Commensal Staphylococcus isolates from the nasal cavity of community older adults in Valencia (Spain) and their resistance to methicillin and other antibiotics

Methicillin-resistant Staphylococcus aureus strains (MRSA) have been gradually disseminated worldwide, causing nosocomial and community-acquired infections, and healthy carriers of commensal MRSA constitute a reservoir of the pathogen. Other Staphylococcus species (coagulase-negative, CoNS) colonize animals and humans and include also methicillin-resistant strains (MRCoNS). Here we have determined the prevalence of S. aureus and CoNS species in the nasal cavity of community healthy older adults (n= 27, average age: 63.7 years) and their resistance to methicillin and other antibiotics. A total of 35 Staphylococcus isolates were obtained. All individuals (100%) were carriers of at least one Staphylococcus strain; 15% of subjects were S. aureus carriers, and eight subjects (30%) carried two strains. Prevalence of resistance to methicillin was 25% and 35% for S. aureus and CoNS isolates, respectively. Most isolates were resistant to penicillin G (90%) and clarithromycin (45%). Other resistances were less frequent (rifampicin, tetracycline, fosfomycin, ciprofloxacin), and no resistant isolates to chloramphenicol or vancomycin were found. Multiresistant isolates to three or four chemotherapeutic agents were detected (20% of isolates). These results suggest that the nasal cavity of healthy adults may represent an ecological niche for the transfer of resistant determinants between staphylococcal species, and point out that epidemiological surveillance of commensal MRSA carriers should extended also to MRCoNS carriers.