In vitro spectrum of linezolid and other agents against clinical isolates of anaerobes
Abstract number: 902_p788
Linezolid is an oxazolidinone antimicrobial with established in vitro and in vivo activity against aerobic Gram-positive cocci. In infections such as wounds these Gram-positive pathogens may be mixed with other pathogens including anaerobes. The role of linezolid as an anti-anaerobe agent has yet to be determined. This study was performed to establish the in vitro activity of linezolid and comparative agents against recently isolated anaerobes.
Approximately 700 anaerobes were tested for susceptibility to linezolid (LZD), ceftriaxone (AXO), cefoxitin (FOX), clindamycin (CL), and metronidazole (MRD) using twofold dilutions (0.06256 mg/L) of each agent using the NCCLS-recommended broth microdilution method. The sources of test isolates included wounds, abscesses, body fluids, and tissues.
Against all test isolates LZD had an MIC range of 0.06128 mg/L, a mode MIC of 4 mg/L, and MIC50 and MIC90 values of 2 and 4 mg/L, respectively. LZD activity was judged by percentage of isolates inhibited at 2 and 4 mg/L. Overall LZD inhibited 51 and 96% of isolates at 2 and 4 mg/L, respectively; at 2 and 4 mg/L, respectively, LZD inhibited 35 and 95% of Bacteroides fragilis group; 63 and 92% of Clostridium isolates; 71 and 97% of Prevotella isolates; 100% of Fusobacterium isolates; and 100% of Peptostreptococcus isolates. By comparison of MIC90 values LZD was 2- to 64-fold more active than AXO, 0- to 16-fold more active than FOX, and 2- to 32-fold more active than CL against these same groups of isolates. LZD and MRD had virtually equal in vitro activity. Interestingly, all isolates with MICs of 8 mg/L or higher to LZD had MICs of 2 mg/L or less to MRD, while isolates with MICs of 8 mg/L or higher to MRD had MICs of 4 mg/L or less to LZD.
Based on these results and arbitrary use of NCCLS breakpoints for Gram-positive isolates, we conclude that LZD is highly active against anaerobe pathogens, but this needs to be verified by pharmacokinetic and clinical studies."
|Session name:||XXIst ISTH Congress|
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