[Incidence and prevalence of serotypes of enteroaggregative Escherichia coli from diarrheal patients in Brazil, Myanmar and Japan]

Genetic elements associated with antimicrobial resistance in enteropathogenic Escherichia coli (EPEC) from Brazil

Background

We recently observed an association of resistance with a certain enteropathogenic Escherichia coli (EPEC) serotypes and identified a conjugative plasmid, similar to plasmid pED208, that was conserved among archival O111:H2/NM and O119:H2 strains of diverse geographical origin. In this study, we sought to determine the prevalence and distribution of this plasmid among a collection of EPEC isolates from Brazil, as well as to study the susceptibilities of these isolates to antimicrobial agents.

Results

Resistance was more commonly seen in typical EPEC than atypical strains. The most prevalent resistances were to ampicillin, tetracycline, streptomycin and the sulfonamides. Markers for the EPEC conjugative multiresistance plasmid, were detected in 21 (30%) of typical but only 4 (5%) of atypical strains (p = 0.001, Chi-squared test). This plasmid, previously reported from only O111 and O119 strains was found in O55 and O127 strains and was associated with the presence of class 1 integrons.

Conclusion

Our data suggest a limited but expanding host range for the EPEC resistance plasmid.

The commonly-used DNA probe for diffusely-adherent Escherichia coli cross-reacts with a subset of enteroaggregative E. coli

Background

The roles of diffusely-adherent Escherichia coli (DAEC) and enteroaggregative E. coli (EAEC) in disease are not well understood, in part because of the limitations of diagnostic tests for each of these categories of diarrhoea-causing E. coli. A HEp-2 adherence assay is the Gold Standard for detecting both EAEC and DAEC but DNA probes with limited sensitivity are also employed.

Results

We demonstrate that the daaC probe, conventionally used to detect DAEC, cross-reacts with a subset of strains belonging to the EAEC category. The cross hybridization is due to 84% identity, at the nucleotide level, between the daaC locus and the aggregative adherence fimbriae II cluster gene, aafC, present in some EAEC strains. Because aaf-positive EAEC show a better association with diarrhoea than other EAEC, this specific cross-hybridization may have contributed to an over-estimation of the association of daaC with disease in some studies. We have developed a discriminatory PCR-RFLP protocol to delineate EAEC strains detected by the daaC probe in molecular epidemiological studies.

Conclusions

A PCR-RFLP protocol described herein can be used to identify aaf-positive EAEC and daaC-positive DAEC and to delineate these two types of diarrhoeagenic E. coli, which both react with the daaC probe. This should help to improve current understanding and future investigations of DAEC and EAEC epidemiology.

Molecular epidemiological characteristics of virulence factors on enteroaggregative E. coli

Escherichia coli with various types of adherence patterns to cultured epithelial cells have been described over the years as being associated with both acute and persistent diarrhea. Most enteroaggregative E. coli (EAEC) strains harbor a 60- to 65-MDa plasmid called pAA which has been shown to encode the aggregative adherence fimbriae AAF/I and AAF/II; the enterotoxin EAST1 and Pet, a serine protease which has been described as causing enterotoxic and cytotoxic effects. Another serine protease denominated Pic, encoded by a chromosomal gene displaying mucinolytic activity, serum resistance, and hemagglutination, has also been associated with EAEC strains. In this study, EAEC strains that isolated from the rectal swab of neonates at the neonatal intensive care unit of Pusan National University Hospital in 2003 were tested for the presence of the pAA using polymerase chain reaction (PCR) and DNA colony hybridization methods. To further characterize these EAEC strains, we used PCR to detect genes for proposed EAEC virulence factors and examined HeLa cell adherence assay, antimicrobial susceptibility test, serotyping, cytotoxicity test and epidemiological characteristics. EAEC isolates found were genotyped by random amplified polymorphic DNA and pulsed-field gel electrophoresis.

Contact hemolysin production by strains of enteroaggregative Escherichia coli isolated from children with diarrhea

Forty-five strains of enteroaggregative Escherichia coli were tested for hemolytic activity with different culture media and erythrocytes from different species. Thirty-seven strains showed proteinase K-sensitive contact hemolysin activity with sheep erythrocytes when cultured in Casamino Acids-yeast extract broth supplemented with 1 mM calcium chloride and when cultured in nutrient broth media. The production of contact hemolysin was dependent on temperature, pH, and culture conditions.