Studies on Escherichia coli as a cause of acute diarrhoea in Calcutta

Part III. Analysis of data gaps pertaining to enterotoxigenic Escherichia coli infections in low and medium human development index countries, 1984-2005

Enterotoxigenic Escherichia coli (ETEC) is a common cause of profuse watery diarrhoea in the developing world, often leading to severe dehydration or death. We found only 15 population-based studies in low and medium human development index (HDI) countries from 1984 to 2005 that evaluate disease incidence. Reported incidence ranged from 39 to 4460 infections/1000 persons per year. The peak incidence of ETEC appeared to occur between ages 6 and 18 months. A median of 14% (range 2-36%) of diarrhoeal specimens were positive for ETEC in 19 facility- and population-based studies conducted in all age groups and 13% (range 3-39%) in 51 studies conducted in children only. Heat-labile toxin (LT)-ETEC is thought to be less likely to cause disease than heat-stable toxin (ST)-ETEC or LT/ST-ETEC. Because population-based studies involve enhanced clinical management of patients and facility-based studies include only the most severe illnesses, reliable data on complications and mortality from ETEC infections was unavailable. To reduce gaps in the current understanding of ETEC incidence, complications and mortality, large population-based studies combined with facility-based studies covering a majority of the corresponding population are needed, especially in low-HDI countries. Moreover, a standard molecular definition of ETEC infection is needed to be able to compare results across study sites.

Part II. Analysis of data gaps pertaining to Shigella infections in low and medium human development index countries, 1984-2005

The global incidence of Shigella infection has been estimated at 80-165 million episodes annually, with 99% of episodes occurring in the developing world. To identify contemporary gaps in the understanding of the global epidemiology of shigellosis, we conducted a review of the English-language scientific literature from 1984 to 2005, restricting the search to low and medium human development countries. Our review yielded 11 population-based studies of Shigella burden from seven countries. No population-based studies have been conducted in sub-Saharan Africa or in low human development countries. In studies done in all age groups, Shigella incidence varied from 0.6 to 107 episodes/1000 person-years. S. flexneri was the most commonly detected subgroup in the majority of studies. Case-fatality rates ranged from 0% to 2.6% in population-based studies and from 0% to 21% in facility-based studies. This review highlights the large gaps in data on the burden of Shigella infections for low human development index countries and, more specifically, for sub-Saharan Africa.

Investigation of diarrhoeic faecal samples for enterotoxigenic, Shiga toxin-producing and typical or atypical enteropathogenic Escherichia coli in Kashmir, India

Three hundred and twenty-six Escherichia coli isolates recovered from 326 human faecal specimens from sporadic cases of diarrhoea in Kashmir valley, India, were investigated for the presence of stx(1), stx(2), eaeA, hlyA and lt virulence genes. None of the samples was positive for stx genes or Shiga toxins by PCR or enzyme-linked immunosorbent assay. Twenty-three E. coli isolates showed the presence of the eaeA gene, whereas three isolates harboured the lt gene. Enteropathogenic E. coli (EPEC) belonged to 10 different serogroups. Out of 23 EPEC isolates, the majority (78.26%) were atypical while five (21.73%) were typical. Only one of the typical EPEC harboured the EAF plasmid. Subtyping of the eaeA gene showed the presence of eaeA-alpha(1), eaeA-beta, eaeA-xi and eaeA-eta in one, two, four and two isolates, respectively. None of the E. coli isolates possessed eaeA-delta, eaeA-epsilon and eaeA-zeta. This study further upholds the opinion that Shiga toxin-producing E. coli do not pose a major threat to human health in India and eaeA-alpha(1), eaeA-beta, eaeA-xi and eaeA-eta could be common EPEC subtypes prevalent in humans with diarrhoea in India. The present study appears to be the first report of subtype analysis of the eaeA gene from India and also records the isolation of EPEC with the eaeA-xi gene from humans.

Occurrence, distribution, and associations of O and H serogroups, colonization factor antigens, and toxins of enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is a leading cause of infectious diarrhea worldwide. Four categories of antigens have been commonly studied: O serogroup, H serogroup, colonization factor antigens (CFA), and toxins. A database has been complied from published reports of nearly 1,000 ETEC isolates from 18 locations and analyzed to determine the occurrence, distribution, and associations of O serogroup, H serogroup, CFA, and toxin type. Tables listing the associations of antigens are presented. This analysis documents the widespread nature and variety of ETEC. Even the most common combination of antigens, O6:H16 CFA/II LTST, accounted for only 11% of the ETEC isolates in the database. It was isolated from 12 locations. Many phenotypes occurred only once. CFA detection based on enzyme-linked antibodies with polyclonal sera is suggested as the preferred assay. A combination of CFA and toxin-based antigens is suggested as the most practical vaccine.

Enterotoxigenic Escherichia coli associated diarrhoea among infants aged less than six months in Calcutta, India

The role of enterotoxigenic Escherichia coli (ETEC) as etiologic agents of diarrhoea in infants aged less than six months was assessed in a hospital based study in Calcutta, India. Of the 218 cases examined, ETEC strains were isolated from 26 (11.9%) cases. Among these, in 17 cases ETEC was the sole infecting pathogen (p = 0.0085). Of the 26 isolates (each isolate representing a case), 24 were distributed among seven different O:K:H serotypes and two different colonization factor antigens (CFAs) I and II. Two of the remaining isolation were untypable, non-haemagglutinating, and were non-hydrophobic as measured by the salt aggregation test (SAT). Of the 26 ETEC strains detected, 15 (57.7%) produced heat-labile toxin (LT) only, 8 (30.8%) liberated heat-stable toxin (ST) only, and the remaining 3 (11.5%) produced both LT and ST. No ETEC strain was isolated from the 102 age-matched controls included in this study. All the ETEC isolates were multiple drug resistant. The study showed that the diarrhoea due to ETEC was of brief duration, mostly within the range of 3 to 7 days.

Colonization factors of diarrheagenic E. coli and their intestinal receptors

While Escherichia coli is common as a commensal organism in the distal ileum and colon, the presence of colonization factors (CF) on pathogenic strains of E. coli facilitates attachment of the organism to intestinal receptor molecules in a species- and tissue-specific fashion. After the initial adherence, colonization occurs, and the involvement of additional virulence determinants leads to illness. Enterotoxigenic E. coli (ETEC) is the most extensively studied of the five categories of E. coli that cause diarrheal disease, and has the greatest impact on health worldwide. ETEC can be isolated from domestic animals and humans. The biochemistry, genetics, epidemiology, antigenic characteristics, and cell and receptor binding properties of ETEC have been extensively described. Another major category, enteropathogenic E. coli (EPEC), has virulence mechanisms, primarily effacement and cytoskeletal rearrangement of intestinal brush borders, that are distinct from ETEC. An EPEC CF receptor has been purified and characterized as a sialidated transmembrane glycoprotein complex directly attached to actin, thereby associating CF-binding with host-cell response. Three additional categories of E. coli diarrheal disease, their colonization factors and their host cell receptors, are discussed. It appears that biofilms exist in the intestine in a manner similar to oral bacterial biofilms, and that E. coli is part of these biofilms as both commensals and pathogens.

Characterization of enterotoxigenic Escherichia coli isolated from U.S. troops deployed to the Middle East

Enterotoxigenic Escherichia coli (ETEC) was a common cause of traveler's diarrhea in U.S. soldiers in the Middle East in 1989 and 1990. To determine which bacterial components would be useful in a vaccine, potential protective antigens (toxin, colonization factor antigen [CFA], and serotype) from 189 ETEC isolates were examined. Nearly half of the isolates expressed both ETEC toxins, 39% had only heat-stable enterotoxin (ST), and 17% had heat-labile enterotoxin (LT). CFA/I was the least common colonization factor antigen (11%), CFA/II was common (34%), as was CFA/IV (31%), and 24% expressed none of these CFAs. Fifty-seven O:H serotypes were found. Serotype O6:H16 was the most common, occurring in 29% of the ETEC isolates, usually with LT-ST and CFA/II. Generally, CFA/II was associated with expression of both toxins, CFA/IV was associated with expression of ST, and none of the CFAs was routinely found with LT. We conclude that ETEC from soldiers in the Middle East expressed a variety of antigens and that an effective vaccine will require multiple protective antigens.

Serovars of multi-antibiotic resistant Escherichia coli from the freshwater environs of Calcutta, India

For a period of one year (March 1987 to February 1988), the incidence of Escherichia coli was determined in water, sediment and plankton collected from two sampling sites in a freshwater lake extensively used by humans and animals. Densities of E. coli associated with plankton was the lowest while sediments, especially at site 2, harbored high densities of the organism. Correlation coefficients revealed that the density of E. coli in water samples was linearly correlated to temperature, pH of water, sediment and humidity. Stepwise multiple regression analysis, however, showed that sediment temperature was the dominant variable which could explain 27% of the observed variation in the numbers of E. coli in the overlying waters (p = less than 0.001). Of the 150 environmental E. coli strains which were characterized, 31 (20.7%) were found to belong to the classic enteropathogenic E. coli (EPEC) serogroups. Seven of the serogroups among the environmental EPEC strains were also encountered from EPEC strains isolated from human cases during a concurrent clinical study. None of the 150 environmental strains were enterotoxigenic or enteroinvasive but 4 strains possessed HEp-2 cell adhesive factor. With the exception of one, all the EPEC strains isolated were multi-drug resistant. From this study, it was evident that the lake is an important source of infection of EPEC and other related diarrheagenic E. coli.

The aetiology of diarrhoea in children at an urban hospital in Bangladesh

Enteric pathogens were studied in 104 cases with acute diarrhoea and in 74 age and sex matched concurrent controls. One or more pathogens were isolated from 59.1% of cases compared with 20.4% of controls (P less than 0.001). Single enteropathogens were detected in 33.7% and multiple enteropathogens in 25.4% of the cases. Enteropathogenic Escherichia coli (EPEC), Campylobacter jejuni, rotavirus, Vibrio cholerae non-O1 and enterotoxigenic Escherichia coli were the major pathogens detected. The high rate of isolation of EPEC from diarrhoea cases (23.1%) indicated a definite role for this pathogen in causing endemic diarrhoea in Bangladesh.