Antibiotic susceptibility of coagulase-negative staphylococci (CoNS): emergence of teicoplanin-non-susceptible CoNS strains with inducible resistance to vancomycin

Coagulase-negative staphylococci (CoNS) have become increasingly recognized as important agents of nosocomial infection. One of the characteristics of CoNS is their resistance to multiple antimicrobial agents commonly used for the treatment of staphylococcal infections. CoNS strains (n=745) isolated from a university teaching hospital in China between 2004 and 2009 were tested for antibiotic resistance. The antibiotics were placed into three categories based on resistance levels of the CoNS strains to these antibiotics: high resistance (resistance rate >70%), including penicillin G, oxacillin and erythromycin; medium resistance (resistance rate between 30 and 70%), including tetracycline, clindamycin, ciprofloxacin, trimethoprim/sulfamethoxazole and chloramphenicol; and low resistance (resistance rate <30%), including rifampicin, ceftizoxime and gentamicin. We also found that the prevalence of strains non-susceptible to teicoplanin increased from 4.5 to 6.7% between 2008 and 2009. A one-step vancomycin agar selection experiment and subsequent population analysis revealed potentially vancomycin-resistant subpopulations that have been selected from the teicoplanin-non-susceptible strains. Vigilant surveillance of nosocomial isolates of CoNS is needed to determine their resistance to glycopeptides.