Molecular characterization of the first community-acquired methicillin-resistant Staphylococcus aureus strains from Central Iran

Abstract

Background: Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) has spread throughout the world with varying regional incidences and different staphylococcal cassette chromosome mec (SCCmec) elements in different genetic backgrounds. No information is available on CA-MRSA in Iran. A cross-sectional study was carried out among healthy students to investigate: (1) the prevalence of CA-MRSA in Central Iran, (2) the molecular epidemiology of such CA-MRSA strains, (3) the antimicrobial resistance patterns of the strains, and (4) the distribution of virulence genes in these CA-MRSA strains.

Methods: A total of 700 nasal swabs were collected and subjected to S. aureus and MRSA-specific isolation procedures. Antimicrobial resistance patterns were determined using the disk diffusion method, and molecular typing was carried out by multi-locus sequence typing (MLST), SCCmec typing, and Staphylococcus protein A (spa) typing for all CA-MRSA isolates. PCR was used to detect various virulence genes.

Results: One hundred fifty-four S. aureus strains were isolated from the anterior nares of 700 healthy students. According to the US Centers for Disease Control and Prevention definitions for CA-MRSA, seven (4.5%) isolates were confirmed as CA-MRSA. CA-MRSA isolates belonged to SCCmec types IV (n = 6) and V (n = 1). The predominant spa-type among the CA-MRSA isolates was t790 (n = 3), with single t660, t084, and t325 isolates; one isolate was not typeable. The predominant sequence type was ST22, t790, SCCmec IV in three isolates, and the four other sequence types were ST25, ST859, ST14, and ST15.

Conclusions: Iranian CA-MRSA strains are genetically diverse with an elevated prevalence of t790/ST22 SCCmec IV isolates. These findings support the need for more effective infection control measures to reduce nasal carriage and prevent dissemination of CA-MRSA in Iran.

Keywords: CA-MRSA; MLST; Virulence-associated genes; spa typing.