EFFECT OF NONTARGET CELLS ON THE SENSITIVITY OF THE PCR FOR ESCHERICHIA-COLI O157-H7

The sensitivity of a multiples PCR for the virulence factors VT1, VT2 and eaeA specific for enterohaemorrhagic Escherichia coli (target cell s, T) was adversely affected when non-pathogenic E. coli (non-target, NT) cells were present. In the absence of NT cells the sensitivity, ob tained by decimally diluting the T cell culture, was T-10 (<10 cfu ml( -1)) for eaeA and VT2, and T-5 (Ca 10(4) cfu ml-(1) T) for VTL virulen ce factors. When approximately 10(9) cfu ml(-1) NT cells (NTO dilution ) were present, the sensitivity dropped to T-2, T-3 and T-1 (ca 10(7), 10(6) and 10(8) cfu ml(-1) T) for eaeA, VT2 and VT1, respectively. At NT-1 (ca 10(8) cfu ml(-1) NT) or higher dilutions the sensitivity of eaeA and VT2 was the same as when no NT cells were present. In respect of VT1 the sensitivity gradually increased until at NT-4 the sensitiv ity was the same as when NT cells were completely absent. This work in dicates that caution should be exercised when interpreting PCR results particularly when substantial non-target cell populations are suspect ed.