Culture-Based Identification and Molecular Confirmation of Vancomycin-resistant Staphylococcus aureus (VRSA) from Porcine Rectal Swabs in Ebonyi State, Nigeria
Veronica Felicitia Nwode
Department of Microbiology, Alex Ekwueme Federal University, Ndufu-Alike, Ikwo, Ebonyi State, Nigeria.
Ikemesit Udeme Peter *
Department of Microbiology, Federal University of Allied Health Science, Enugu State, Nigeria and Department of Public Health, Federal University of Allied Health Science, Enugu State, Nigeria.
Chidinma Stacy Iroha
Department of Pharmacy, Institute of Emerging and Re-emerging Infectious Diseases Research, Alex Ekwueme Federal University Teaching Hospital, Abakaliki, Ebonyi State, Nigeria.
Christiana Inuaesiet Edemekong
Department of Public Health, Federal University of Allied Health Science, Enugu State, Nigeria and Department of Biotechnology, Federal University of Allied Health Science, Enugu State, Nigeria.
Ifeanyichukwu Romanus Iroha
Department of Microbiology, Ebonyi State University, Abakaliki, Ebonyi State, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
Background: Vancomycin-resistant Staphylococcus aureus (VRSA) is a critical public health threat. Its presence in food animals like pigs, a known reservoir for resistant bacteria, poses a severe zoonotic risk, especially in regions with unregulated antibiotic use. This study aimed to isolate and characterize VRSA from pigs in Ebonyi State, Nigeria, focusing on its phenotypic resistance and the presence of the vanA resistance gene.
Methods: A total of 120 porcine rectal swabs were collected from a farm in Ndufe-Alike, Ikwo LGA. Staphylococcus aureus was isolated and identified using standard microbiological methods. Vancomycin resistance was phenotypically screened using the disk diffusion method (10µg vancomycin disk) with an inhibition zone of ≤14 mm indicating resistance. Antibiotic susceptibility testing against a panel of 15 antibiotics was performed for all VRSA isolates. The Multiple Antibiotic Resistance (MAR) index was calculated. Polymerase chain reaction (PCR) was used to detect the vanA gene.
Results: The prevalence of S. aureus was 77.5% (93/120). Phenotypic screening revealed an alarmingly high prevalence of VRSA at 91.67% (66/72) of the tested S. aureus population. These VRSA isolates exhibited extreme multidrug resistance, showing 100% resistance to vancomycin, aztreonam, ceftazidime, imipenem, trimethoprim-sulfamethoxazole, amoxicillin-clavulanate, cefoxitin, and tetracycline. High resistance was also observed to ceftriaxone (91.43%) and streptomycin (88.57%). The isolates remained largely susceptible to gentamicin (97.14%) and levofloxacin (88.57%). The MAR index was 0.87, indicating a high-risk contamination source. Molecular analysis confirmed the presence of the vanA gene in all (n=66) VRSA isolates subjected to PCR.
Conclusion: This study reveals an extraordinarily high prevalence of multidrug-resistant VRSA in swine, all harboring the vanA gene. This indicates a severe reservoir of vancomycin resistance likely driven by intense antimicrobial selection pressure in the farm environment. The findings highlight an urgent public health crisis, necessitating immediate implementation of enhanced antimicrobial stewardship in veterinary practice, rigorous One Health surveillance, and stricter regulations on antibiotic use in Nigerian livestock production.
Keywords: Vancomycin-Resistant Staphylococcus aureus (VRSA), Pigs, vanA gene, multidrug resistance, one health, Nigeria, antimicrobial resistance