SPORADIC ISOLATES OF ESCHERICHIA-COLI O157.H7 INVESTIGATED BY PYROLYSIS MASS-SPECTROMETRY

Thirty-six encoded isolates of Escherichia coli, 32 of which were of s erotype 0157, were examined by pyrolysis mass spectrometry (PyMS). Thi rty-one of the serotype 0157 isolates possessed the flagellar antigen H7 and produced Verocytotoxin (VT), the other isolate serotyped as H45 and was non-toxigenic. Eighteen of the VT-producing E. coli (VTEC) is olates were from sporadic disease in residents of the Northern Region. Standard principal component (PC) and canonical variate (CV) analysis of the data distinguished only the four non-0157 isolates from the re mainder which were indistinguishable by this approach. A similarity ma trix based on differences between individual CV means distinguished a further ten isolates. The matrix correctly clustered 2 pairs of isolat es from siblings and 4 isolates from an affected family. A further 5 c lusters of 3 or more isolates and 6 pairs of isolates were defined. Th ese groupings proved to be homogenous for toxin phenotype but occasion ally entrained isolates of dissimilar phage type. However, in general, PyMS-derived clustering of apparently sporadic isolates accorded with geographical locations as determined by postcode. PyMS, which is a qu ick and high volume capacity phenotypic technique, may be a useful add ition to existing methods in the investigation of the epidemiology of sporadic VTEC disease.