Antimicrobial Resistance of Staphylococci at Animal Human Interface in Smallholders and Dairy Farms in Central Oromia, Ethiopia

PURPOSE: Staphylococcus species come from a variety of sources and can contaminate milk during milking, cause mastitis and other diseases in animals and humans. The enterotoxins they produce cause food poisoning. Our objectives were to isolate, biochemically characterize, and determine antimicrobial susceptibility profiles of Staphylococcus species from dairy farms in central Oromia, Ethiopia. METHODS: A total of 339 samples (n = 135 [raw milk], n = 135 [udders’ swabs], n = 25 [milkers’ hands swabs], n = 44 [pooled milking utensils’ swabs]) were collected from smallholders and dairy farms. Bacteriological culture and biochemical tests were performed to isolate and identify Staphylococcus species, and the Kirby Bauer disk diffusion method was used for antimicrobial susceptibility testing. RESULTS: Across all sample types and dairy farms, 247 (72.9%) Staphylococcus isolates were obtained which comprised of 101 (74.8%) isolates from raw milk, 98 (72.6%) from udder swabs, 30 (68.2%) from pooled utensil swabs, and 18 (72%) from milkers’ hand swabs. Fifty coagulase-positive Staphylococcus isolates (20 S. aureus, 20 S. hyicus and 10 S. intermedius) subjected to antimicrobial susceptibility tests have shown various degrees of resistance. All S. aureus isolates were 100% resistant to ampicillin and penicillin. Out of 20 S. hyicus isolates, 90% were resistant to ampicillin and 85% to penicillin. S. intermedius isolates (n=10) were 70% resistant to nalidixic acid and penicillin whilst remaining 100% resistant to ampicillin. Five S. aureus, three S. intermedius and two S. hyicus isolates from raw milk, milk utensil swabs and milkers’ hand swabs were multidrug-resistant (resistance to at least three classes of antimicrobials). CONCLUSION: This study revealed a high prevalence of staphylococci in the dairy cattle, milkers and milking utensils with multidrug-resistant coagulase-positive Staphylococcus species suggesting the significance of pasteurization. Further research is encouraged on the factors leading to antibiotic resistance in Staphylococcus species.