Abstract
Purpose : To assess the microbiological quality of some milk products in Abuja, Nigeria capital city; and the resistance of isolates to some broad spectrum antibiotics. Method : Three packs of different brands of yoghurt and pasteurized milk purchased from four different locations were assessed in duplicate. Isolates were identified using growth on agar and broth, Gram’s reaction, colony morphology, biochemical tests results and criteria for disregarding negative cultures. Resistance of isolates from pasteurized milk was determined using the antibiotic sensitivity test (zones of inhibition). Results : 33 bacterial and 12 fungal isolates belonging to 9 and 3 genera respectively were identified from the yoghurt samples. Presence of yeast was found to increase the microbial load of bacterial groups and decrease the load of live and active cultures which was absent in 33% of yoghurt samples. 27% of samples were heat-treated and contained no LAC. A total of 19 bacterial isolates belonging to 6 genera were identified from the pasteurized milk samples. Milk quality based on methylene blue decolourization time measurement revealed that 49% of the assessed samples were of excellent quality, 37% of good quality, 14% of fair quality, and 0% of poor quality. No milk sample was sterile. Among the three antibiotics tested for resistance on the isolated bacterial strains, three different resistance patterns were observed. Conclusion: Our study shows that mesophilic yeast was the main cause of yoghurt spoilage. Sampled yoghurt is unlikely to make a vital input to LAC intake in Nigerian diets and poses some yet undefined risk. Visual inspection of packages, quality assessment of diary plants/vessels and packaging materials, dye reduction tests, refrigeration at all times, and resistance testing should be critically considered before the use of recommended antibiotics.
Highlights
Milk is man’s indispensable food from infancy to old age
Under the standard of identity established by the U.S Food and Drug Administration (FDA), in order for a refrigerated product to be called "yoghurt," it must be produced by culturing permitted dairy ingredients with a bacterial culture, which contains Lactobacillus bulgaricus and Streptococcus thermophilus (Live and Active Cultures, LAC) that convert milk to yoghurt during fermentation[6]
Antibiotic resistance pattern among laboratory bacteria revealed that 33% of isolates (Pseudomonas spp. and Salmonella spp.) were resistant to penicillin. 7% of Pseudomonas spp. isolates were found to be resistant to both penicillin and streptomycin
Summary
Milk is man’s indispensable food from infancy to old age. Pasteurization used since the early 1900s (heating raw milk to 161◦F for 15 minutes) is expected to remove microorganisms from milk[1]. Pasteurized milk may contain microorganisms of special importance to man[3] which its presence or absence in milk products may reflects success or failure of Good Manufacturing Practices (GMP) or cause infection when consumed together with food. This is of economic significance in Africa where the HIV/AIDS and cancer scourge has left the public who consume milk products immunosuppressed and prone to bacterial and fungal infection[4]. The importance of evaluating the aspects of microbial quality of some milk products in Abuja cannot be overemphasized
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