Antibiotic resistance assessment in S. aureus strains isolated from raw sheep's milk cheese

Area of Science:

• Food microbiology
• Antimicrobial resistance
• Bacterial genetics

Background:

• Raw milk cheeses can be a source of Staphylococcus aureus (SA) contamination.
• Understanding antimicrobial resistance patterns in SA is crucial for food safety.

Purpose of the Study:

• To assess the in vitro antibiotic susceptibility of SA strains isolated from raw sheep's milk cheese.
• To investigate the genetic basis of resistance and the genetic relatedness of these SA strains.

Main Methods:

• Antibiotic susceptibility testing (broth microdilution) against 16 antimicrobials.
• Detection of resistance genes (mecA, ermA, blaZ, vanA-B) and agr typing.
• Pulsed-field gel electrophoresis (PFGE) for strain typing.

Main Results:

• SA strains exhibited resistance to ampicillin (36.1%), penicillin (33.3%), tetracycline (11.1%), and cloxacillin (2.8%).
• High susceptibility (>94.4%) was observed for 12 out of 16 tested antimicrobials, including oxacillin, vancomycin, and erythromycin.
• Absence of mecA, vanA-B, and ermA genes correlated with susceptibility to these key antibiotics. PFGE identified 10 distinct clusters among 32 strains.

Conclusions:

• SA from raw sheep's milk cheese show varied resistance profiles but remain largely susceptible to important antibiotics.
• Genetic analysis confirmed susceptibility and revealed diverse strain populations, highlighting the need for ongoing surveillance.