Antibiotic Resistance Patterns of Methicillin-Resistant Staphylococcus aureus (MRSA) Isolated from Livestock and Associated Farmers in Anuradhapura, Sri Lanka

Introduction: The animal husbandry comes to play an important role according to new economic reforms of the rural economy in South Asia including Sri Lanka, and the rural farming community has a poor knowledge about hygienic issues of animal husbandry, which can lead to spread of pathogenic bacterial strains from animals to humans. Our study was conducted to evaluate methicillin susceptible Staphylococcus aureus (MRSA) colonization and its antimicrobial resistance pattern among livestock (n = 188) and related farmers (n = 94) in Anuradhapura District, Sri Lanka. Methods: S. aureus isolates were identified using mannitol salt agar, coagulase test and DNAase test. The agar plate dilution method was conducted to determine the minimum inhibitory concentration (MIC) of oxacillin against S. aureus. Antimicrobial susceptibility testing for other antibiotics was performed against MRSA isolates using antibiotic containing discs. To assess the MRSA transmission from livestock to humans, we have grouped MRSA strains according to antimicrobial susceptibility patterns against the tested antibiotics. Results: Among MRSA isolates, 14 different groups with similar MIC and antibiotic susceptibility patterns were identified. Of those, 2 groups amongst pigs and pig farmers showed a significant relationship (p = 0.031). The other groups did not show any significant relationship between animals and the farmers. The percentages of MRSA prevalence in pigs and pig farmers were 26.6% each, in poultry and poultry farmers 8.3% and 13.3% respectively, in cattle and cattle farmers 8.3% and 3%. Compared to human MRSA isolates, animal isolates were significantly more resistant to ciprofloxacin (p = 0.031), gentamicin (p = 0.010) and clindamycin (p = 0.011). Similarly, animal methicillin susceptible Staphylococcus aureus (MSSA) isolates were significantly more resistant to ciprofloxacin (p = 0.022) and doxycycline (p = 0.012). Conclusion: Pig farming showed a higher prevalence and 2.4 times higher risk (OR = 2.4, CI95%: 1.2-4.8) of likely transmission of MRSA between animals and humans than cattle and poultry farming. Overall, 65% of MRSA and MSSA animal isolates were multidrug resistant.