Persistent nasal colonization of rare community-acquired methicillin-resistant Staphylococcus aureus clones ST8-IVl (CA-MRSA/J) and ST1930-IVa in healthy adults.

As the increase in infections due to community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA), monitoring of colonization in healthy population is becoming more significant. From nasal cavity of two preclinical medical students who were originally healthy and had neither foreign travel history nor contact with animals, methicillin-resistant S. aureus (MRSA) strains were isolated. For these MRSA, the genotypes, prevalence of virulence factors and antimicrobial resistance determinants were analyzed, along with antimicrobial susceptibility test. These strains were genotyped as (i) ST8-SCCmec-IVl, which was "CA-MRSA/J" clone, known as a unique Panton-Valentine leukocidin (PVL)-negative ST8 MRSA in Japan, and (ii) ST1930-SCCmec-IVa, which belonged to CC96, one of the livestock-associated MRSA, while being a rare type in humans (first detection in Japan). Both strains were susceptible to most antimicrobials, except for oxacillin, and continued to colonize the students for 1 year. These MRSA strains were successfully decolonized by the treatment with nasal ointment of mupirocin, and the eradication of ST8 MRSA strain was confirmed for at least 1 year. The present study revealed the persistent colonization of the rare CA-MRSA clones in healthy adults with unknown route of transmission, suggesting the importance to screen CA-MRSA and its decolonization in healthy individuals.