Methicillin-Resistant Staphylococcus aureus (MRSA) in Artisanal Cheeses in México

Area of Science:

• Food Microbiology
• Food Safety
• Public Health

Background:

• Staphylococcal food poisoning is a significant public health concern, often linked to dairy products.
• Raw milk cheeses are potential vehicles for foodborne pathogens.
• Contamination of cheese with Staphylococcus aureus, including antibiotic-resistant strains, requires investigation.

Purpose of the Study:

• To determine the prevalence of Staphylococcus aureus, specifically methicillin-resistant Staphylococcus aureus (MRSA), in raw cow milk cheeses produced in Mexico.
• To identify potential risk factors for contamination, such as cheese type.
• To analyze the characteristics of S. aureus isolates, including enterotoxin A production and biotyping.

Main Methods:

• Screening of 78 unpasteurized cow milk cheese samples for S. aureus.
• Identification of S. aureus using standard microbiological tests (morphology, Gram stain, catalase, coagulase, mannitol salt agar).
• Analysis of methicillin resistance via disk diffusion and Staphylococcus enterotoxin A (SEA) production using dot-blot analysis. Biotyping was also performed.

Main Results:

• 44 out of 78 (56.4%) cheese samples were positive for S. aureus.
• Adobero cheese showed a significantly higher risk of contamination (p=0.002).
• The frequency of MRSA was 18.1% (8/44), and SEA producers were also 18.1% (8/44). MRSA isolates were associated with human ecovar and D biotypes.

Conclusions:

• Raw cow milk cheeses in Mexico can be contaminated with S. aureus, including MRSA and enterotoxin A producers.
• Adobero cheese represents a high-risk product for S. aureus contamination.
• The presence of MRSA in human-associated biotypes highlights potential transmission routes and public health implications.