The isolation of verocytotoxin-producing Escherichia coli (VTEC) strains from improperly pasteurised cow’s milk samples

The authors investigated the possibility of the presence of VTEC strains in improperly pasteurized milk samples. A total of 64 Escherichia coli strains were isolated from 135 pasteurized milk samples originating from the same producer. The examined isolates contained 29 haemolysin-, 9 colicin- and 5 aerobactin-producing strains, but the investigations concerning heat-resistant and heat-sensitive toxins gave negative results.Six O128-type E. coli strains exerted a cytotoxic effect on the VERO cell line; 5 of them contained H12 antigen, while one could not be typed. Four of the 6 verocytotoxin-producing strains belonged in phage group 20, one in phage group (2)3(7), and one in phage group 4; four strains were of B3, one of A1, and one of A1(A2) phage type.Because of a technical failure the milk was pasteurized at 69 °C for 15 s, which is 2 °C less than required. The results underline the importance of the appropriate pasteurization temperature, as otherwise the milk may contain verocytotoxin-producing E. coli, which is a potentially great hazard for public health