Detection of enteric pathotypes of Escherichia coli by hybridization using six DNA probes.

A set of 6 DNA probes was tested to evaluate the incidence of various Escherichia coli pathotypes among 540 strains isolated in France from diarrhoeal stools of infants, children and adults. Enterotoxigenic E. coli were detected using 3 gene probes for enterotoxins LT, STaH and STaP. Enteroinvasive E. coli were detected using one DNA probe which specifically hybridizes with bacteria expressing the cell invasion phenotype "INV". They represented 1.5% and 1.1% of the total, respectively. An SLTI probe which contains the structural gene for the A subunit of Shiga-like toxin I was constructed to detect enterohaemorrhagic E. coli. Among the 5 strains detected, only 1 belonged to serotype O157:H7. An attempt was made to detect enteropathogenic E. coli (EPEC) using both an EPEC-adherence factor and the above mentioned SLTI probes. Under the experimental conditions, they did not appear to be efficient at detecting this pathotype.

Presence and expression of aerobactin genes in virulent avian strains of Escherichia coli.

Virulent and nonvirulent isolates of avian Escherichia coli were tested for the presence of aerobactin genes by colony hybridization with a specific gene probe constructed from plasmid pABN1 (A. Bindereif and J. B. Neilands, J. Bacteriol. 153:1111-1113, 1983). Positive hybridization with the gene probe was highly correlated with virulence, as measured by the 50% lethal dose of the strains for chicks. Evidence for the expression of aerobactin genes in the virulent strains was obtained by demonstrating their susceptibility to cloacin DF13, which binds to the same receptor that binds aerobactin, and their ability to produce aerobactin, as revealed by cross-feeding the E. coli mutant WO987 (aroB fepA iuc iut+), which is unable to synthesize but capable of taking up aerobactin. We suggest that the production of aerobactin is involved in the virulence of avian septicemic E. coli.

DNA hybridization technique to detect Shigella species and enteroinvasive escherichia coli.

A DNA hybridization method for the detection of Shigella species and enteroinvasive Escherichia coli is described. It is based upon the high degree of homology shared by the virulence plasmids present in all pathogenic strains. After 32P labeling, a 17-kilobase EcoRI restriction fragment of a virulence plasmid belonging to Shigella flexneri serotype 5 was used as a probe to detect Shigella species and enteroinvasive E. coli in isolated colonies. This method proved highly specific as well as sensitive and should be particularly useful for the characterization of atypical isolates and for large-scale epidemiological studies in endemic areas.