Identification of gram-negative bacteria from critical control points of raw and pasteurized cow milk consumed at Gondar town and its suburbs, Ethiopia

Abstract

Background: Milk is highly prone to contamination and can serve as an efficient vehicle for human transmission of foodborne pathogens, especially gram-negative bacteria, as these are widely distributed in the environment.

Methods: This cross-sectional study of gram-negative staining bacterial contamination of milk meant for human consumption was carried out from October 2010 to May 2011 in Gondar town, Ethiopia. Milk samples were collected from critical control points, from production to consumption, that were hypothesized to be a source of potential contamination. Milk sampling points included smallholder's milk producers, dairy co-operatives, a milk processing plant, and supermarkets. The hygienic procedures applied during milking, milk collection, transportation, pasteurization, and postpasteurization storage conditions at these specified critical control points were evaluated. Standard bacteriological cultivation and biochemical assays were used to isolate and identify bacterial pathogens in the milk samples.

Results: 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 pre-milking udder preparation, sub-optimal hygiene of milk handlers, and poor sanitation practices associated with milking and storage equipments. Among all critical control points considered, transportation containers at milk collection centers and at processing plants were found to be the most heavily contaminated with gram-negative staining bacterial species. Overall, 54 different bacterial species were indentified, and Escherichia coli (29.6%), Pseudomonas aeruginosa (18.5%), and Klebsiella pneumoniae (16.7%), were the most commonly identified gram-negative staining bacterial pathogens. Of particular interest was that no gram-negative staining bacteria were isolated from pasteurized milk samples with varying shelf life.

Conclusion: This study showed the presence of diverse pathogenic gram-negative staining bacterial species in raw milk that may be attributed to the sub-optimal sanitary conditions in the production and processing of milk in the Gondar town region. These results highlighted the need to maintain appropriate sanitary and hygienic measures at each critical point in order to safeguard consumers from foodborne pathogens. Further studies are recommended to identify additional critical control points, and to assess zoonotic risk factors to consumers.