Zoonotic Potential of Staphylococcus aureus Associated with Goat, Antibiotic Resistance and Virulence Factors

Staphylococcus aureus is an important zoonotic bacterial pathogen associated with a wide range of infections in animals and humans, and small ruminants may act as significant reservoirs for antimicrobial resistant strains. The present study investigated the occurrence, phenotypic characteristics, antimicrobial resistance patterns, and zoonotic potential of Staphylococcus aureus isolated from goats in major livestock producing districts of Punjab, Pakistan. A field based cross sectional survey was conducted during 2022-2023, and a total of 268 samples were collected from both healthy and diseased goats, including milk (n = 56), nasal swabs (n = 174), and skin/wound swabs (n = 38). Samples were processed using standard bacteriological methods. Isolation was performed through selective enrichment followed by plating on Mannitol Salt Agar, and phenotypic identification was carried out using colony morphology, Gram staining, catalase, coagulase, and hemolysis tests. Antimicrobial susceptibility testing was conducted using the disc diffusion method against commonly used antibiotics, including penicillin, oxacillin, tetracycline, erythromycin, gentamicin, ciprofloxacin, and vancomycin, following locally adopted testing standards. Phenotypic methicillin resistant S. aureus (MRSA) was identified using oxacillin resistance. Out of the 268 samples, 98 (36.6%) were positive for S. aureus. The highest rate was in skin/wound swabs (47.4%) and followed by nasal swabs (35.6%) and milk (32.1%). A district-wise difference was noted with the prevalence varying between 30.8% to 40.0%. A majority of the isolates were β-hemolytic (57.1%), which is related to higher virulence. Testing for antimicrobial susceptibility demonstrated a high resistance to penicillin (79.6%) and tetracycline (46.9%), vancomycin presented the better activity (93.9% susceptibility). Phenotypic MRSA made up 34.7% of all isolates, and 49.0% were considered multidrug resistant. Although our results reveal that it is highly prevalent in goats, it poses a significant risk of zoonotic transmission to those who handle livestock. Phenotypic surveillance at the strain level and prudent use of antimicrobials are necessary to control public health hazards in a One Health perspective.