Experimental study on the efficacy of combinations of glycopeptides and beta-lactams against Staphylococcus aureus with reduced susceptibility to glycopeptides.
OBJECTIVE
The combination of glycopeptides and beta-lactams has been proposed as an alternative therapy against infections due to Staphylococcus aureus with reduced susceptibility to glycopeptides, though its role is still controversial. Our aim was to evaluate the efficacy (decrease in bacterial concentration after 24 h therapy) of these combinations both in vitro and in vivo.


METHODS
Four strains of S. aureus with different glycopeptide susceptibility (MICs of vancomycin from 1 to 8 mg/L) were used. In vitro experiments were performed by means of time-kill curves while we used the mouse peritonitis model for in vivo evaluation.


RESULTS
Combinations of glycopeptides and beta-lactams showed synergy in in vitro time-kill curves against the four staphylococcal strains, the highest efficacy being detected against the glycopeptide-intermediate S. aureus (GISA) strain (MIC = 8 mg/L) (Deltalog 24 h = -3.19 cfu/mL for vancomycin at 1/2 x MIC and oxacillinat 1/64 x MIC versus -0.56 cfu/mL for vancomycin alone at 1/2 x MIC). On the other hand, no significant increase in efficacy was observed in vivo in the experimental model. The efficacy of the combinations decreased in correlation to the decreasing susceptibility of the strains to glycopeptides, showing only residual activity against the GISA strain (Deltalog 24 h = -1.42 cfu/mL for vancomycin and cloxacillin versus -1.22 cfu/mL for vancomycin).


CONCLUSIONS
In the in vivo setting we were unable to demonstrate the synergism between glycopeptides and beta-lactams observed in vitro; nor did combinations show antagonism against any of the strains. Though the usefulness of these combinations cannot be totally ruled out in highly specific clinical conditions, it seems unlikely that they will provide a serious therapeutic alternative in most hGISA and GISA infections in the coming years.
Domenech
Alejandro
A
Laboratory of Experimental Infection, Infectious Diseases Service, Hospital Universitari de Bellvitge, Universitat de Barcelona, Barcelona, Spain.
Ribes
Sandra
S
Cabellos
Carmen
C
Taberner
Ferran
F
Tubau
Fe
F
Domínguez
M Angeles
MA
Montero
Abelardo
A
Liñares
Josefina
J
Ariza
Javier
J
Gudiol
Francesc
F
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004195:Disease Models, Animal; D024901:Drug Resistance, Multiple, Bacterial; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D006020:Glycopeptides / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008826:Microbial Sensitivity Tests; D010538:Peritonitis / Q000188:drug therapy / Q000382:microbiology; D013203:Staphylococcal Infections / Q000188:drug therapy; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000502:physiology; D013997:Time Factors; D047090:beta-Lactams / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D006020:Glycopeptides; D047090:beta-Lactams