Genetic resistance factors and antimicrobial resistance phenotypes in methicillin-resistant Staphylococcus aureus isolates of animals and humans

Objective: To investigate the prevalence, genetic resistance factors, and antimicrobial resistance phenotypes of methicillin-resistant Staphylococcus ( S .) aureus (MRSA) from clinically healthy animals (horses, dogs, and cats) and their human handlers, providing a baseline for broader genes sequencing based on One Health studies to the emergence of resistance as well as guides regarding specific therapies, hospital antibiotic usage/stewardship, and target-specific infection control measures. Methods: This cross-sectional study involved both human and animals. S. aureus isolates derived were characterised for their antimicrobial phenotypes through antimicrobial susceptibility testing with PCR detection of mecA, mecC , and DNA sequencing of mepR, mepA, mepB , and sapep genes for correlation with their antimicrobial resistance phenotypes. Results: Seventy S. aureus isolates from 149 human handlers, 240 horses, and 206 companion animals, including dogs and cats were studied. The prevalence of resistance was highest for penicillins (100.0%) and amoxicillin (94.3%), followed by erythromycin (87.7%), trimethoprim (78.6%), azithromycin (77.1%), imipenem (61.4%), and tetracycline (40.0%). Lower resistance prevalences were observed for ciprofloxacin (27.1%), chloramphenicol (20.0%), trimethoprim-sulfamethoxazole (12.9%), and gentamicin (2.9%). Twenty-six isolates had their DNA sequenced for mepR, mepA, mepB , and sapep genes for correlation with their antimicrobial phenotypes. Transcriptional profiling revealed that both animal and human MRSA isolates exhibited a gene cluster mepRAB (multidrug export protein gene), encoding a MarR-like transcriptional regulator ( mepR ), a M20/ M25/M40 metallo-hydrolase protein gene ( sapep ) encoding resistance to biocides and carbapenems, and a hypothetical protein gene of unknown function ( mepB ). Conclusions: This study demonstrated extensive multidrug resistance in MRSA, revealing similarities in the resistance patterns and multiple antibiotic resistance indices among the isolates. These findings suggest the potential presence of non -mec resistance mechanisms in MRSA, in addition to the mec gene mechanism.