Nasal Colonization of Serine Protease esp-Positive Staphylococcus epidermidis Affecting Staphylococcus aureus

Background: Staphylococcus aureus is a common colonizer of the nasal vestibule found in approximately 20%–30% of healthy adults, while Staphylococcus epidermidis appears to be the most frequent colonizer in all regions of the upper respiratory tract. Esp, a serine protease of S. epidermidis, was reported to inhibit S. aureus colonization. This study was performed to examine the nasal colonization of S. aureus and S.epidermidis and the presence of esp determinants. Methods: Nasal swab specimens from 54 patients were cultured on blood agar plates (BAP) and selective media for S. aureus for bacteria isolation. After 48 hours of incubation with BAP, three or four colonies suspected of being coagulase-negative staphylococci (CNS) were identified by mass spectrometry. Polymerase chain reaction (PCR) for esp was performed on all CNS isolates identified as S. epidermidis. Results: Forty-three S.epidermidis strains were isolated from 18 (33.3%) of the 54 patients.Nine (50.0%) of the 18 patients carried S. aureus, while the other nine did not. Of the 36 S. epidermidis non-carriers, 13 (36.1%) were colonized by S. aureus. All S. epidermidis strains were confirmed by PCR to have esp determinants. Conclusion: S. epidermidis colonization did not affect S. aureus colonization in the nasal cavity. All S.epidermidis strains harbored the esp gene. There were no differences in the nasal colonization rates of S. aureus according to the presence of esp-positive S. epidermidis. Further research on the characterization of S.epidermidis in Korea is needed to understand the association between S. epidermidis and S. aureus colonization.