Observational cross-sectional study of nasal staphylococcal species of medical students of diverse geographical origin, prior to healthcare exposure: prevalence of SCC mec , fusC , fusB and the arginine catabolite mobile element (ACME) in the absence of selective antibiotic pressure.

OBJECTIVE: The aim of this study was to investigate co-located nasal Staphylococcus aureus and coagulase-negative staphylococci (CoNS) (mainly Staphylococcus epidermidis ), recovered from healthy medical students in their preclinical year, prior to exposure to the healthcare environment, for the carriage of genes and genetic elements common to both species and that may contribute to S. aureus and methicillin-resistant S. aureus (MRSA) evolution.

DESIGN: Prospective observational cross-sectional study. Carriage of antimicrobial resistance and virulence-associated genes in the absence of significant antibiotic selective pressure was investigated among healthy medical students from geographically diverse origins who were nasally co-colonised with S. aureus and CoNS. Clonal lineages of S. aureus isolates were determined.

SETTING/PARTICIPANTS: Dublin-based international undergraduate medical students.

RESULTS: Nasal S. aureus carriage was identified in 137/444 (30.8%) students of whom nine (6.6%) carried MRSA (ST59-MRSA-IV (6/9), CC1-MRSA-V-SCC fus (3/9)). The genes mecA , fusB , ileS2, qacA / qacC and the arginine catabolic mobile element- arc were detected among colonising nasal staphylococci and had a significantly greater association with CoNS than S. aureus. The rate of co-carriage of any of these genes in S. aureus /CoNS pairs recovered from the same individual was <1%.

CONCLUSIONS: The relatively high prevalence of these genes among CoNS of the healthy human flora in the absence of significant antibiotic selective pressure is of interest. Further research is required to determine what factors are involved and whether these are modifiable to help prevent the emergence and spread of antibiotic resistance among staphylococci.