Phenotypic and Molecular Characteristics ofEscherichia coliIsolated from Aquatic Environment of Bangladesh

Pathogenic Escherichia coli remains important etiological agent of infantile diarrhea in Bangladesh. Previous studies have focused mostly on clinical strains, but very little is known about their presence in aquatic environments. The present study was designed to characterize potentially pathogenic E. coli isolated between November 2001 and December 2003 from aquatic environments of 13 districts of Bangladesh. Serotyping of 96 randomly selected strains revealed O161 to be the predominant serotype (19%), followed by O55 and O44 (12% each), and 11% untypable. Serotype-based pathotyping of the E. coli strains revealed 47%, 30%, and 6% to belong to EPEC, ETEC, and EHEC pathotypes, respectively. The majority of the 160 strains tested were resistant to commonly used antimicrobial agents. Plasmid pro-filing showed a total of 17 different bands ranging from 1.3 to 40 kb. However, 35% of the strains did not contain any detectable plasmid, implying no correlation between plasmid and drug resistance. Although virulence gene profiling revealed 97 (61%) of the strains to harbor the gene encoding heat-stable enterotoxin (ST), 2 for the gene encoding Shiga toxin (Stx), and none for the gene for heat-labile enterotoxin (LT), serotype-based pathotyping of E. coli was not fully supported by this gene profiling. A dendrogram derived from the PFGE patterns of 22 strains of three predominant serogroups indicated two major clusters, one containing mainly serogroup O55 and the other O8. Three strains of identical PFGE profiles belonging to serogroup O55 were isolated from three distinct areas, which may be of epidemiological significance. Finally, it may be concluded that serotype-based pathotyping may be useful for E. coli strains of clinical origin; however, it is not precise enough for reliably identifying environmental strains as diarrheagenic.

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.

Genetic control and properties of coli surface antigens of colonization factor antigen IV (PCF8775) of enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli producing coli surface antigen 4 (CS4), CS5, and CS6 of colonization factor antigen IV were examined. This factor was originally called putative colonization factor 8775 (PCF8775). All of the coli surface antigens were plasmid coded and were usually carried on the same plasmid as the genes coding for heat-stable toxin (ST) or heat-labile toxin (LT); thus, CS5-CS6-ST, CS6-ST, and CS6-LT plasmids were found. In strains of serotype O25:H42, the genes coding for CS4 and CS6 were on a plasmid separate from that containing the genes coding for ST and LT. CS4 and CS5 were fimbrial antigens with a subunit molecular mass of about 17.0 and 21.0 kilodaltons (kDa), respectively. CS6 was found as a single polypeptide with a molecular mass of about 14.5 kDa in strains of serotypes O25:H42, O27:H7, and O27:H20 when heated extracts were run on sodium dodecyl sulfate-polyacrylamide gels. CS6-positive extracts of strains of serogroups O148, O159, and O167 showed two bands with molecular masses between 14.5 and 16.0 kDa.

[Direct detection in diarrheal stools of Escherichia coli adhesion factors CFA/I, CFA/II and E8775 by the india ink immune reaction]

An India ink immune reaction was used for the direct detection, in diarrhoeal stools, of Escherichia coli possessing the CFA/I, CFA/II and E8775 fimbriae. With this method, a presumptive diagnosis of enterotoxigenic E. coli (ETEC) can rapidly be made. Staining required the bivalency of rabbit anti-fimbriae IgG; the F(ab')2 fragment was necessary. The reaction was impossible with purified Fab fragment. A comparative study of this technique and detection by culture of ETEC strains showed good correlation when the India ink immune reaction was performed at the beginning of infection.

Escherichia coli diarrhoea

Ever since Escherich (1885) first isolated the organism now known asEscherichia colifrom the stools of infants, medical microbiologists have been faced with the problem of distinguishing between those strains capable of causing diarrhoea and those that are harmless gut commensals. Epidemiological investigations were greatly facilitated by the description by Kauffmann (1947) of a serotyping scheme forE. coli, and Taylor (1961) later reported that 17 0 serogroups ofE. colihad been implicated as possible causes of epidemic infantile enteritis. These infantile enteropathogenicE. coli(EPEC), having been discovered by epidemiological studies using serotyping, belonged by definition to a restricted range of serogroups. More recently it was shown that otherE. colistrains may produce enterotoxins, and these enterotoxigenicE. coli(ETEC) usually belong to particular serogroups which are different from those associated with EPEC.E. colistrains belonging to a third range of serogroups may cause an illness resembling shigella dysentery, and these may be regarded as entero-invasiveE. coli(EIEC).E. colistrains that cause diarrhoea may therefore be considered as three groups, as follows.

ST:LT:CFA/II plasmids in enterotoxigenic Escherichia coli belonging to serogroups O6, O8, O80, O85, and O139

Colonization factor antigen II-producing enterotoxigenic Escherichia coli serotypes possessed at least one large plasmid. Loss of colonization factor antigen II correlated with either complete or partial loss of the large plasmid. Complete loss of the plasmid always correlated with complete loss of enterotoxin production. Three of five deletion events also correlated with the loss of toxin production.

CFA/I-ST plasmids: comparison of enterotoxigenic Escherichia coli (ETEC) of serogroups O25, O63, O78, and O128 and mobilization from an R factor-containing epidemic ETEC isolate

Colonization factor antigen I (CFA/I) plays an important role in the pathogenesis of diarrhea due to enterotoxigenic Escherichia coli. In this study, we examined 11 CFA/I+ enterotoxigenic E. coli from serogroups O25, O63, O78, and O128 and found that with all strains, spontaneous loss of CFA/I was associated with the loss of heat-stable toxin (ST) and with the loss of a single plasmid ranging in size from 54 to 60 megadaltons; when heat-labile toxin was lost, this was associated with the loss of another plasmid. The R factor of one strain, TX432 (O78:H12:CFA/I+; ST+), was found to mobilize the CFA/I-ST plasmid into E. coli K-12 at a frequency of 20%. These studies provide further evidence that CFA/I production is plasmid mediated in enterotoxigenic E. coli belonging to serogroups O25, O63, O78, and O128.

Correlation between intestinal immune response to colonization factor antigen/I and acquired resistance to enterotoxigenic Escherichia coli diarrhea in an adult rabbit model

Immunoprotection against diarrhea caused by colonization factor antigen/I (CFA/I)-positive, human-associated, enterotoxigenic Escherichia coli was investigated using the adult rabbit intestinal temporary ligation technique. An oral dose of 1 X 10(8) viable cells of enterotoxigenic Escherichia coli strain H-10407 (078:H11:CFA/I) produced diarrhea in all animals challenged. Rabbits allowed to survive this challenge dose were re-challenged approximately six weeks later with the result that four of seven (57%) did not develop diarrhea. Peroral immunization of rabbits with purified CFA/I elicited protection against challenge with strain H-10407; this protection was dose-related and CFA/I-specific. Immunoprotection did not correlate with a systemic antibody response. CFA/I produced a relatively poor immune response in terms of the number of IgM- and IgG-producing cells in the lamina propria of the animals but did elicit a vigorous increase in the number of intestinal IgA- and anti-CFA/I-producing cells. There was a highly significant inverse relationship between the number of IgA- and anti-CFA/I-producing cells in the lamina propria of the rabbits and the diarrhea response to the challenge strain H-10407 (correlation coefficients of -0.616 and -0.678 respectively). It is concluded that anti-CFA/I antibody, probably of the IgA class, is the major immune response to orally administered CFA/I and that this response is highly immunoprotective.

Plasmids coding for enterotoxins, K88 antigen and colicins in porcine Escherichia coli strains of O-group 149

This study was carried out to determine whether the strong epidemiological correlation observed in Sweden between production of the adhesin K88, the heat-stable (ST) and the heat-labile (LT) enterotoxins in E. coli strains of O-group 149 isolated from piglet diarrhea might be explained by linkage of their genetic determinants. From 22 different isolates plasmids coding for these virulence factors were investigated by conjugation and transduction experiments and analysis on agarose gels. The genes coding for ST production could be transferred by selection for antibiotic resistance, but behaved as transposable elements most often residing on a 55 Mdal plasmid coding for colicin B. The genes coding for raffinose fermentation and K88 antigen production were located on a 45 Mdal plasmid and the genes coding for LT production on plasmids within the 45-70 Mdal size. Thus the epidemiological importance and spread of this O-group in Sweden was explained by its stable content of two or three virulence plasmids, which could be transferred independently of one another.