Analysis of epidemic and sporadic strains of Listeria monocytogenes by pyrolysis mass spectrometry

Twenty-six cultures of Listeria monocytogenes , serovar 4b, including 10 from a food-borne outbreak in Switzerland and sporadic patient and food isolates from both Switzerland and the UK, were compared by pyrolysis mass spectrometry (PMS). This clustered all of the Swiss epidemic isolates with four other isolates indistinguishable from the Swiss strain by phage typing, a phage non-typable isolate from a Swiss patient not known to be part of the epidemic and two strains (both from Switzerland) of a different phage type. The eight strains excluded from the PMS-derived cluster were all either known to be unrelated to the epidemic, or of a phage type distinct from the epidemic strain, or both.