[Phenotype and Genotype of Staphylococcus aureus Isolated from the Nostrils of Elderly Adults in the Valparaíso Region, Chile, from June 2019 to January 2020].

UNLABELLED: Staphylococcus aureus (S. aureus) persistently colonizes the nares of approximately 20-30% of healthy individuals, and the nasal carriage constitutes a risk of infection and transmission. This pathogen causes mild to severe infections, different strains show variable virulence, and methicillin-resistant S. aureus (MRSA) is a global concern. Due to the worldwide aging of the population, further research in older adults is necessary, such as the study of their microbiota.

AIM: To determine the carriage of S. aureus in older adults in Valparaíso, Chile, and to characterize the phenotype and genotype of their isolates.

METHODOLOGY: In a transversal and descriptive study, S. aureus strains were isolated from nasal swabs of 223 older adults. Antimicrobial susceptibility was determined by agar diffusion technique. The virulence genes: Panton-Valentine leucocidine (pvl), methicillin-resistance (mecA), toxic shock syndrome toxin-1 (tst), and enterotoxin A (sea) were detected by polymerase chain reaction. Genotyping of two methicillin-sensitive S. aureus (MSSA) strains and one MRSA was performed using MiSeq-Illumina and bioinformatics analysis.

RESULTS

We identified 41 S. aureus strains in 18.3% [95%CI: 13.5 - 24.1%] of individuals, and the percentage of S. aureus in men was greater than in women. MRSA was 1.3% [95%CI: 0.3-3.9%] without differences between sexes. The isolates showed high resistance to penicillin, followed by erythromycin, clindamycin, and gentamicin. Twenty-four percent of MSSA strains showed multidrug-resistance. Virulence genes sea (6+/41 strains), mecA (3+/41), pvl (2+/41), and tst (2+/41) were detected. Additionally, the genotypes: ST5-SCCmecI-1B), ST398, and ST45 were identified, showing different virulence.

CONCLUSIONS

Nasal carriage of S. aureus was similar to studies of the general population and the same age group from Latin America and Europe; however, MRSA carriage was higher. Strains from older adults exhibited variable pathogenic potential and antimicrobial susceptibility, identifying the Chilean/Cordobes clone and MSSA strains corresponding to CC398 and CC45 previously described in healthy carriers.