Incidence of pathogenic and indicator bacteria in raw and pasteurized milk in Hawassa city, rift valley of southern Ethiopia

Abstract

A total of 78 raw milk samples from the smallholder dairy producers, 43 from coffee and tea house and catering places and 12 pasteurized milk from kiosks and supermarkets were aseptically collected and tested between January 2009 to August 2010 for bacterial analysis. The milk microbial contaminants considered included: Staphylococcus species, Escherichia coli, Salmonella species, Staphylococcus aureus and Listeria monocytogenes. The prevalence of pathogenic microorganisms tended to increase from point of production to point of distribution and coffee and tea rooms. The overall mean TSC was 3.49, 5.44, 6.72 and 5.63 log10 cfu ml-1 for milk samples collected directly from the udder, from storage containers at farm level and distribution containers upon arrival at selling points and tea room and Catering places, respectively. Mean Staphylococcus species Count (TSC) was significantly different (p<0.05) among the different sample sources within the same farm category except for milk samples collected from tea room and catering places but there was no significant difference in TSC (p<0.05) among the three farm categories for the same sample source. Seventy six percent of the milk samples collected from different sampling points of the three farm sizes and tea room and catering places had >104 cfu ml-1 TSC of milk. Results from the raw whole milk samples collected from different sample sources and pasteurized milk samples, 93% of the 133 milk samples tested were positive for coliform bacteria, while Escherichia coli was detected in 47 (35.34%); Staphylococcus aureus in 54.14%; Listeria monocytogenes in 19.55% and Salmonella species. in 33.08%. This experiment suggested that detection of pathogenic microbes in the collected raw and pasteurized milk samples could be used to improve the keeping quality of milk at different chains of milk production. It was concluded that the detection of the pathogenic microorganisms in the milk samples was an indicator for the presence of potential health hazards for the consumers at different selling points in the milk chain in Hawassa city.