Plasmid-carried macrolides target site modification erm and efflux msr genes in some Staphylococcus spp. from lower respiratory tract infected patients. Archives of Clinical Microbiology

Abstract

Background: Staphylococcus aureus and coagulase-negative staphylo¬cocci are considered to be among the major causes of nosocomial and community-acquired infections. Macrolides, lincosamides and strepto¬gramin type B (MLS) antibiotics are widely indicated for the treatment of staphylococcal infections. A great concern is the increase in the prevalence of macrolide resistance among Staphylococcus spp. The aim of our study was to detect plasmid-harbored genes responsible for macrolide resistance in staphylococci involved in lower respiratory tract infections (LRIs) in Egypt. Methods and findings: A total of 189 bacterial isolates were recov¬ered from 180 sputum and bronchoalveolar lavage specimens ob¬tained from patients with LRIs. The specimens were collected during the period of 2010 to 2012 from Microbiological diagnostic labora¬tories of two governmental hospitals specialized in the treatment of chest infections, Al-Sadr (Abbassia) and Al-Demerdash hospitals. The antibiogram analysis revealed that 64, out of 189 isolates (33.9%) were resistant to the tested antibiotics (Erythromycin, Clarithromy¬cin, Azithromycin and Clindamycin). Among the resistant isolates, 12 isolates (18.7%) were found to be Gram-positive, including 8 isolates (12.5%) which were identified to be Staphylococcus spp. Among these isolates, four showed constitutive (cMLS) phenotype, while the other isolates exhibited inducible (iMLS) phenotype. The molecular analysis of resistant isolates revealed the presence of plasmids in the eight test isolates. By using PCR, two genes suspected to be responsible for plasmid-mediated resistance could be detected using two specific primer pairs for erythromycin ribosomal methylase (erm) and erythro¬mycin resistance ATP-binding protein (coded as msr). The erm gene was detected in four isolates (50%), while the prevalence of msr gene constituted 25% (detected in two isolates only). Further verification of msr gene was performed by DNA sequencing of the PCR product obtained by using the plasmid extract of one isolate as a template. The nucleotide sequence of msr gene was submitted to the GenBank database, and given the accession code KJ710361. Conclusion: Plasmid-harbored genes (erm and msr) prevail among Staphylococcus isolates involved in LRIs as the 8 resistant isolates of this genus was shown to harbor plasmids, with prevalence of 50% (erm gene) and 25% (msr gene). Therefore, the reasons behind the prevalence of these plasmid-mediated genes among staphylococci have to be studied in order to limit the dissemination of macrolide resistance