Bacteriological examination of pasteurized milk and milk products sold in Harare, Zimbabwe

A study was conducted to assess the bacteriological quality of pasteurized milk and ice cream sold in Harare, using the direct plate count method and the methylene blue dye reduction test. Altogether, 105 milk and 95 ice cream samples comprising of 46 vanilla and 49 strawberry flavours obtained from two factories (depots) and 5 distributing supermarkets (outlets). Under the methylene blue reduction test, all milk and ice cream samples passed the 30 min and 2 h tests, respectively. However, 99% of the milk and 69% of the ice cream samples reduced the dye after 5 1/2 and 4 h, respectively. The results from the direct plate counts revealed the presence of both pathogens and non - pathogens. The median plate counts in the milk and ice cream were found to be 400 and 100 cfu/ml, respectively. Organisms isolated in both samples and in all outlets were similar, these included Bacillus spp., coagulase Staphylococcus spp., Micrococcus spp., Streptococcus spp., Diphtheroids, Fusiform bacteria, Klebsiella spp. and Citrobacter spp. No significant differences were found in the plate counts of the samples obtained from the depots and the outlets for the milk (p=0.542, df=1) and ice cream samples (p=0.377, df=1). Results further revealed that there was no significant difference in isolates obtained from milk (p=0.803, df=5) and vanilla ice cream (p=0.279, df=5) using the plate count method. There was, however, significant difference in plate count of isolates obtained from strawberry ice cream (0.0096). The study, revealed that milk and milk products sold in various outlets in Harare may contain variety of bacteria of public health importance and also shown that the methylene blue reduction test is not reliable for the detection of bacterial contaminants in dairy products. The study suggested the use of methylene blue dye in combination with other tests such as the plate count in assessing bacterial contaminants in milk products.