ISOLATION OF SALMONELLAE FROM NATURALLY CONTAMINATED DRIED MILK PRODUCTS

Abstract

The number of salmonellae detected in naturally contaminated dried milk products, especially some time after manufacture, was generally low. These organisms apparently were distributed non-uniformly and in different sizes of clumps. Thus, even from a contaminated sample lot, not every 100-g portion would show the presence of salmonellae. Reconstitution (wet blending) of a larger amount of sample and then testing the equivalent of 100 g of solids increased the chances of Salmonella detection. Reconstitution conditions in the pre-enrichment step appeared important to obtain a higher recovery of salmonellae from contaminated dried products. Reconstitution of the samples initially in a lesser volume of medium to produce a high osmotic environment, rehydration incubation for some time (e.g. 1 hr) and then dilution to 1:10 solid to liquid ratio before pre-enrichment incubation seemed to be beneficial. A non-selective pre-enrichment medium, such as lactose broth, also produced recoveries higher than brilliant green water. Rehydration at high temperature (e.g. 45 C) appeared influential. However, because of low levels of salmonellae present in the test samples and relatively few number of samples used for the tests, some of the pre-enrichment conditions were not shown to have a statistically significant influence on recovery of salmonellae.