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

Summary. 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 entero-pathogens ( Clostridium perfringens 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 10⁴-10⁹/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. Lactobacillaceae 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.