Microbiological Evaluation and Molecular Discrimination of Milk Samples from Humans and Different Animals

Abstract

Milk is a highly nutritious food and it is important to be free of any pathogenic microbes that could be transmitted to humans and affect public health. A total of 145 milk samples were collected from humans and different animal species (cow, buffalo, ewe, goat, camel, mare, and donkey) and underwent physical examination (color, odor, and taste), chemical analysis for its components (water, total salt, fat, protein, lactose, and ash), and finally microbiological (bacteriological and mycological) examinations. Standard plate count, preliminary incubation count, lab pasteurized count, coliform, Escherichia coli, Staphylococcus species, Salmonella species, yeast, and mold counts were measured. PCR test was performed to differentiate milk from different sources (animals and humans) by producing a specific band for each milk type. The results of the physical examination of different kinds of milk showed different grades of white color with the characteristic odor and taste of each milk type. Chemical examination revealed that the highest water content was in donkey milk and the lowest was in buffalo milk while total solids indicated the highest content in sheep milk and the lowest in donkey milk. The microbiological analysis presented that the standard plate count results were the highest in the milk obtained from sheep and camel, while donkey milk was the least in this regard. Yeast counts were the highest in buffalo milk but cow milk was the highest in mold counts. PCR results of milk types using species-specific primers and DNA template extracted from milk somatic cells revealed a specific band for each milk type as 157, 195, 225, 242, 274, and 711 base pair (bp) for goat, human, sheep, buffalo, cattle milk, and camel milk, respectively. It was concluded that more restrictions must be applied to decrease milk contamination as high microbial counts detected in the present study can affect milk quality, public health, and the dairy industry. PCR used in the current work for milk discrimination used milk somatic cells specifically mitochondrial cytochrome b gene which exhibited high specificity in the PCR reactions and this could be served as a cheap and simple method, compared to other types of PCR.