molecular epidemiology, virulence factors, antibiotic resistance and risk factors for nasal carriage of <i>staphylococcus aureus</i> in a teenage student population: high prevalence of oxacillin susceptible mrsa isolates

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 methicillinresistant 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 mecapositive s. aureus strains, including 6.07% oxacillin-resistantmrsa(or-mrsa)and11.56% oxacillin-susceptiblemrsa(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 ormrsa, and os-mrsa isolates, respectively. the most common spa types were t11332 (14.3%) and t012 (11.4%) in os-mrsa isolates. ericpcr 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 mdrca-mrsa nasal carriage among iranian healthy school children community.