AISLAMIENTO Y CARACTERIZACIÓN DE CEPAS DE Staphylococcus aureus RESISTENTES A METACILINA (SARM) EN UNA MUESTRA DE QUESO EN EL MERCADO EN PUERTO ESCONDIDO OAXACA, MÉXICO

<p><strong>Background.</strong><em> Staphylococcus aureus</em> is a Gram-positive bacterium that is part of the normal human microbiota but can act as an opportunistic pathogen, causing infections in the skin, soft tissues, and medical devices. Additionally, it is relevant in foodborne diseases (FBD). Dairy products, especially fresh cheese, are common vectors of S. aureus, which can develop antibiotic resistance, complicating its control and treatment. <strong>Objective:</strong> To isolate and characterize methicillin-resistant <em>S. aureus</em> (MRSA) strains in artisanal fresh cheese, evaluating their potential impact on food safety and public health. <strong>Methodology:</strong> Samples of artisanal fresh cheese were obtained from the local market in Puerto Escondido, Oaxaca, Mexico. Microbiological analyses were conducted in the Genetics Laboratory at Universidad del Mar, including Gram staining and hemolysis tests. Methicillin resistance was determined by antibiogram, and resistant strains underwent DNA extraction and amplification by PCR using specific primers. Virulence profiling was conducted via PCR targeting toxin-related genes. The reference strain S. aureus subsp. aureus (ATCC® 43300™) was used as a control. <strong>Results:</strong> A total of 19 <em>S. aureus</em> strains were isolated, 15 of which carried the 23S gene, while five strains exhibited virulence genes such as <em>Clf</em>A, <em>CoA</em>, and <em>NuC</em>. Additionally, enterotoxin genes were identified in seven strains (Enterotoxin E), two strains (Enterotoxin D), and four strains (Exfoliative Toxin etB). These findings confirm the presence of virulent and methicillin-resistant strains in artisanal fresh cheese. The presence of MRSA in dairy products represents a significant risk to public health and food safety. <strong>Implications:</strong> Study limitations include the sample size and the need for further research to assess the prevalence of these strains in other dairy products. <strong>Conclusion:</strong> The study highlights the importance of monitoring and controlling <em>S. aureus</em> in the food chain to prevent zoonotic disease outbreaks and ensure food safety. Molecular characterization of methicillin-resistant strains is crucial for developing effective diagnostic, treatment, and prevention strategies.</p>