Expression of cytotoxicity by potential pathogens in the standard Escherichia coli collection of reference (ECOR) strains The GenBank accession numbers for the sequences reported in this paper are AF159702 and AF160993–161002.

Abstract

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 α-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.

An Escherichia coli Reference Collection Group B2- and Uropathogen-Associated Polymorphism in the rpoS-mutS Region of the E. coli Chromosome

“…PCR test 1 (Table 1) detected this sequence in ECOR strains EC23 and EC32 and in each of the ECOR group B2 strains. UTI-related virulence determinants, believed to have arrived by horizontal gene transfer, occur at higher frequency within ECOR group B2 than among other ECOR strains (Table 3) (6,20,22). The presence of the rpoS-proximal 2.1-kb insertion within group B2 members is therefore consistent with its presence in many UTI isolates (Table 1).…”

Occurrence of hlyA and sheA Genes in Extraintestinal Escherichia coli Strains

“…No E. coli K-12 strains tested carried the hlyA gene. Nine members of the ECOR collection carried the hlyA gene, supporting results of a previous study (15), while 198 extraintestinal clinical isolates and only 8 normal fecal isolates carried hlyA. The sheA gene was identified in all tested K-12 strains, 55 of the ECOR strains, 241 of the extraintestinal clinical isolates, and 94 of the fecal isolates from healthy individuals (Table 3).…”

Detection of Diarrheagenic Escherichia coli by Use of Melting-Curve Analysis and Real-Time Multiplex PCR

“…They had originally been isolated from healthy individuals or from women with urinary tract infections (ECOR strains 11, 14, 40, 48, 50, 56, 60, 62, 64, 71, and 72). Three of the ECOR strains are known to have virulence genes that have been associated with illness: ECOR 8 is an EAEC strain on the basis of its adherence pattern and its aggregative-adherence-probe positivity (12); ECOR 50 and ECOR 64 are known to be PCR positive for afa and draBC, markers of Dr adhesin-positive strains, including DAEC strains, as well as some urinary tract pathogens (11). Thus, these three strains were included with the pathogens as EAEC, DAEC, and DAEC, respectively, rather than being considered commensals.…”