Abstract

Widespread use of Macrolide, lincosamide and Streptogramin B (MLSB) family of antibiotics in the treatment of Staphylococcus aureus (S. aureus) has led to an increased resistance to MLSB antibiotics. The purpose of this study was to determine the frequency of MLSB resistance among clinical isolates of methicillin sensitive S. aureus (MSSA) and Methicillin resistant S. aureus (MRSA) from Mansoura University Children Hospital (MUCH), Egypt, phenotypically by using D‑test and genotypically by detection of erm genes by PCR. Different microbiological samples were collected under complete aseptic condition from patients in MUCH according to the site of infection over a period of 9 months from March 2016 to November 2016. S. aureus isolates were identified using standard microbiological methods. MRSA was detected by growth on oxacillin screen agar plate and cefoxitin disk screen test. Antimicrobial susceptibility of the isolates was determined by Kirby-Bauer disk diffusion method. S. aureus isolates that were found to be erythromycin resistant were further studied for inducible clindamycin resistance using D-zone test according to CLSI recommendations. erm genes in S. aureus isolates were detected by PCR. Among 230 S. aureus isolates, 164 were MSSA (71.3%) and 66 were MRSA (28.7%). Twenty-five MSSA (15.2%), and 37 MRSA (56.1%) isolates were erythromycin resistant. Constitutive MLSB phenotype (cMLSB) (30.3 and 4.2%) and inducible MLSB phenotype (iMLSB) (22.7 and 7.9%) were observed in MRSA and MSSA, respectively by D-zone test. The rate of iMLSB phenotype and cMLSB phenotype in MRSA was significantly higher than in MSSA isolates. The frequency of ermA, ermB and ermC genes were 72.9, 5.4 and 13.5% in MRSA isolates and 60, 4 and 12% in MSSA isolates, respectively. Screening test for of iMLSB‑resistant strains is very important by double disk diffusion test (D‑test). This phenotypic test is simple, accessible and reliable method that can be done in every laboratory and research facility, without the need of costly genetic tests. Since the treatment of patients infected with S. aureus with iMLSB phenotype with clindamycin can lead to the expansion of constitutive resistance (cMLSB) and therapy failure.

Key words: Clindamycin, cMLSB, erm genes, iMLSB phenotype, MRSA, MSSA, S. aureus.