Abstract
Staphylococcus aureus is an important pathogen that can cause Staphylococcal Food Poisoning (SFP). Milk and dairy products are frequently contaminated by this bacterium. In this study, 310 samples (168 bovine raw milk and 142 dairy products) were collected in the Tigray region of Northern Ethiopia, with the objective of detection and enumeration of S. aureus and other Staphylococcus species. Baird-Parker agar for isolation and 16S rRNA gene sequencing for species identification were employed. S. aureus was found in 38.7% of samples with mean count of 4.35 +/- 0.97 log 10 CFU ml -1. The prevalence of S. aureus was significantly greater in raw milk samples (47%) than in dairy products (28.8%). Of all S. aureus positive samples, 34.2% contained >5 log10 CFU ml-1. Samples from cafeterias and restaurants showed the greatest prevalence of S. aureus (P<0.05) compared to other sampling points. Samples from small-scale dairies were twice more likely to be contaminated by S. aureus than traditionally managed dairies (P<0.05, OR=2.0). Coagulase-negative staphylococci (CNS) were found in 51.6% of the samples, with mean count of 6.0±1.21 log10 CFU ml-1. Ten species of CNS were identified and S. epidermidis (36.13%) was the most frequent. The frequency of isolation found in this study indicates that S. aureus and other Staphylococcus spp. may impose public health hazard in dairy products. Therefore, further studies on the enterotoxigenic potential of the isolates, and molecular epidemiology to trace the sources of the contamination are recommended. Key words: Coagulase negative staphylococcus (CNS), dairy products, Ethiopia, Staphylococcus aureus, raw milk.
Highlights
Staphylococcal Food Poisoning (SFP) is among the most prevalent causes of gastroenteritis worldwide
The overall point prevalence of S. aureus in both raw milk and milk products was 38.7% with a mean count of 4.35 ± 0.97 log 10 CFU ml -1
A significant difference (P< 0.05) in the occurrence of S. aureus was observed between raw bulk milk, 47.0%, and milk products, 28.9%, (Table 2)
Summary
Staphylococcal Food Poisoning (SFP) is among the most prevalent causes of gastroenteritis worldwide. In China, a retrospective study (1994 to 2005) revealed that S. aureus was the second most common food-borne agent in homes (Wang et al, 2007). Considering the poor hygiene conditions during production & processing of foods, as well as the shortage of cooling facilities, a high occurrence of SFP is likely. S. aureus grows at a wide temperature range between 6 to 48°C with optimum of 35 to 41°C. It tolerates a pH between 4 to 10 with optimum of 6 to 7, a salt concentration of 0 to 20%, and a water activity (aw ) level of 0.83 to 0.99 with optimum at 0.99 (Cretenet et al, 2011)
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