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

Staphylococcus aureus 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 S. aureus 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, SCCmec typing, and spa-typing allowed the characterization of 1459 strains. S. aureus 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 SCCmec types IV and IVa. The most frequent resistance of S. aureus 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 lukE-D, icaA, sdrC, coa, and gyrA. Sixty-two spa-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 S. aureus surveillance studies.