The survival of pathogenic bacteria in, and the microbial spoilage of, salads, containing meat, fish and vegetables

Abstract

An investigation was carried out on the: fate at 9" and 20°C of: (i) two types of non-spore-bearing bacteria, causing food-borne disease, viz. Staphylococcus aureus and Salmonella spp., and two spore-bearing enteropathogens !Clostridiumperfringens and Bacillus cereus) ; and (ii) Lactobacillaceae and yeasts in one type of meat and vegetable salad (pH --4.2, acetic acid content 0.5%) and in one type of shrimp salad (pH == 5.3, acetic acid content 0.3%), preserved at two levels of benzoic acid plus sorbic acid. The pathogens were inoculated at initial densities of 1 04--109/g; for lactic acid bacteria and yeast reliance was placed on naturally occurring organisms.The non-spore-bearing pathogens died out under all conditions, albeit much faster at 20°C. Spore-bearing cells of the Bacillaceae tested remained mostly dormant under the conditions of the tests. Lactobacillacea.e developed fast, also at 9°C and eventually caused souring of the products. Yeasts appeared to play a role at 3°C only. The main antibacterial effect of the salads was demonstrated to be due to its vinegar content and pH.