Evaluation of Microbial Contamination of Selected Pasteurized Milk Products Available for Sale at Food Outlets in Karapitiya, Galle, Sri Lanka

Abstract

Background: Milk plays a significant role in the diet, and it is an excellent medium for the growth of food-borne pathogens. As the ready-to-drink, pasteurized milk products are expected to be of good quality, regular assessment of these products is necessary to prevent food-borne illnesses. Objective: To assess the prevalence of microbial contamination of selected pasteurized milk products available for sale at food outlets in Karapitiya, Galle, Sri Lanka Methods: A total of 31 pasteurized milk samples of different brands which were 1-2 days prior to their expiry date, were purchased from supermarkets and food outlets in Karapitiya and stored at 2-8°C until laboratory procedures were performed (samples were stored until samples reach to 1-2 days prior to their expiry date). The total plate count and total coliform count of pasteurized milk were obtained by spread plate technique in nutrient agar and MacConkey agar, respectively. The number of counted bacteria was expressed in colony-forming units per mL using the formula. The presence of milk-borne pathogens was determined by using standard biochemical tests, catalase, coagulase and KIA etc. Results: Total plate count and total coliform count of pasteurized milk were compared with the standard plate count limits (20 000 SPC/mL) and total coliform count limits (10 CFU/mL). In this study, out of 31 milk samples, 10 (32.3%) exceeded the standard plate count limit and 15 samples (48.4%) exceeded the coliform count limit. Overall, 20 samples (64.5%) showed bacterial contamination. Staphylococcus aureus, Candida species and other gram-negative organisms were isolated in equal proportions (1/31, 3.2%). None of the samples grew Salmonella spp. Coagulase negative Staphylococcus species were isolated in 67.7% (21/31). Conclusions: In this study, the majority of milk samples were beyond the limits of acceptable bacterial counts making them unsatisfactory for consumption. Keywords: Coliform count, Foodborne pathogens, Microbial contamination, Pasteurized milk, Plate count 44