Multiplex PCR analysis of pure cultures of nontoxigenic
E. coli O157:H7 strain 3704 revealed three distinct bands of
expected size, corresponding to H7, intimin and O157
(Fig. 1). No PCR amplicons of the expected size were
observed for Shiga-like toxin I and Shiga-like toxin II genes
con®rming previous data on the absence of toxin genes
(by PCR) in this strain (F. Thomson-Carter, unpublished
observation).