Pathogenic bacteria are transmissible to humans through milk and milk products. Many diseases such as tuberculosis, brucellosis, diphtheria, scarlet fever, Q-fever, and gastroenteritis are transmissible via milk products.
The spoilage of milk products is an enormous economic problem worldwide. The microbial load and incidence of the bacterial pathogens in foods are indicators of food quality. Many of the microbiological hazards associated with dairy products such as butter, cheese, and yoghurt are derived from the raw milk.
Farm animals represent a major reservoir of pathogens that can be transferred to milk. Staphylococcus aureus, Salmonella spp., Listeria monocytogenes, Escherichia coli O157:H7 and Campylobacter are the most frequent potential pathogens associated with milk or dairy products in industrialized countries.
Raw milk provides a potential growth medium for the development of bacteria that can be controlled or destroyed through the pasteurization process.
Surface taints of butter may develop as a result of growth of Flavobacterium spp., Pseudomonas putrefaciens, and Shewanella putrefaciens. The fruity odours, rancidity, and proteolytic activity may be caused by the growth of Pseudomonas fragi and occasionally, Pseudomonas fluorescens.
During the production of hard cheeses, some bacteria such as L. monocytogenes, S. aureus, and Salmonella can survive without subsequent growth.
The potential threat of pathogenic bacteria has been minimized and the numbers of outbreaks involving milk and milk products have steadily declined mainly due to modern milk production practices which emphasize sanitary measures, improved udder health, herd inspections, proper cooling, careful handling and storage of raw milk, and almost universal use of pasteurization.
Common microorganisms in milk and milk products
