Abstract:
Increased resistance of Staphylococcus aureus isolates to existing antimicrobials constitutes
a major concern in human and veterinary medicine. This study aimed at determining the
prevalence, antimicrobial susceptibility pro les, and molecular characteristics of S. aureus
from raw bovine milk in dairy and pastoral farms in Morogoro urban and Mvomero districts,
Tanzania. In a cross-sectional study, 397 raw bovine milk samples were collected and carried to
the laboratory. Conventional Gram staining, colony morphology on blood agar, and mannitol
salt agar, along with biochemical tests, were used for S. aureus identi cation. Antimicrobial
susceptibility testing (AST) was performed using the disk di usion method, while multiplex
polymerase chain reaction (PCR) was used to detect virulence and antimicrobial resistance
genes. Data were analyzed using Epi Info (Version 7). Out of the 397 samples, S. aureus was
con rmed in 124 (31.2%). Contamination of raw bovine milk by S. aureus in the study area was
associated with poor milking hygienic measures. The AST revealed that all S. aureus isolates
were susceptible to chloramphenicol and cefoxitin, while the highest resistance 116/124 (93.5%)
was noticed for penicillin. Resistance to other antimicrobials varied between 1.6-28.2%. Of
the 124 S. aureus isolates, 80 (64.5%) possessed spa gene, with 76/80(95.0%) harboring more
than seven tandem repeats. One of the S. aureus isolates, 1/124 (0.8%), harbored a mecA
resistance gene. The presence of antimicrobial-resistant S. aureus isolates in raw bovine milk
at the farm level is alarming and requires herd health improvement interventions to protect
society.
