Expression of cytotoxicity by potential pathogens in the standard Escherichia coli collection of reference (ECOR) strains.
The standard Escherichia coli collection of reference (ECOR) strains was examined for ability to exert cytotoxicity towards mammalian cells. A group of strains with functional haemolysin expression caused strong cytotoxicity and detachment in J774 macrophage cells as measured by lactate dehydrogenase release and as observed under a microscope. The expression of haemolysin was monitored by using antisera recognizing the E. coli alpha-haemolysin, the HlyA protein, and by quantitative haemolysis assays. The presence of the hlyA gene, which may be part of a pathogenicity island, was also confirmed. These analyses revealed that different ECOR strains express quantitatively different levels of haemolysin. One putative enteroaggregative E. coli (EAEC) strain was also found in the ECOR collection. The EAEC strain was characterized by the clump formation assay, PCR amplification of the EAEC DNA probe sequence and confirmative sequence analysis of the amplified fragment. The EAEC heat-stable enterotoxin 1 gene, astA, was found in 14% (10/72) of the ECOR strains and a consensus sequence for astA was proposed by comparing these sequences with those from pathogens. The astA gene appeared to be plasmid-located. Based on evidence from the work of other laboratories and from the present findings, it is concluded that the ECOR collection contains strains that may represent pathogenic E. coli. It is noted that caution is necessary when handling or disposing of those potentially pathogenic ECOR strains.
Lai
Xin-He
XH
Department of Microbiology, Umeå University, Umeå S-90187, Sweden1.
Wang
Su-Yan
SY
Department of Microbiology, Umeå University, Umeå S-90187, Sweden1.
Uhlin
Bernt Eric
BE
Department of Microbiology, Umeå University, Umeå S-90187, Sweden1.
D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D015153:Blotting, Western; D002460:Cell Line; D016384:Consensus Sequence; D004926:Escherichia coli / Q000201:enzymology* / Q000472:pathogenicity; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D005838:Genotype; D006460:Hemolysin Proteins / Q000235:genetics / Q000378:metabolism*; D006736:Horses; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction
D001426:Bacterial Proteins; D001427:Bacterial Toxins; D029968:Escherichia coli Proteins; D006460:Hemolysin Proteins; C036507:Hlya protein, E coli