Molecular Epidemiology, Virulence Factors, Antibiotic Resistance and Risk Factors for Nasal Carriage of Staphylococcus aureus in A Teenage Student Population: High Prevalence of Oxacillin Susceptible MRSA Isolates

Abstract

Background: Asymptomatic carriage of Staphylococcus aureus can lead to endogenous infections and cross-transmission to other individuals. Objectives: The prevalence, molecular epidemiology, antibiotic resistance, and risk factors for nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) were studied in school children in Ardabil, Iran. Methods: Totally, 510 nasal samples were collected during 2017. Isolates were identified and subjected to antimicrobial susceptibility testing, identification of oxacillin resistance, and molecular typing. Results: Totally, 13.5% of volunteers were positive for methicillin-susceptible Staphylococcus aureus (MSSA) and 17.5% colonized with mecA positive S. aureus strains, including 6.07% oxacillin-resistant MRSA (OR-MRSA) and 11.56% oxacillin-susceptible MRSA (OS-MRSA). Excluding β-lactam antibiotics, high resistance rate was observed for erythromycin (71%), tetracycline (25.8%), clindamycin (35%) in our isolates. Surprisingly, 11% of the isolates [OR-MRSA (25.8%), OS-MRSA (10.1%), and MSSA (5.7%) isolates] were resistant to mupirocin. Moreover, 18 (58%), 29 (49%), and 29 (42%) of OR-MRSA, OS-MRSA, and MSSA isolates were multidrug-resistant (MDR), respectively. Overall, 97.48% of isolates carried ≥ 3 toxin encoding genes. The pvl gene was found in 46 (29%) isolates. In comparison, 25.50% of MRSA (9.60% OR-MRSA and 34% OS-MRSA) and 33% of MSSA isolates carried pvl gene. SCCmec type IV had the highest rate among OR-MRSA (87%) and OS-MRSA (74.5%) isolates, which indicates CA-MRSA phenotype. Eleven and 21 spa types were identified in OR-MRSA, and OS-MRSA isolates, respectively. The most common spa types were t11332 (14.3%) and t012 (11.4%) in OS-MRSA isolates. ERIC-PCR revealed high genetic diversity among isolates. The number of students in classroom and incomplete antibiotic course were associated with OS-MRSA nasal carriage. Conclusions: This study showed a high proportion of MDR CA-MRSA nasal carriage among Iranian healthy school children community.