Synergistic Effects of Vsncomycin, Penicillin, and Gentamicin against Vancomycin-Resistant Enterococci

Abstract

Background : Because of the resistance that enterococci aiready exhibit to a variety of

antimicrobial agents, the emergence of vancomycin resistance is troublesome. The

combined regimes may offer a treatment for patients infected with vancomycin-resistant

enterooocci. We examined the antibiotic synergistic killing of clinical isolates of

vancomycih-resistant enterococci belonging to genotypic resistance classes A, B, and C.

Methods : Nine strains of vancomycin-resistant enterococci and 2 strains of

vancomycin-susceptible enterococci were utilized in this study. MICs were determined

by agar dilution method. Synergistic inhibition of growth was assessed by addition

vancomycin(8㎍/mL), penicillin(2㎍/mL), gentamicin(1㎍/mL), or combinations of these

antibiotics to cultures in the early logarlthaic phase of growth. Synergy was defined as

a decrease in CFU/mL by at least 2 log10 after 24 h compared with the effect of the

most active single agent.

Results : Vancomycin-penicillin-gentamicini and vancomycin-penicillin resulted in 2 or

more logs of killing above that the most effective single agent for all VanA and VanB

strains. All VanC strains were resistant to any antibiotics combination.

Conclusion : Triple combination therapy arid vancomycin plus penicillin regimen may

be effective for the treatment of infections caused by vancomycin-resistant enterococci

belonging to genotypic classes VanA and VanB. Further studios are needed for the new

therapeutic regimen agaist VanC strains.