studies have indicated that newly identified CFs on human ETEC are closely related to animal ETEC CFs. Increased knowledge of pathogenic mechanisms, immunogenicity, regulation, and expression of ETEC CFs, as well as the possible spread of animal ETEC to humans, may facilitate the future development of ETEC vaccines for humans and animals. Here, we present an updated review of CFs in ETEC.

Recombinant Escherichia coli BL21 with LngA Variants from ETEC E9034A Promotes Adherence to HT-29 Cells

The CS21 pilus produced by enterotoxigenic Escherichia coli (ETEC) is involved in adherence to HT-29 intestinal cells. The CS21 pilus assembles proteins encoded by 14 genes clustered into the lng operon.

AIM

This study aimed to determine whether E. coli BL21 (ECBL) transformed with the lng operon lacking the lngA gene (pE9034AΔlngA) and complemented in trans with lngA variants of ETEC clinical strains, as well as point substitutions, exhibited modified adherence to HT-29 cells.

METHODS

A kanamycin cassette was used to replace the lngA gene in the lng operon of the E9034A strain, and the construct was transformed into the ECBL strain. The pJET1.2 vector carrying lngA genes with allelic variants was transformed into ECBLpE9034AΔlngA (ECBLΔlngA). The point substitutions were performed in the pJETlngA_FMU073332 vector.

RESULTS

Bioinformatic alignment analysis of the LngA proteins showed hypervariable regions and clustered the clinical ETEC strains into three groups. Variations in amino acid residues affect the adherence percentages of recombinant ECBL strains with lngA variants and site-specific mutations with HT-29 cells.

CONCLUSION

In this study, ECBL carrying the lng operon harboring lngA variants of six clinical ETEC strains, as well as point substitutions, exerted an effect on the adherence of ECBL to HT-29 cells, thereby confirming the importance of the CS21 pilus in adherence.

Feasibility of avian antibodies as prophylaxis against enterotoxigenic escherichia coli colonization

Background

This research aims to evaluate the feasibility of using avian immunoglobulins (IgY) raised against adhesion factors of enterotoxigenic Escherichia coli (ETEC) as prophylaxis of diarrheal illness caused by these pathogens. ETEC requires adhesion to human intestinal epithelial cells as a primary step in establishing enteric infection. Therefore, inhibition of adhesion may prevent such infections and reduce clinical burdens of diarrheal illness.

Methods

IgY samples were prepared from eggs of hens immunized with an adhesin-tip multiepitope fusion antigen (MEFA), developed against nine adhesin tip epitopes derived from clinically relevant ETEC strains. The resulting IgY was evaluated for its ability to inhibit adhesion of ETEC to cell-surface targets. Potential impacts of anti-MEFA IgY on growth of both pathogenic and commensal E. coli isolates were also evaluated.

Results

Enzyme linked immunosorbent assay (ELISA) titers were achieved for IgY targeting each of the nine individual epitopes included in the adhesin-tip MEFA. Furthermore, anti-MEFA titers exceeding 1:2¹⁹ were sustained for at least 23 weeks. All ETEC strains used in design of the adhesin-tip MEFA, and five of five clinical ETEC strains were significantly (P < 0.05) inhibited from adhesion to mammalian cells in culture.

Conclusions

These findings demonstrate that IgY targeting ETEC adhesin-tip MEFA have the potential to disrupt in vitro adherence of ETEC. A formulation containing adhesin-tip MEFA IgY can be considered a potential candidate for in vivo evaluation as prophylaxis of diarrheal diseases. Animal studies of this formulation are planned.

The role of CFA/I in adherence and toxin delivery by ETEC expressing multiple colonization factors in the human enteroid model

Enterotoxigenic Escherichia coli (ETEC) is a primary causative agent of diarrhea in travelers and young children in low-to-middle-income countries (LMICs). ETEC adhere to intestinal epithelia via colonization factors (CFs) and secrete heat-stable toxin (ST) and/or heat-labile toxin (LT), causing dysregulated cellular ion transport and water secretion. ETEC isolates often harbor genes encoding more than one CF that are targets as vaccine antigens. CFA/I is a major CF that is associated with ETEC that causes moderate-to-severe diarrhea and plays an important role in pathogenesis. The Global Enteric Multicenter Study finding that 78% of CFA/I-expressing ETEC also encode the minor CF CS21 prompted investigation of the combined role of these two CFs. Western blots and electron microscopy demonstrated growth media-dependent and strain-dependent differences in CFA/I and CS21 expression. The critical role of CFA/I in adherence by ETEC strains expressing CFA/I and CS21 was demonstrated using the human enteroid model and a series of CFA/I- and CS21-specific mutants. Furthermore, only anti-CFA/I antibodies inhibited adherence by global ETEC isolates expressing CFA/I and CS21. Delivery of ST and resulting cGMP secretion was measured in supernatants from infected enteroid monolayers, and strain-specific ST delivery and time-dependent cGMP production was observed. Interestingly, cGMP levels were similar across wildtype and CF-deficient strains, reflecting a limitation of this static aerobic infection model. Despite adherence by ETEC and delivery of ST, the enteroid monolayer integrity was not disrupted, as shown by the lack of decrease in transepithelial electrical resistance and the lack of IL-8 cytokines produced during infection. Taken together, these data demonstrate that targeting CFA/I in global clinical CFA/I-CS21 strains is sufficient for adherence inhibition, supporting a vaccine strategy that focuses on blocking major CFs. In addition, the human enteroid model has significant utility for the study of ETEC pathogenesis and evaluation of vaccine-induced functional antibody responses.

Phenotypic and genomic analyses of bacteriophages targeting environmental and clinical CS3-expressing enterotoxigenic Escherichia coli (ETEC) strains

Diarrhea due to infection of enterotoxigenic Escherichia coli (ETEC) is of great concern in several low and middle-income countries. ETEC infection is considered to be the most common cause of diarrhea in Bangladesh and is mainly spread through contaminated water and food. ETEC pathogenesis is mediated by the expression of enterotoxins and colonization factors (CFs) that target the intestinal mucosa. ETEC can survive for extended time periods in water, where they are likely to be attacked by bacteriophages. Antibiotic resistance is common amongst enteric pathogens and therefore is the use of bacteriophages (phage) as a therapeutic tool an interesting approach. This study was designed to identify novel phages that specifically target ETEC virulence factors. In total, 48 phages and 195 ETEC isolates were collected from water sources and stool samples. Amongst the identified ETEC specific phages, an enterobacteria phage T7, designated as IMM-002, showed a significant specificity towards colonization factor CS3-expressing ETEC isolates. Antibody-blocking and phage-neutralization assays revealed that CS3 is used as a host receptor for the IMM-002 phage. The bacterial CRISPR-Cas (Clustered Regularly Interspaced Short Palindromic Repeats-CRISPR-associated) defence mechanism can invoke immunity against phages. Genomic analyses coupled with plaque assay experiments indicate that the ETEC CRISPR-Cas system is involved in the resistance against the CS3-specific phage (IMM-002) and the previously identified CS7-specific phage (IMM-001). As environmental water serves as a reservoir for ETEC, it is important to search for new antimicrobial agents such as phages in environmental water as well as the human gut. A better understanding of how the interplay between ETEC-specific phages and ETEC isolates affects the ETEC diversity, both in environmental ecosystems and within the host, is important for the development of new treatments for ETEC infections.

Resistance Pattern and Molecular Characterization of Enterotoxigenic Escherichia coli (ETEC) Strains Isolated in Bangladesh

Background

Enterotoxigenic Escherichia coli (ETEC) is a common cause of bacterial infection leading to acute watery diarrhea in infants and young children as well as in travellers to ETEC endemic countries. Ciprofloxacin is a broad-spectrum antimicrobial agent nowadays used for the treatment of diarrhea. This study aimed to characterize ciprofloxacin resistant ETEC strains isolated from diarrheal patients in Bangladesh.

Methods

A total of 8580 stool specimens from diarrheal patients attending the icddr,b Dhaka hospital was screened for ETEC between 2005 and 2009. PCR and Ganglioside GM1- Enzyme Linked Immuno sorbent Assay (ELISA) was used for detection of Heat labile (LT) and Heat stable (ST) toxins of ETEC. Antimicrobial susceptibilities for commonly used antibiotics and the minimum inhibitory concentration (MIC) of nalidixic acid, ciprofloxacin and azithromycin were examined. DNA sequencing of representative ciprofloxacin resistant strains was performed to analyze mutations of the quinolone resistance-determining region of gyrA, gyrB, parC and parE. PCR was used for the detection of qnr, a plasmid mediated ciprofloxacin resistance gene. Clonal variations among ciprofloxacin resistant (Cip^R) and ciprofloxacin susceptible (Cip^S) strains were determined by Pulsed-field gel electrophoresis (PFGE).

Results

Among 1067 (12%) ETEC isolates identified, 42% produced LT/ST, 28% ST and 30% LT alone. Forty nine percent (n = 523) of the ETEC strains expressed one or more of the 13 tested colonization factors (CFs) as determined by dot blot immunoassay. Antibiotic resistance of the ETEC strains was observed as follows: ampicillin 66%, azithromycin 27%, ciprofloxacin 27%, ceftriazone 13%, cotrimaxazole 46%, doxycycline 44%, erythromycin 96%, nalidixic acid 83%, norfloxacin 27%, streptomycin 48% and tetracycline 42%. Resistance to ciprofloxacin increased from 13% in 2005 to 34% in 2009. None of the strains was resistant to mecillinam. The MIC of the nalidixic acid and ciprofloxacin of representative Cip^R strains were 256 μg/ml and 32μg/ml respectively. A single mutation (Ser⁸³-Leu) in gyrA was observed in the nalidixic acid resistant ETEC strains. In contrast, double mutation in gyrA (Ser⁸³-Leu, Asp⁸⁷-Asn) and a single mutation in parC (Glu⁸⁴-Ly) were found in ciprofloxacin resistant strains. Mutation of gyrB was not found in either the nalidixic acid or ciprofloxacin resistant strains. None of the ciprofloxacin resistant strains was found to be positive for the qnr gene. Diverse clones were identified from all ciprofloxacin resistant strains by PFGE analysis in both CF positive and CF negative ETEC strains.

Conclusion

Emergence of ciprofloxacin resistant ETEC strains results in a major challenge in current treatment strategies of ETEC diarrhea.

Shift in phenotypic characteristics of enterotoxigenic Escherichia coli (ETEC) isolated from diarrheal patients in Bangladesh

Background

Enterotoxigenic Escherichia coli (ETEC) is one of the most common causes of bacterial diarrhea. Over the last decade, from 1996 to 2012, changes in the virulence antigen properties of ETEC such as heat labile (LT) and heat stable (ST) toxins, colonization factors (CFs), and ‘O’-serogroups have been observed. The aim of this prospective study was to compare changes in antigenic profiles of ETEC strains isolated from a 2% surveillance system at the icddr,b hospital in Dhaka, Bangladesh between 2007–2012 and an earlier time period of 1996–1998 conducted at the same surveillance site.

Methodology

In the surveillance system every 50^th patient attending the hospital was screened for major enteric pathogens including ETEC, Vibrio cholerae, Shigella spp. and Salmonella spp. from January 2007 to December 2012.

Principal Findings

Of the 15,152 diarrheal specimens tested between 2007–2012, the overall rate of ETEC isolation was 11%; of these, 43% were LT/ST, 27% LT and 30% ST positive. Isolation rate of ST-ETEC (p<0.009) and LT/ST ETEC (p<0.011) during 2007–2012 period differed significantly compared to those seen between 1996–1998. In comparison to the 1996–1998 period, difference in CF profile of ETEC isolates during 2007–2012 was observed particularly for strains expressing CS7 (12.4%), CS14 (9.5%) and CS17 (10.0%). The predominant CF types were CS5+CS6, CFA/I, CS7, CS17, CS1+CS3, CS6 and CS14. The most common serogroups among the CF positive ETEC isolates were O115, O114, O6, O25 and O8. A strong association was found between CFs and ‘O’ serogroups i.e. between CS5+CS6 and (O115 and O126); CS7 and (O114), CFA/I and (O78 and O126), CS17 and (O8 and O167) and CS1/CS2+CS3 and (O6).

Conclusion

The analyses show a shift in prevalence of antigenic types of ETEC over the study period; the information is important in designing effective ETEC vaccines with broad protective coverage.

Diarrheal diseases constitute a major health problem in Bangladesh, where Vibrio cholerae and enterotoxigenic Escherichia coli (ETEC) are two most important causes of bacterial diarrhea. Prevention through vaccination is helpful to reduce the incidence and severity of diarrheal disease due to ETEC, particularly among children in low-resource settings. In this context, we collected stool and/or rectal swab (RS) specimens from patients with diarrhea between 2007 to 2012 under the 2% systematic routine surveillance system at the icddr,b hospital in Dhaka, Bangladesh and screened for ETEC infection. We tested the specimens for two major virulence factors of ETEC: toxins and colonization factors. In this research article, we have focused on changes in toxin as well as colonization factor profiles of ETEC strains isolated from diarrheal patients seeking care at the icddr,b hospital between 2007–2012 and an earlier time period of 1996–1998. We concluded that, such shift in antigenic profile of ETEC over the study period is important in designing effective ETEC vaccines with broad protective coverage.

Genome Sequence of Enterotoxigenic Escherichia coli Strain B2C

Enterotoxigenic Escherichia coli (ETEC) is a major cause of diarrheal disease around the globe, causing an estimated 380,000 deaths annually. The disease is caused by a wide variety of strains. Here, we report the genome sequence of ETEC strain B2C, which was isolated from an American soldier in Vietnam.

Enterotoxigenic Escherichia coli CS21 pilus contributes to adhesion to intestinal cells and to pathogenesis under in vivo conditions

Colonization surface antigens (CSs) represent key virulence-associated factors of enterotoxigenic Escherichia coli (ETEC) strains. They are required for gut colonization, the first step of the diarrhoeal disease process induced by these bacteria. One of the most prevalent CSs is CS21, or longus, a type IV pili associated with bacterial self-aggregation, protection against environmental stresses, biofilm formation and adherence to epithelial cell lines. The objectives of this study were to assess the role of CS21 in adherence to primary intestinal epithelial cells and to determine if CS21 contributes to the pathogenesis of ETEC infection in vivo. We evaluated adherence of a CS21-expressing wild-type ETEC strain and an isogenic CS21-mutant strain to pig-derived intestinal cell lines. To determine the role of CS21 in pathogenesis we used the above ETEC strains in a neonatal mice challenge infection model to assess mortality. Quantitative adherence assays confirmed that ETEC adheres to primary intestinal epithelial cells lines in a CS21-dependent manner. In addition, the CS21-mediated ETEC adherence to cells was specific as purified LngA protein, the CS21 major subunit, competed for binding with the CS21-expressing ETEC while specific anti-LngA antibodies blocked adhesion to intestinal cells. Neonatal DBA/2 mice died after intra-stomach administration of CS21-expressing strains while lack of CS21 expression drastically reduced the virulence of the wild-type ETEC strain in this animal model. Collectively these results further support the role of CS21 during ETEC infection and add new evidence on its in vivo relevance in pathogenesis.

Molecular characterization of enterotoxigenic Escherichia coli isolates recovered from children with diarrhea during a 4-year period (2007 to 2010) in Bolivia

Enterotoxigenic Escherichia coli (ETEC) is an important cause of childhood diarrhea. This study aimed to characterize ETEC strains isolated from Bolivian children aged <5 years according to enterotoxin profile, colonization factors (CFs), suggested virulence genes, and severity of disease. A total of 299 ETEC isolates recovered from children with diarrhea and 55 ETEC isolates from children without diarrhea (controls) were isolated over a period of 4 years. Strains expressing heat-labile toxin (LT) or heat-stable toxin (ST) alone were about equally common and twice as common as ETEC producing both toxins (20%). ETEC strains expressing human ST (STh) were more common in children aged <2 years, while ETEC strains expressing LT plus STh (LT/STh) were more frequent in 2- to 5-year-old children. Severity of disease was not related to the toxin profile of the strains. CF-positive isolates were more frequently identified in diarrheal samples than in control samples (P = 0.02). The most common CFs were CFA/I and CS14. CFA/I ETEC strains were more frequent in children aged <2 years than CS1+CS3 isolates and CS14 isolates, which were more prevalent in 2- to 5-year-old children. The presence of suggested ETEC virulence genes (clyA, eatA, tia, tibC, leoA, and east-1) was not associated with disease. However, east-1 was associated with LT/STh strains (P < 0.001), eatA with STh strains (P < 0.001), and tia with LT/STh strains (P < 0.001). A minor seasonal peak of ETEC infections was identified in May during the cold-dry season and coincided with the peak of rotavirus infections; this pattern is unusual for ETEC and may be important for vaccination strategies in Bolivia.

Structural characterization of CFA/III and Longus type IVb pili from enterotoxigenic Escherichia coli

The type IV pili are helical filaments found on many Gram-negative pathogenic bacteria, with multiple diverse roles in pathogenesis, including microcolony formation, adhesion, and twitching motility. Many pathogenic enterotoxigenic Escherichia coli (ETEC) isolates express one of two type IV pili belonging to the type IVb subclass: CFA/III or Longus. Here we show a direct correlation between CFA/III expression and ETEC aggregation, suggesting that these pili, like the Vibrio cholerae toxin-coregulated pili (TCP), mediate microcolony formation. We report a 1.26-Å resolution crystal structure of CofA, the major pilin subunit from CFA/III. CofA is very similar in structure to V. cholerae TcpA but possesses a 10-amino-acid insertion that replaces part of the α2-helix with an irregular loop containing a 3(10)-helix. Homology modeling suggests a very similar structure for the Longus LngA pilin. A model for the CFA/III pilus filament was generated using the TCP electron microscopy reconstruction as a template. The unique 3(10)-helix insert fits perfectly within the gap between CofA globular domains. This insert, together with differences in surface-exposed residues, produces a filament that is smoother and more negatively charged than TCP. To explore the specificity of the type IV pilus assembly apparatus, CofA was expressed heterologously in V. cholerae by replacing the tcpA gene with that of cofA within the tcp operon. Although CofA was synthesized and processed by V. cholerae, no CFA/III filaments were detected, suggesting that the components of the type IVb pilus assembly system are highly specific to their pilin substrates.

Impact of rapid urbanization on the rates of infection by Vibrio cholerae O1 and enterotoxigenic Escherichia coli in Dhaka, Bangladesh

Background

In Bangladesh, increases in cholera epidemics are being documented with a greater incidence and severity. The aim of this prospective study was to identify the prevalence and importance of V. cholerae O1 and enterotoxigenic Escherichia coli (ETEC) as causal agents of severe diarrhea in a high diarrhea prone urban area in Dhaka city.

Methodology

Systematic surveillance was carried out on all diarrheal patients admitted from Mirpur between March 2008 to February 2010 at the ICDDR, B hospital. Stool or rectal swabs were collected from every third diarrheal patient for microbiological evaluation.

Principal Findings

Of diarrheal patients attending the hospital from Mirpur, 41% suffered from severe dehydration with 39% requiring intravenous rehydration therapy. More diarrheal patients were above five years of age (64%) than those below five years of age (36%). About 60% of the patients above five years of age had severe dehydration compared with only 9% of patients under five years of age. The most prevalent pathogen isolated was Vibrio cholerae O1 (23%) followed by ETEC (11%). About 8% of cholera infection was seen in infants with the youngest children being one month of age while in the case of ETEC the rate was 11%. Of the isolated ETEC strains, the enterotoxin type were almost equally distributed; ST accounted for 31% of strains; LT/ST for 38% and LT for 31%.

Conclusion

V. cholerae O1 is the major bacterial pathogen and a cause of severe cholera disease in 23% of patients from Mirpur. This represents a socioeconomic group that best reflects the major areas of high cholera burden in the country. Vaccines that can target such high risk groups in the country and the region will hopefully be able to reduce the disease morbidity and the transmission of pathogens that impact the life and health of people.

Bangladesh is a country where acute dehydrating diarrhea or cholera is common and is seen at least two times every year and additionally in natural disasters. In addition cholera cases have increased in the country, especially in urban settings such as in the capital city, Dhaka, where the number of hospitalized patients with more severe disease has tremendously increased. In the present observation, we have concentrated on determining the occurrence of diarrhoea caused by the two most common bacterial agents V. cholerae O1 and enterotoxigenic Escherichia coli (ETEC) in a densely populated, disease prone area Mirpur in Dhaka for two years from March 2008 to February 2010. Stool or rectal specimens from diarrheal patients coming to the ICDDR,B hospital from Mirpur were tested for the two bacterial pathogens. We found that V. cholerae O1 was the major bacterial pathogen and a cause of severe cholera disease in 23% of patients (2,647 of a total of 11,395 patients) from Mirpur. We surmise that cholera vaccines, as well as other public health tools that can target such high risk groups in the country, will be able to reduce the disease morbidity and the transmission of pathogens to improve the quality of life in urban settings.

Longus, a type IV pilus of enterotoxigenic Escherichia coli, is involved in adherence to intestinal epithelial cells

Enterotoxigenic Escherichia coli (ETEC) is the leading bacterial cause of diarrhea in the developing world, as well as the most common cause of traveler's diarrhea. The main hallmarks of this type of bacteria are the expression of one or more enterotoxins and fimbriae used for attachment to host intestinal cells. Longus is a pilus produced by ETEC. These bacteria grown in pleuropneumonia-like organism (PPLO) broth at 37 degrees C and in 5% CO(2) produced longus, showing that the assembly and expression of the pili depend on growth conditions and composition of the medium. To explore the role of longus in the adherence to epithelial cells, quantitative and qualitative analyses were done, and similar levels of adherence were observed, with values of 111.44 x 10(4) CFU/ml in HT-29, 101.33 x 10(4) CFU/ml in Caco-2, and 107.11 x 10(4) CFU/ml in T84 cells. In addition, the E9034A Delta lngA strain showed a significant reduction in longus adherence of 32% in HT-29, 22.28% in Caco-2, and 21.68% in T84 cells compared to the wild-type strain. In experiments performed with nonintestinal cells (HeLa and HEp-2 cells), significant differences were not observed in adherence between E9034A and derivative strains. Interestingly, the E9034A and E9034A Delta lngA(pLngA) strains were 30 to 35% more adherent in intestinal cells than in nonintestinal cells. Twitching motility experiments were performed, showing that ETEC strains E9034A and E9034A Delta lngA(pLngA) had the capacity to form spreading zones while ETEC E9034A Delta lngA does not. In addition, our data suggest that longus from ETEC participates in the colonization of human colonic cells.

Isolation of a bacteriophage specific for CS7-expressing strains of enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is the most common bacterial cause of childhood diarrhoea in Bangladesh. Among the virulence factors of ETEC, toxins and colonization factors (CFs) play a major role in pathogenesis. Unlike Vibrio cholerae, the relationship between ETEC and ETEC-specific phages is poorly understood and the possible role of ETEC phages in the evolution of ETEC strains in the environment is yet to be established. This study was designed specifically to isolate phages that are specific for ETEC virulence factors. Among the 49 phages isolated from 12 different surface water samples, 13 were tested against 211 ETEC strains collected from clinical and environmental sources. One phage, designated IMM-001, showed a significant specificity towards CS7 CF as it attacked all the CS7-expressing ETEC. Electron microscopic analyses showed that the isolated phage possessed an isomeric hexagonal head and a long filamentous tail. An antibody blocking method and phage neutralization assay confirmed that CS7 pilus is required for the phage infection process, indicating the role of CS7 fimbrial protein as a potential receptor for IMM-001. In summary, this study showed the presence of a lytic phage in environmental water that is specific for the CS7 CF of ETEC.

Concomitant enterotoxigenic Escherichia coli infection induces increased immune responses to Vibrio cholerae O1 antigens in patients with cholera in Bangladesh

Vibrio cholerae O1 and enterotoxigenic Escherichia coli (ETEC) are major bacterial pathogens that cause dehydrating disease requiring hospitalization of children and adults. The cholera toxin (CT) produced by V. cholerae O1 and the heat-labile toxin (LT) and/or heat-stable toxin (ST) of ETEC are responsible for secretory diarrhea. We have observed that about 13% of hospitalized diarrheal patients are concomitantly infected with V. cholerae O1 and ETEC. In order to understand the outcome of such dual infections on the clinical and immunological responses in cholera patients, we studied patients infected with V. cholerae O1 (group VC; n = 25), those infected with both V. cholerae O1 and ETEC (group VCET; n = 25), and those infected with ETEC only (group ET; n = 25). The VCET group showed more severe dehydration and had a higher intake of intravenous fluid and more vomiting than the ETEC group (P = 0.01 to 0.003). The VCET patients showed higher vibriocidal responses and increased antibody titers to cholera toxin and lipopolysaccharide (LPS) in plasma than did the V. cholerae O1 patients (P = 0.02 to <0.001). All responses in the V. cholerae O1 and in the VCET groups were more robust than those seen in the group infected with ETEC only (P = 0.01 to <0.001). We thus show that concomitant colonization with ETEC induces immune responses to V. cholerae antigens that are more robust than those seen with V. cholerae O1 infection alone. It is possible that LT or other factors expressed by ETEC may play a role as a mucosal adjuvant in enhancing the immune responses to V. cholerae O1.

Genetic diversity of the gene cluster encoding longus, a type IV pilus of enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) strains produce a type IV pilus named Longus. We identified a 16-gene cluster involved in the biosynthesis of Longus that has 57 to 95% identity at the protein level to CFA/III, another type IV pilus of ETEC. Alleles of the Longus structural subunit gene lngA demonstrate a diversity of 12 to 19% at the protein level with strong positive selection for point replacements and horizontal transfer.

Comparison of enterotoxigenicEscherichia coliisolated from surface water and diarrhoeal stool samples in Bangladesh

Enterotoxigenic Escherichia coli (ETEC) is a common cause of bacterial infection leading to acute watery diarrhea in infants and young children. Although the prevalence of ETEC is high in Bangladesh and infections can be spread through food and contaminated water, limited information is available about ETEC in the surface water. We carried out studies to isolate ETEC from surface water samples from ponds, rivers, and a lake from a site close to field areas known to have a high incidence of diarrhea in Dhaka, Bangladesh, and Matlab, Bangladesh. ETEC strains isolated from the water sources were compared with ETEC strains isolated from patients with diarrhea at two hospitals in these areas. ETEC were isolated from 30% (45 of 150) of the samples from the surface water sources and 19% (518 of 2700) of the clinical specimens. One hundred ETEC strains isolated from patients with similar phenotypes as the environmental strains were compared for phenotypic and genotypic properties. The most common O serogroups on ETEC were O6, O25, O78, O115, and O126 in both types of strains. Pulsed-field gel electrophoresis analyses of the ETEC strains showed that multiple clones of ETEC were present within each colonization factor type and that some clones detected in the environment were also isolated from the stools of patients. The strains showed multiple and similar antibiotic resistance patterns. This study shows that ETEC is prevalent in surface water sources in Bangladesh suggesting a possible reason for the endemicity of this pathogen in Bangladesh.Key words: enterotoxigenic Escherichia coli (ETEC), surface water samples, colonization factors, pulsed-field gel electrophoresis, toxin types.

Enterotoxigenic Escherichia coli in developing countries: epidemiology, microbiology, clinical features, treatment, and prevention

ETEC is an underrecognized but extremely important cause of diarrhea in the developing world where there is inadequate clean water and poor sanitation. It is the most frequent bacterial cause of diarrhea in children and adults living in these areas and also the most common cause of traveler's diarrhea. ETEC diarrhea is most frequently seen in children, suggesting that a protective immune response occurs with age. The pathogenesis of ETEC-induced diarrhea is similar to that of cholera and includes the production of enterotoxins and colonization factors. The clinical symptoms of ETEC infection can range from mild diarrhea to a severe cholera-like syndrome. The effective treatment of ETEC diarrhea by rehydration is similar to treatment for cholera, but antibiotics are not used routinely for treatment except in traveler's diarrhea. The frequency and characterization of ETEC on a worldwide scale are inadequate because of the difficulty in recognizing the organisms; no simple diagnostic tests are presently available. Protection strategies, as for other enteric infections, include improvements in hygiene and development of effective vaccines. Increases in antimicrobial resistance will dictate the drugs used for the treatment of traveler's diarrhea. Efforts need to be made to improve our understanding of the worldwide importance of ETEC.

Enterotoxigenic Escherichia coli and Vibrio cholerae diarrhea, Bangladesh, 2004

Flooding in Dhaka in July 2004 caused epidemics of diarrhea. Enterotoxigenic Escherichia coli (ETEC) was almost as prevalent as Vibrio cholerae O1 in diarrheal stools. ETEC that produced heat-stable enterotoxin alone was most prevalent, and 78% of strains had colonization factors. Like V. cholerae O1, ETEC can cause epidemic diarrhea.

Prevalence of enterotoxigenic Escherichia coli strains harboring the longus pilus gene in Brazil

The longus type IV pilus gene (lngA) was highly prevalent (32.8%) among Brazilian enterotoxigenic Escherichia coli strains producing both heat-labile and heat-stable enterotoxins and bearing the CFA/I, CS1CS3, or CS6 antigen. Furthermore, lngA was more often found in strains isolated from children with diarrhea than in strains isolated from children without diarrhea.

Type IV longus pilus of enterotoxigenic Escherichia coli: occurrence and association with toxin types and colonization factors among strains isolated in Argentina

The longus type IV pilus structural gene (lngA) was sought among 217 clinical enterotoxigenic Escherichia coli (ETEC) strains isolated in Argentina. lngA was present in 20.7% of the isolates and was highly associated with ETEC producing heat-stable toxin and the most common colonization factors. The prevalence of longus among ETEC strains in Argentina was comparable to that of colonization factor antigen I (CFA/I), CFA/II, and CFA/IV in other regions of the world.

Identification of enterotoxigenic Escherichia coli harboring longus type IV pilus gene by DNA amplification

DNA amplification of lngA, the structural gene of longus type IV pilus produced by human enterotoxigenic Escherichia coli (ETEC) was achieved by the use of specific oligonucleotide primers designed from the nucleotide sequence of lngA. A 630-bp fragment representing the entire lngA gene was amplified in eight prototype strains previously characterized as longus positive. Five ETEC strains producing colonization factor antigen III (CFA III) (also a type IV pilus) were also positive by PCR, confirming the DNA homology between CFA III and longus. None of the non-ETEC and non-E. coli enteropathogens studied showed the 0.63-kbp amplicon. The procedure thus detected only ETEC strains harboring type IV pili genes with or without other colonization factors. Except for five lngA PCR-positive, probe-positive strains, all lngA PCR-positive strains produced the pilin as demonstrated by immunoblotting. To test the amplification procedure in a clinical setting, a collection of 264 fresh clinical E. coli strains isolated from 88 Mexican children with diarrhea was screened by PCR. Among 82 ETEC isolates found, 30 (36.5%) were lngA PCR-positive. Twenty-seven percent of the children shed ETEC that possessed lngA. In parallel with DNA probes or PCR protocols to detect enterotoxin genes, the lngA PCR method may prove useful for detection of ETEC harboring type IV pilus genes in epidemiological studies.