Mk. Hayden et al., BACTERICIDAL ACTIVITIES OF ANTIBIOTICS AGAINST VANCOMYCIN-RESISTANT ENTEROCOCCUS-FAECIUM BLOOD ISOLATES AND SYNERGISTIC ACTIVITIES OF COMBINATIONS, Antimicrobial agents and chemotherapy, 38(6), 1994, pp. 1225-1229
The effects of teicoplanin (8 mu g/ml), ampicillin (64 mu g/ml), imipe
nem (32 mu g/ml), and gentamicin (4 mu g/ml), alone and in combination
, against 13 unique blood isolates of vancomycin-resistant (MIC for 90
% of isolates tested [MIC(90)], 512 mu g/ml), teicoplanin-susceptible
(MIC(90), 2.0 mu g/ml), ampicillin-resistant (MIC(90), 128 mu g/ml), a
nd non-beta-lactamase-producing Enterococcus faecium (vancomycin-resis
tant enterococci [VRE] isolates) were evaluated by time-kill studies.
All 13 isolates exhibited high-level resistance to streptomycin; 7 iso
lates exhibited high-level gentamicin resistance (HLGR). After 24 h of
incubation, ampicillin (64 mu g/ml) combined with gentamicin (4 mu g/
ml) was bactericidal against three of the VRE isolates that did not di
splay HLGR. Synergy between ampicillin and gentamicin was not observed
against these isolates. Teicoplanin (8 mu g/ml) alone was bactericida
l at 24 h against five of six VRE isolates that lacked HLGR, but was n
ot bactericidal against any HLGR VRE isolate at that time point. The a
ddition of ampicillin (64 mu g/ml) or imipenem (32 mu g/ml) to teicopl
anin did not significantly enhance the killing of HLGR VRE isolates as
a group (P = 0.335). However, there was a trend toward improved killi
ng of some HLGR VRE isolates by teicoplanin plus imipenem. Vancomycin
(32 mu g/ml) combined with ampicillin (64 mu g/ml) was neither bacteri
cidal nor synergistic against HLGR VRE isolates. Overall, bactericidal
activity was attainable against 7 of 13 VRE isolates at 24 h.