Aerobic bacterial, coliform, Escherichia coli and Staphylococcus aureus counts of raw and processed milk from selected smallholder dairy farms of Zimbabwe

A cross sectional study was conducted to enumerate total viable bacteria (TBC), coliforms, Escherichia coli and Staphylococcus aureus in raw (n = 120) and processed (n = 20) milk from individual farms from three smallholder dairy schemes of Zimbabwe between October, 2009 and February, 2010. Data on management factors were collected using a structured questionnaire. A standard pour plate technique was used to enumerate total viable bacteria, while for coliforms, E. coli and S. aureus, counts were assessed by the spread plate technique. The association of total viable bacterial counts and management factors was assessed using univariable and a linear regression model. The log10 TBC for raw milk differed significantly (P < 0.05) amongst the schemes with the lowest (5.6 ± 4.7 log10 cfu/ml) and highest (6.7 ± 5.8 log10 cfu/ml) recorded from Marirangwe and Nharira respectively. The mean log10 of TBC of processed milk (6.6 ± 6.0 log10 cfu/ml) were marginally higher than those of raw milk (6.4 ± 5.6 log10 cfu/ml) but not significant (P > 0.05). The coliform, E. coli and S. aureus counts for raw milk significantly differed (P < 0.05) amongst the study areas. The variation in TBC, coliforms, E. coli and S. aureus counts amongst the schemes could be attributed to differences in milking hygiene where farms with more access to training and monitoring of microbiological quality of milk had lower counts. Linear regression analysis revealed dairy scheme, delivery time and season of milking as independently associated with increased TBC of raw milk. The high TBC of raw and processed milk generally indicated low levels of milking hygienic practices, and high level of post-processing contamination, respectively. The high TBC, coliform, E. coli and S. aureus counts of both raw and processed milk may present a public health hazard. Thus, educating the farmers on general hygienic practices, quickening the delivery of milk to collection centres, or availing cooling facilities on-farm will improve the microbiological quality and safety of milk.

► Viable bacterial counts of raw milk from three smallholder dairies were modelled.
► We investigated factors influencing total bacterial, E. coli and S. aureus counts.
► Season, time taken to cool milk and dairy scheme predicted bacterial counts.
► Use of good pre-and post-milking hygienic practices on farms was recommended.