Antimicrobial resistance and heat sensitivity of oxacillin-resistant, mecA-positive Staphylococcus spp. from...

Area of Science:

• Microbiology
• Food Safety
• Antimicrobial Resistance

Background:

• Unpasteurized milk can harbor bacteria, including Staphylococcus species.
• The presence of antibiotic resistance genes in foodborne pathogens is a growing public health concern.
• Methicillin resistance in Staphylococcus is often mediated by the mecA gene.

Purpose of the Study:

• To investigate the prevalence of mecA-carrying Staphylococcus species in unpasteurized milk.
• To assess the co-occurrence of other antibiotic resistance genes in these isolates.
• To determine the thermal resistance of mecA-carrying Staphylococcus species compared to Staphylococcus aureus.

Main Methods:

• Isolation and identification of Staphylococcus species from unpasteurized milk samples using oxacillin enrichment.
• Detection of the mecA gene and other antibiotic resistance genes using molecular methods.
• Determination of decimal reduction times (D-values) at 56°C in whole milk.

Main Results:

• Eight mecA-positive Staphylococcus isolates were identified: five Staphylococcus epidermidis, two Staphylococcus lentus, and one Staphylococcus haemolyticus. No mecA-positive Staphylococcus aureus were found.
• All identified mecA-positive isolates carried additional antibiotic resistance genes, indicating potential reservoirs for resistance.
• mecA-Staphylococcus species exhibited significantly lower D-values (1.46–2.82 min) at 56°C compared to Staphylococcus aureus (10.8–20.1 min).

Conclusions:

• Unpasteurized milk contains mecA-carrying coagulase-negative Staphylococcus species that can act as reservoirs for diverse antimicrobial resistance genes.
• Effective heat treatment of milk is crucial for eliminating resistant Staphylococcus species and safeguarding public health.
• Consumption of unpasteurized dairy products poses a risk for the transmission of antimicrobial resistance.