Prevalence of oxacillin-susceptible methicillin-resistant Staphylococcus aureus nasal carriage and their clonal diversity among patients attending public health-care facilities

Context

Nosocomial infections arise from many microorganisms, including Staphylococcus aureus.

Aims

The aim of this study is to determine the molecular epidemiology of circulating methicillin-resistant S. aureus (MRSA) clones among patients attending community and health-care facilities in Nova Friburgo, RJ, Brazil.

Methods

A total of 1002 nasal swab samples were collected from May 2010 to September 2015. S. aureus isolates were identified through phenotypic tests, submitted to antimicrobial susceptibility tests and genotypic analysis to detect mecA, panton-valentine leucocidin (PVL) genes, SCCmec, SPA and multilocus sequencing typing (MLST) typing.

Results

We identified 294 (29.3%) isolates as S. aureus and 91 (9.1%) as MRSA. A total of 17 isolates did not present a correlation between phenotypic and genotypic resistance profiles. Among MRSA isolates, 17 (18.7%) carried PVL genes. A total of 20 different SPA types were determined, being grouped by MLST into eight different sequence types. ST5/t002 was the most prevalent genotype found among these isolates.

Conclusions

There is a gradual colonisation shift happening in the infection pattern by S. aureus in Brazil. The Brazilian Epidemic Clone (ST239-SCCmec IIIa-PVL-) seems to be substituted by isolates from different clonal complexes, such as ST5, ST8 and ST30. The non-correlation between phenotypic/genotypic resistance profile observed in some isolates suggests the presence of other methicillin resistance mechanisms different from mecA presence or a difference in the nucleotide sequence, which prevents the primers to identify the specific region during polymerase chain reaction reactions. MRSA identification should be based on phenotypic and genotypic testing to ensure the various types of resistance mechanisms.