Antimicrobial Susceptibility Profiling of Staphylococcus aureus Isolates from Milk

Aims: This study investigated the occurrence of Staphylococcus aureus in milk and its sensitivity to twenty antibiotics.

Study Design: The research was laboratory-based investigation.

Place and Duration of the Study: The study was carried out at the Laboratory of Hygiene and animal pathology, University of Tiaret, Algeria, between September 2012 and May 2013.

Methodology: Thirty eight milk specimens were collected from cattle and examined to estimate the prevalence of Staphylococcus aureus. The sensitivity of the isolates to twenty (20) antibiotics was evaluated and the presence of methicillin resistant Staphylococcus aureus (MRSA) was also determined.

S. aureus was characterized using standard microbiological methods and confirmation was done using the API Staph Identification System. Antibiotic sensitivity of isolates was evaluated by means of agar diffusion technique while the minimum inhibitory concentration (MIC) was established using broth dilution technique for oxacillin, E-test for tetracyclin, and chloramphenicol respectively.

Results: 55.26% of analyzed samples were contaminated with S. aureus. 100% of Methicillin Sensitive S. aureus were resistant to nalidixic acid, 70% to bacitracin, 65% to spiramycin, and 45% to penicillin and fosfomycin. There was no resistance to vancomycin, chloramphenicol, gentamicin and pristamycin among isolates.

A total of 76% of the isolated strains were found to be resistant to at least 4 antibiotics.

One Methicillin Resistant S. aureus strain (4.76%) was detected and showed multiple drug resistance. This resistance was crossed with all beta lactams and its resistance profile to macrolides was constitutive (MLSB const) while aminoglycosides phenotype was ANT (4’) (4’’).

Conclusion: A high prevalence of S. aureus with multiple drug resistance was established. Improved food safety measures are thus necessary to prevent transmission and spread of antimicrobial resistance by these pathogens.