Antimicrobial activity of tigecycline (GAR-936) against Enterococcus faecium and Staphylococcus aureus used alone and in combination.
OBJECTIVE
To evaluate the antimicrobial properties of tigecycline, both alone and in combination with other antibiotics, against multidrug-resistant strains of Enterococcus faecium and Staphylococcus aureus.


METHODS
In vitro study.


METHODS
University laboratory.


RESULTS
Tigecycline, both alone and in combination with other antimicrobial agents, was evaluated against two strains of vancomycin-resistant E. faecium (VREF), three glycopeptide-intermediately resistant S. aureus strains, and one methicillin-resistant S. aureus strain. Tigecycline's activity was compared with that of vancomycin, gentamicin, rifampin, and doxycycline, using time-kill studies and analysis of minimum inhibitory concentrations and minimum bactericidal concentrations. Tigecycline also was evaluated in combination with vancomycin, gentamicin, rifampin, and doxycycline in time-kill studies. The number of log10 colony-forming units/ml at 24 hours was compared among treatment groups and growth control by analysis of variance. All isolates were susceptible to tigecycline, regardless of their susceptibilities to vancomycin or doxycycline. In time-kill studies, tigecycline significantly inhibited the bacterial inoculum of all isolates (p < 0.05). Although none of the tigecycline combinations studied had enhanced killing activity against VREF, when gentamicin was combined with tigecycline, improved effects were found against both strains. Against three of the S. aureus strains tested, the combination of gentamicin and tigecycline demonstrated enhanced or improved activity independently of each strain's susceptibility to gentamicin.


CONCLUSIONS
The multidrug-resistant, gram-positive bacteria tested, including doxycycline-resistant isolates, were susceptible to tigecycline. The combination of tigecycline and gentamicin may have improved or enhanced activity against strains of vancomycin-resistant enterococci and S. aureus.
Mercier
Renee-Claude
RC
College of Pharmacy, University of New Mexico, Albuquerque 87131, USA. rmercier@unm.edu
Kennedy
Christine
C
Meadows
Christina
C
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D024881:Drug Resistance, Bacterial / Q000502:physiology; D004359:Drug Therapy, Combination / Q000494:pharmacology*; D016984:Enterococcus faecium / Q000187:drug effects*; D008826:Microbial Sensitivity Tests / Q000706:statistics & numerical data; D008911:Minocycline / Q000031:analogs & derivatives* / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects*; D000078304:Tigecycline
D000900:Anti-Bacterial Agents; D000078304:Tigecycline; D008911:Minocycline