Extended-spectrum β-lactamase, shigatoxin and haemolysis capacity of O157 and non-O157 E. coli serotypes from producer-distributor bulk milk

We investigated for virulence genes (stx1, stx2 and hlyA), serotypes and extended-spectrum β-lactamases (ESBLs) producing capacity in O157 and non-O157 Escherichia coli isolated from producer-distributor bulk milk (PDBM). Fifteen different E. coli O-serogroups were observed from the isolates (n = 121). The prevalence of stx1 and stx2 genes among the E. coli isolates was 8.3% and 11.6%, respectively, while 5.8% harboured both stx1 and stx2. Four E. coli isolates (3.3%) had ESBLs producing capacity, resisted multiple cephalosporins and aztreonam, and carried stx genes. Cluster analysis using GTG5 finger printing revealed a diversity of E. coli seropathotypes in PDBM that are known to be associated with human diarrhoeal diseases. These results highlight a potential risk posed on human health by the consumption of PDBM contaminated with pathogenic E. coli. A further quantitative risk assessment of the impact of pathogenic E. coli contamination in PDBM on human health is therefore recommended.