Prevalence of MLSB Resistance Gene among Clinical Isolates of Staphylococcus aureus in Mashhad, Iran

Background and Aim : Development of drug resistance to Staphylococcus aureus has led to the use of older antibiotics such as macrolide-lincosamide-streptogramin B (MLSB) for the treatment of infections. .The objective of this study is to determine the prevalence of erm and msr genes and the frequency of constitutive MLSB (cMLSB), inducible MLSB(iMLSB) phenotypes using D-test and polymerase chain reaction (PCR) methods.Methods : The present study was done for a period of ۶ months (September ۲۰۱۹- March ۲۰۲۰). During this period a total of ۱۰۰ S. aureus were isolated from different clinical samples such as urine, blood, swabs from different sites etc, by the standard laboratory procedures collected from selected hospitals in Mashhad, Iran. Methicillin resistant Staphylococcus aureus (MRSA) detection was done by using cefoxitin ۳۰μg (BD; USA). Disk induction test was performed to detect the presence of inducible clindamycin resistance among erythromycin resistant S. aureus isolated from clinical samples. Three types of phenotypes were observed by the disk induction test (D-test). After sampling, DNA extraction was performed by simple boiling method and prevalence of erm and msr genes were detected by PCR and electrophoresis.Results : Phenotypic analysis revealed that ۵۲ percent were MRSA and resistance to cefoxitin and ۴۸ percent were methicillin-susceptible S.aureus(MSSA). The result of this study revealed that among ۱۰۰ S. aureus isolates examined, frequency of cMLSB, iMLSB resistant phenotypes were ۳۰, ۱۵ percent respectively and sensitive phenotypes were ۲۹ percent. In addition erm C, erm B and erm A were detected in ۵۲, ۱۳ and ۲۷ percent respectively also msr A and msr B genes were detected ۳۵ and ۸ percent S.aureus isolates.Conclusion : This study demonstrated that cMLSB was the most common phenotype among isolated S. aureus and resistant to erythromycin was mainly due to presence of erm genes.

Keywords:

Staphylococcus aureus , Resistance gene , MRSA