A comparative study of clinical and food isolates ofListeria monocytogenesand related species

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Abstract
SUMMARY: Ninety-six isolates of presumptive or confirmedListeria monocytogeneswere obtained from local clinical (30 isolates) or food laboratories (66 isolates). Minimal biochemical analysis identified only 80% of these isolates asL. monocytogenesthe remaining includedL. seeligeri, 1%, or the non-haemolyticL. innocua, 19%. The 27 clinical and 50 food isolates, mainly from meat products, frozen confectionaries, and cheeses, confirmed asL. monocytogeneswere compared biochemically and serologically. Twenty-one isolates, including some strains ofL. innocuaandL. seeligeri, were examined for pathogenicity in immunocompromized mice and 44 typed using bacterial restriction endonuclease DNA analysis (BRENDA). Only isolates ofL. monocytogeneswere found to be pathogenic. Biovar-typing of the isolates was unreliable and provided poor discrimination. Serogroups 1/2 and 4 predominated among clinical and food isolates and BRENDA provided better discrimination among isolates. Ten stable and reproducible restriction patterns were observed among theListeriasp. isolates studied. Overall, a combination of techniques gave the best discrimination and indicated their potential for use as epidemiological tools.