Detection and antimicrobial susceptibility profile of Staphylococcus aureus in Raw and pasteurized milk in and around Haramaya, Ethiopia

Staphylococcus aureus is a zoonotic pathogen responsible for a wide range of clinical diseases in humans and animals, and it plays a major role in foodborne intoxications through contaminated dairy products. Understanding its occurrence and antimicrobial resistance profile in milk is critical for ensuring food safety and public health protection. A cross-sectional study employing a purposive sampling technique was conducted to investigate the contamination rate and antimicrobial resistance patterns of Staphylococcus aureus in bulk-tank, retail, and pasteurized milk collected in and around Haramaya, Ethiopia. Standard bacteriological culture, Gram staining, and biochemical tests were used for identification, while the disc diffusion method was employed to determine antimicrobial susceptibility profiles. Out of 117 milk samples examined, 43 (36.8%) were positive for Staphylococcus aureus. The prevalence was highest in bulk-tank milk (66.7%; 8/12), followed by pasteurized milk (46.7%; 28/60) and retail milk (15.6%; 7/45). The occurrence of Staphylococcus aureus differed significantly between raw (50%; 36/72) and pasteurized (15.6%; 7/45) milk (p ≤ 0.001). Contamination levels ranged from 3.00 ± 0.22 log₁₀ CFU ml⁻¹ in pasteurized milk to 3.85 ± 0.36 log₁₀ CFU ml⁻¹ in bulk-tank milk (p ≤ 0.02). Antimicrobial susceptibility testing revealed high sensitivity to ampicillin (65%), vancomycin (55%), and doxycycline (50%), while notable resistance was observed against penicillin-G (80%), oxacillin (55%), and tetracycline (50%). The high level of Staphylococcus aureus contamination detected in both raw and pasteurized milk underscores potential health risks and inadequate hygiene practices along the milk value chain. Although some isolates were susceptible to ampicillin, emerging resistance to commonly used antimicrobials such as penicillin and oxacillin is concerning. These findings emphasize the urgent need for strict hygienic control during milking, processing, and distribution of milk and routine microbiological surveillance to monitor Staphylococcus aureus contamination and antimicrobial resistance trends. It is also important to implement awareness campaigns on milk safety and antimicrobial resistance prevention. Continuous monitoring and One Health–based interventions are essential to mitigate the spread of resistant Staphylococcus aureus strains through the dairy value chain and safeguard public health.