Biofilm formation in erythromycin-resistant Staphylococcus aureus and the relationship with antimicrobial susceptibility and molecular characteristics

Abstract Purpose In this study, we aimed to investigate biofilm formation characteristics in clinical Staphylococcus aureus ( S. aureus ) isolates with erythromycin (ERY) resistance from China and further analyze their correlations with antimicrobial susceptibility and molecular characteristics. Methodology A total of 276 clinical isolates of ERY-resistant S. aureus , including 142 methicillin-resistant S. aureus (MRSA) strains and 134 methicillin-susceptible S. aureus (MSSA) strains, were retrospectively collected in China. Biofilms were determined by crystal violet staining and ERY resistance genes ( ermA , ermB and ermC ) were detected by polymerase chain reaction. Inducible clindamycin resistance was examined by D test and multilocus sequence typing, and clonal complexes (CCs) based on housekeeping genes were further determined. Results The frequency of biofilm formation among ERY-resistant S. aureus was 40.9% (113/276) in total and no significant difference was found for the frequency of biofilm formation between ERY-resistant MRSA and ERY-resistant MSSA (44.4% vs 37.3%, P  > 0.05). In ERY-resistant MRSA isolates, the frequency of biofilm formation in ermA -positive, gentamicin-resistant and ciprofloxacin-resistant isolates was higher than that in ermA -negative, gentamicin-sensitive and ciprofloxacin-sensitive isolates, respectively (63.9% vs 23.6%, P P P S. aureus isolates with ERY resistance was significantly higher compared with that in CC59 S. aureus (both P Conclusion The ermA gene, and gentamicin, ciprofloxacin and tetracycline resistance facilitate biofilm formation in ERY-resistant MRSA isolates and, moreover , ERY-resistant S. aureus isolates with positive biofilm formation exhibited clonality clustering regarding CC239 and CC7.