Afr J Health Sci 2000 Jul-Dec;7(3-4):126-31
Department of Medical Microbiology, School of Medicine, University of Zimbabwe, P. O. Box A178, Avondale, Harare, Zimbabwe.
A study to assess the bacteriological quality of milk and ice cream was conducted using the direct plate count method and the methylene blue dye reduction test. A total of 105 milk and 95 ice cream samples were obtained form two factories (depots) and distributing supermarkets (outlets) in Harare. Under the methylene blue test, all milk and ice cream samples passed the hour and 2 hour tests respectively. However, 99% of the milk and 69% of the ice cream samples reduced the dye after 5.5 and 4 hrs 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 400 cfu / ml and 100 cfu / ml respectively. Organisms isolated in both samples and in all outlets were similar, these included Bacillus spp. Coagulase Staphlococcus spp., microcuccus spp., Steptococcus spp., Diphthroids, Fusiform bacterial Klebsiella spp., and Citrobacter spp. No significant differences were found in the plate counts of the samples obtained from the depots and 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 form strawberry ice cream (0.0096). The study has therefore, revealed that milk and milk product sold in various outlets in Harare contained a variety of bacteria of public health importance and also that the methylene blue dye reduction test is not reliable for the detection of bacterial contaminants in dairy products. It is thus suggested that the use of methylene blue dyes be adapted in combination with other tests such as the plate count in assessing bacterial contaminants in milk products.
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