Enteropathogenic Escherichia coli (EPEC) are subdivided into “typical (t) EPEC” producing the “Bundle Forming Pili” (BFP) type 4 fimbriae and isolated from humans, and “atypical (a) EPEC” not producing the BFP and isolated from animals and humans. aEPEC are indeed quite frequently associated with diarrhoea in young calves. Though calf aEPEC can belong to the O26:H11 serotype, most serotypes remain unidentified.
The general purpose of this work is to identify the serotypes of aEPEC isolated from diarrhoeic calves in order to compare them with bovine and human Shiga toxin-producing E. coli (STEC) belonging to the same serotypes.
In two previous studies the O26:H11 and the O80:H2 serotypes were already identified by PCR in ca. 60% of the 102 aEPEC isolated between 2008 and 2015 from diarrhoeic calves at ARSIA. More recently other serogroups (O123/186, O146, O156, O177, O182, O183) were identified by PCR in 5 aEPEC and STEC that previously tested negative. The specific purpose of the study reported here was therefore to test the 41 untyped aEPEC for those six serogroups using multiplex PCR at first and to confirm the positive results with the uniplex PCRs. For comparison 35 STEC belonging to still unidentified serogroups were included in the study.
Twenty-four aEPEC tested positive (56%): 9 for the O123/186 serogroups (these two serogroups cannot be distinguished by PCR), one for the O156 serogroup, 12 for the O177 serogroup, and 2 for the O182 serogroup. In addition, the PCR also detected 8 STEC (23%): one for the O123/186, two for the O156, one for the O177 serogroups and 2 for the O182 and O183 serogroups.
The further steps of this work will investigate the following question: are the calf aEPEC true aEPEC, or STEC derivatives that have lost stx genes, or STEC precursors that could acquire stx genes in the future?