Characterization of methicillin‐resistant Staphylococcus aureus strains colonizing the nostrils of Spanish children

Objective To characterize the Staphylococcus aureus strains colonizing healthy Spanish children. Methods Between March and July 2018, 1876 Spanish children younger than 14 years attending primary healthcare centers were recruited from rural and urban areas. Staphylococcus aureus colonization of the anterior nostrils was analyzed. MecA and mecC genes, antibiotic susceptibility, and genotyping according to the spa were determined in all strains, and the following toxins were examined: Panton‐Valentine leucocidin (pvl), toxic shock syndrome toxin (tst), and exfoliative toxins (eta, etb, etd). Multilocus sequence typing (MLST) and staphylococcal cassette chromosome (SCCmec) typing were performed on methicillin‐resistant Staphylococcus aureus (MRSA) strains, as well as pulsed‐field gel electrophoresis (PFGE). Results 619 strains were isolated in 1876 children (33%), and 92% of them were sent for characterization to the Spanish National Centre of Microbiology (n = 572). Twenty (3.5%) of these strains were mecA‐positive. Several spa types were detected among MRSA, being t002 the most frequently observed (30%), associating with SCCmec IVc. Among MSSA, 33% were positive for tst, while only 0.73% were positive for pvl. The 20 MRSA strains were negative for pvl, and 6 (30%) harbored the tst gene. Conclusions methicillin‐resistant Staphylococcus aureus nasal colonization in Spanish children is rare, with t002 being the most observed spa type, associated with SCCmec IVc. None of the MRSA strains produced pvl, but up to 30% of S. aureus strains were positive for tst. This is one of the largest epidemiological studies in which we have screened up to 1876 healthy Spanish children for methicillin‐resistant Staphylococcus aureus (MRSA) colonization. All the isolated strains have been characterized by analyzing their genotype, the presence of mecA and mecC genes, and their antibiotic susceptibility. In addition, Panton‐Valentine leucocidin, toxic shock syndrome toxin, and exfoliative toxins production were analyzed. This epidemiological surveillance study leads to a better understanding of the strain flow and the rate of MRSA nasal carriage among Spanish children, and the prevalence of virulence genes and antimicrobial sensitivities of colonizing strains throughout the country.