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The project concerns the physiology of food poisoning microorganisms. A study is made of the physiological, biochemical and genetic basis of the organisms survival of, and responses to, food-relevant stresses and the factors influencing infectivity and toxigenesis. Low temperature ('cold shock') survival of Listeria monocytogenes has been investigated and the studies are relevant to the survival and growth of Listeria in chill-stored foods. Escherichia coli and L. monocytogenes develop resistance to otherwise lethal low pH values when first exposed to higher, non-lethal, acid pH. Also, cells grown at low growth rates become more acid-tolerant; this is of relevance to the safety of low pH processed and stored foods. The responses of L. monocytogenes to high salt and low pH stresses have been determined under conditions relevant to (Portuguese) cheese manufacture. This will provide guidance for the safe production and storage of cheeses in which L. monocytogenes is detectable. Growth temperature has been shown to result in changes to the fatty acid composition of cells of psychrophilic Clostridium botulinum; the changes may govern the ability of this organism to grow in chill-stored foods. C. botulinum type E spores stored at low temperatures became less germinable with increasing time of storage; this relates to the safety of chill-stored, pasteurized foods. Toxin formation by Aeromonas hydrophila has been quantified at different growth temperatures; this is of relevance to the safety of chill-stored foods. Serotypes of Aeromonas hydrophila most often found in foods have been correlated with isolates from hospitalized patients. This survey is of significance in the spread, infection and control of Aeromonas food poisoning. Tests undertaken using vacuum-packed Bologna-type sausage have shown inhibition of the growth of L. monocytogenes by bacteriocins from lactic acid bacteria.
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