Evaluation of molecular mechanisms resistance to macrolide by S. pneumoniae strains isolated from Nemazee and Shahid Faghihi Hospitals in Shiraz

Macrolide Streptococcus pneumoniae is generally mediated by two mechanisms: 23SrRNA methylation and efflux. The aim of this study was to assess the molecular mechanism of resistance in S.pneumoniae strains isolated from intensive care units in Shiraz. This was a cross – sectional study. 50 strains of S.pneumoniae were obtained from the patients admitted to intensive care units (ICU) of Nemazee and Shahid-Faghihi Hospitals, from 2010 to 2011. Suspected colonies were identified by phenotypical and biochemical tests. Organisms were confirmed to be Streptococcus pneumoniae on the basis of the presence of lytA gene by PCR method. Antibiotic resistance was evaluated according to Standard Clinical and Laboratory Standards Institute (CLSI). Macrolide resistance genes were identified by use of ermB and mefA specific primers. Using SPSS software, statistical analysis was performed by means of chi- square test. Resistance to erythromycin, clarithromycin and azithromycin levofloxacin were 18%, 48% and 44% respectively. In this study, 25 strains (50%) had mefA and 21 (42%) had ermB genes. Erythromycin resistance had significant relationships with mefA and ermB genes. The results of our study showed that the predominant mechanism of macrolide resistance was due to mefA gene in this area. Increased macrolide resistance calls for attention to the pattern of resistance in the therapeutic regimens.