Isolation, Biochemical Characterization, and Antimicrobial Resistance of Staphylococcus aureus Isolated from the Gastrointestinal Tract of Chicken

Abstract

Background: Staphylococcus aureus is a significant zoonotic pathogen with increasing multidrug resistance (MDR), posing serious threats to both veterinary and human healthcare. Poultry products are potential reservoirs, yet limited data exist on gastrointestinal isolates and their resistance profiles in Pakistan. Objective: This study aimed to isolate and biochemically characterize Staphylococcus aureus strains from the gastrointestinal tract of chickens in Abbottabad and evaluate their antimicrobial resistance patterns to commonly used antibiotics, thereby assessing their potential impact on human health. Methods: A descriptive observational study was conducted using four chicken gastrointestinal samples (n = 4) collected from poultry vendors in Abbottabad. Samples were aseptically processed, enriched in Tryptic Soy Broth, and cultured on selective media. Isolates were identified using standard biochemical tests (catalase, coagulase, oxidase, methyl red, motility) and confirmed morphologically. Antimicrobial susceptibility testing was performed using the Kirby-Bauer disk diffusion method against erythromycin, tetracycline, gentamicin, clindamycin, and trimethoprim-sulfamethoxazole. Data were analyzed descriptively using SPSS v27. The study followed ethical standards in accordance with the Declaration of Helsinki. Results: All isolates showed catalase positivity and typical Gram-positive cocci morphology. Coagulase, oxidase, methyl red, and motility tests were negative. Resistance was highest for erythromycin (75%) and tetracycline (50%), with concerning MDR patterns observed, suggesting zoonotic and therapeutic risks. Conclusion: The presence of MDR S. aureus in poultry gastrointestinal tracts underscores their potential as reservoirs for resistant strains transmissible to humans. These findings highlight the need for improved antibiotic stewardship and surveillance in veterinary sectors to safeguard public health.