The prevalence and antimicrobial susceptibility profiles of Staphylococcus aureus and non-aureus staphylococci isolates from dairy cows in Rwanda

Authors: Innocent Rwamuhizi, Felicien Shumbusho, James Hanks, Janvier Nsabimana, Vestine Musanayire, Vestine Uwitugabiye, Florien Nkurunziza, and Charles Ruhimbana

Arch.Life.Sci.Res. 2026. vol. 2, Iss. 1 pp:17-24
Doi: https://doi.org/10.51585/alsr.2026.1.0010

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Abstract:

The transmission of zoonotic pathogens, including antimicrobial-resistant Staphylococcus aureus and non-aureus staphylococci (NAS), represents a significant public health concern. Contemporary dairy cattle-rearing practices have led to increased antimicrobial use, contributing to the development of antimicrobial resistance. This study aimed to determine the prevalence and antimicrobial susceptibility profiles of S. aureus and NAS isolated from dairy cattle in Rwanda. A cross-sectional survey was conducted on 94 dairy farms across four provinces. Of 1,941 milk samples screened using the California Mastitis Test (CMT), 308 CMT-positive samples underwent further bacteriological analysis. Mastitis prevalence was statistically significantly associated with location, lactation stage, and bacterial species, but not with breed or parity. Bacterial culture and biochemical methods were employed to identify S. aureus, NAS, and other environmental bacteria. Antimicrobial susceptibility testing (AST) was performed using the Kirby–Bauer disk diffusion method with commonly used veterinary drugs. The most prevalent bacterial isolates were NAS (62.7%), followed by S. aureus (16.2%) and other environmental bacteria (21.1%). AST results indicated that S. aureus and NAS exhibited high resistance to penicillin (90% and 73.6%, respectively), streptomycin (38% and 52.3%), and tetracycline (40% and 41.97%), but high sensitivity to cefotaxime (4.00% and 2.07%), amoxicillin-clavulanic acid (10.0% and 6.74%), and gentamicin (0% and 3.11%). Multi-drug resistance (MDR) was observed in NAS (30.0%), S. aureus (32.64%), and other bacteria (13.84%). Further research is required to identify antimicrobial resistance (AMR) genes and genotypes at the molecular level in NAS and S. aureus isolates.

Keywords:

Antimicrobial resistance, S. aureus, NAS, Dairy cows, Mastitis, Rwanda

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