Diverse Gram-positive bacteria identified from raw and pasteurized cow milk consumed at Gondar town and its environs, Ethiopia

Abstract

Bacterial agents, especially gram-positive bacteria as they are widely distributed in the environment, may contaminate milk all the way from udder of the cow to finished products. This cross-sectional study was carried out from October 2010 to May 2011 on contamination of milk meant for human consumption in Gondar town, Ethiopia. Milk samples were collected from critical control points that were hypothesized to be sources of potential contamination including smallholder milk producers, dairy co-operatives, a milk processing plant, and supermarkets. The hygienic procedures applied during milking, milk collection, transportation, pasteurization, and post pasteurization storage conditions were evaluated. Standard bacteriological cultivation and biochemical assays were used to isolate and identify bacterial species. The results of the current study showed that conditions for contamination of raw milk at different critical points were due to less hygienic practices in udder preparation, sub-optimal hygiene of milk handlers, and poor sanitation practices associated with milking and storage equipment. This was evidenced by the dominant presence of Staphylococcus aureus and Bacillus cereus that can lead to public health hazard due to food poisoning related to enterotoxin production. Out of 140 gram-positive species identified, coagulase positive (32.15%) and coagulase negative (15. 71 %) Staphylococcus species, Rhodococcus equi  (18.57%), Bacillus cereus (12.86%), Nocardia asteroids (5. 71 %) and Micrococcus species (5%) were the most commonly identified pathogens. Generally, 71.43% of the isolates were categorized under cocci while the remaining isolates were rods. In conclusion, this study showed the presence of diverse pathogenic gram-positive bacterial species in raw and pasteurized milk in Gondar town. These results highlighted the need to maintain appropriate sanitary and hygienic measures at each critical point in order to safeguard consumers from food borne pathogens.

Keywords: Bacteria, Critical control points, Hygiene, Milk