The antimicrobial activity of cethromycin against Staphylococcus aureus and its relationship with MLST, erm genes and MLSB phenotypes

Abstract Background This study aims to explore the antibacterial activity of cethromycin against Staphylococcus aureus, and its relationship with multilocus sequence typing (MLST), erm genes and macrolide-lincosamide-streptogramin B (MLSB) phenotypes of S. aureus. Results The minimum inhibitory concentrations (MICs) of cethromycin against 245 S. aureus clinical isolates ranged from 0.03125 to ≥ 8mg/L, with the resistance rate of 38.8% in 121 methicillin-resistant S. aureus (MRSA) and 37.1%in 124 methicillin-sensitive S. aureus (MSSA).This study also found that cethromycin had strong antibacterial activity against S. aureus, with the MIC ≤ 0.5 mg/L in 55.4% of MRSA and 60.5% of MSSA, respectively. The main MLSTs of 121 MRSA were ST239 and ST59, and the resistance rate of ST239 isolates to cethromycin was higher than that in ST59 isolates. The top five MLSTs of 124 MSSA were ST7, ST59, ST398, ST88 and ST120, but there was no difference in the resistance of MSSA to cethromycin between these STs. The resistance of ermA isolates to cethromycin was higher than that of ermB or ermC isolates in MRSA, but the resistance of ermB or ermC isolates to cethromycin was higher than that of ermA isolates in MSSA.The resistance of constitutive MLSB (cMLSB) phenotype isolates to cethromycin was higher than that of inducible MLSB (iMLSB) phenotype isolates in MRSA or MSSA. The ermA,ermB and ermC genes was mainly found in ST239, ST59and ST1 isolates in MRSA, respectively. Among the MSSA, the ermC gene was more detected in ST7, ST88 and ST120 isolates, but more ermB genes were detected in ST59 and ST398 isolates. The cMLSB phenotype was more common in ST239 and ST59 isolates of MRSA, and was more frequently detected in ST59, ST398, and ST120 isolates of MSSA. Conclusion Cethromycin had strong antibacterial activity against S. aureus. The resistance of MRSA to cethromycin may had some clonal aggregation in ST239. The resistance rate of S. aureus carrying various erm genes or MLSB phenotypes to cethromycin was different.