Survey of nasal colonization by, and assessment of a novel multiplex PCR method for detection of biofilm-forming methicillin-resistant staphylococci in healthy medical students

We surveyed the prevalence of nasal colonization by biofilm-forming methicillin-resistant staphylococci in healthy medical students, who had never had contact with patients, using polymerase chain reaction (PCR) to detect the mec A gene, production of pencillin-binding protein 2′ (PBP2′), and quantitative assay of biofilm formation on polystyrene. Anterior nasal swabs from 90 students were cultured on mannitol salt and oxacillin salt screening agar plates. In total, 231 staphylococcal isolates belonging to 10 species from 88 students were identified, of which 139 from 77 (88%) students were Staphylococcus epidermidis. The overall prevalences of methicillin-resistant and biofilm-forming staphylococci were 48% (43 of 90) and 59% (53 of 90) for the medical students, respectively. In total 30 (33%) students carried biofilm-forming methicillin-resistant staphylococci in the nares, all of which were identified as S. epidermidis. For rapid detection of biofilm-forming methicillin-resistant S. epidermidis (MRSE), we devised a novel multiplex PCR method to assess a total of 243 staphylococcal isolates, including the 231 isolates from the students. The multiplex PCR assay used six primers to amplify atl E and ica ADB, which are responsible for the biofilm formation of S. epidermidis, and mec A genes. The multiplex PCR assay revealed that 68 (96%) isolates were detectable in 71 biofilm-forming MRSE isolates, which corresponded to 93% (28 of 30) of biofilm-forming MRSE carriers. Surveillance of nasal colonization with biofilm-forming MRSE using this multiplex PCR in healthcare workers and patients, might provide useful information for the establishment of infection control procedures toward biofilm-forming MRSE.