Abstract
Background Staphylococcus aureus can asymptomatically colonize the human anterior nares and skin, and nasal colonization by this bacterium represents a potential risk for development of invasive infections. The aim of this study was to determine the prevalence of S. aureus nasal carriage among healthcare workers and students attending a university hospital and to characterize the isolates phenotypically and molecularly. Methods A cross-sectional study was performed with 324 volunteers. Cultures from nasal samples were obtained and S. aureus isolates were characterized according to their antimicrobial susceptibility profile and four virulence factors-encoding genes. MRSA isolates were characterized regarding their oxacillin/cefoxitin susceptibility, SCCmec, and REP-PCR types. Potential risks for S. aureus and MRSA carriage were analyzed. Results Of 324 nasal samples, 42.9% were identified as S. aureus, of which 28.8% were MRSA. S. aureus carriers were significantly higher in males and students (OR = 2.898, 95%CI 1.553–5.410); however, no variables were associated with MRSA carriage. All isolates were susceptible to vancomycin and the highest rate of resistance was observed for penicillin (90.6%). All isolates harbored the coa gene, and 97.8%, the icaA gene; 15.8% and 6.5% were positive for tst and lukS-PV/lukF-PV genes, respectively. Among MRSA isolates, 45% carried the mecA gene but were phenotypically susceptible to oxacillin/cefoxitin; two harbored the tst and none had lukS-PV/lukF-PV genes. All MRSAs were distributed into six SCCmec types and type I (62.5%) was the most frequent. REP-PCR typing identified four main clusters among MRSA isolates. Conclusion High prevalence of healthcare workers and students were identified as nasal carriers of S. aureus exhibiting different antimicrobial resistance profiles, including mecA-positive oxacillin-susceptible S. aureus (OS-MRSA) and the presence of virulence-encoding genes. Both cohorts may represent potential sources for the emergence of a successful S. aureus strain highly adapted to the hospital environment.
Highlights
Staphylococcus aureus can interact with its host as a commensal member of the microbiota [1] or as an opportunistic pathogen causing a wide range of community and hospitalassociated infections [2,3,4,5,6,7]
A total of 324 volunteers were enrolled in this study, where 103 (31.8%) were healthcare workers, 128 (39.5%) undergraduate, and 93 (28.7%) postgraduate students. e mean age of all participants was 30 ± 11.2 years ranging from 19 to 73 years, where 88 (27.2%) were males and 236 (72.8%) were females
One single nasal sampling was performed on each participant, which does not allow the identification of persistent carriers [33], a high prevalence of S. aureus carriers was detected in this study. e overall prevalence of S. aureus nasal carriage was 42.9% (139/324); among them, 28.8% (40/139) were identified as methicillin-resistant S. aureus (MRSA) carriers; that is, the isolate harbored the mecA gene, representing 12.3% of all participants (Figure 1)
Summary
Staphylococcus aureus can interact with its host as a commensal member of the microbiota [1] or as an opportunistic pathogen causing a wide range of community and hospitalassociated infections [2,3,4,5,6,7]. High rates of colonization by methicillin-resistant S. aureus (MRSA) have been reported among healthcare workers [16, 17], and increasing rates of MRSA colonization among students with continuous hospital exposure have been reported [19]. High prevalence of healthcare workers and students were identified as nasal carriers of S. aureus exhibiting different antimicrobial resistance profiles, including mecA-positive oxacillin-susceptible S. aureus (OS-MRSA) and the presence of virulence-encoding genes. Both cohorts may represent potential sources for the emergence of a successful S. aureus strain highly adapted to the hospital environment
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