Antibiotic Resistance and Molecular Characterization of Staphylococcus aureus Strains Colonizing the Nose and Pharynx

<i>Staphylococcus aureus</i> colonizes the nasal and pharyngeal mucosa of a considerable proportion of the human population, representing a relevant reservoir for the dissemination of antibiotic resistance. This study aimed to determine the prevalence, antibiotic resistance profiles, and molecular characterization of <i>S. aureus</i> strains isolated from the nose and pharynx of healthy individuals of Mexico City, Mexico. Nasal and pharyngeal swabs were taken from 1777 individuals aged between 1 and 99 years. Microbiological identification, antibiotic susceptibility testing, virulence gene detection, SCC<i>mec</i> typing, and <i>spa</i>-typing allowed the characterization of 1459 strains. <i>S. aureus</i> colonization was found in 59.7% of the population, with more of these strains being found in the pharynx than in the nose. MRSA constituted 9.25% of the strains, with a predominance of strains with SCC<i>mec</i> types IV and IVa. The most frequent resistance of <i>S. aureus</i> strains was to penicillin (87.6%), clindamycin (43.4%) and erythromycin (27.2%), with no statistical differences regarding the anatomical sites of isolation. The most frequently found virulence genes were <i>lukE-D</i>, <i>icaA</i>, <i>sdrC</i>, <i>coa</i>, and <i>gyrA</i>. Sixty-two <i>spa</i>-types were identified, and t-189 was the most common. These findings reflect a high colonization rate and genetic diversity, highlighting the importance of considering both anatomical sites in <i>S. aureus</i> surveillance studies.