Fate of Listeria monocytogenes and members of the Enterobacteriaceae group along the processing line of 'Wara' a Southwestern Nigeria soft cheese.

This study aimed at evaluating the survivability of Listeria monocytogenes and members of the Enterobacteriaceae group of organisms during the processing and storage of wara, a southwestern Nigerian un-ripened soft cheese. Pasteurized milk inoculated with L. monocytogenes at 10(1) or 10(2) CFU/ml was used to process the cheese. Samples were taken along the processing steps and throughout a five-day storage period at 15 and 28 degrees C for populations of L. monocytogenes and Enterobacteriaceae. On the fourth storage day, portions of the control cheese (not inoculated with L. monocytogenes) were fried in vegetable oil, mimicking the practice of southwestern Nigerian cheese processors. The results indicated that L. monocytogenes, at both inoculation levels, did not survive the processing of wara. In samples initially inoculated with 10(1) CFU/ml of L. monocytogenes, the Enterobacteriaceae counts increased from 3.35-3.48 Log10 CFU/g on the first day of storage to 7.63-8.46 Log10 CFU/g at 28 degrees C and 5.41-6.34 Log10 CFU/g at 15 degrees C after storage for 5 days. The populations of the Enterobacteriaceae group increased with the extension of storage time in the contaminated, as well as the control cheeses. Overall, the survival of Enterobacteriaceae responded to storage temperatures. Frying significantly reduced the populations of Enterobacteriaceae. The study suggests that wara can serve as a vehicle to transmit illness if its microbial quality is not appropriately managed.