Susceptibility of Haemophilus influenzae to piperacillin-tazobactam combinations: interpretive criteria and quality control limits for standardized tests.
In vitro studies evaluated methods for testing the susceptibility of Haemophilus influenzae to piperacillin-tazobactam combinations. Ampicillin-resistant beta-lactamase-nonproducing strains of H. influenzae may be presumed to be relatively resistant to combinations of piperacillin-tazobactam, even though they frequently appear to be susceptible by disk diffusion methods. Other ampicillin-resistant or -susceptible strains were predictably susceptible; i.e., 130 such strains gave zones of inhibition > or = 26 mm in diameter, and MICs for these strains were < or = 0.125/4.0 micrograms/ml (< or = 1.0/0.12 micrograms/ml when an 8:1 ratio was tested). A resistant category has yet to be defined. For quality control purposes, H. influenzae ATCC 49247 should give zones of inhibition 32 to 38 mm in diameter, and broth microdilution MICs should be 0.12/4.0 to 0.5/4.0 micrograms/ml.
Barry
A L
AL
Clinical Microbiology Institute, Tualatin, Oregon 97062.
Fuchs
P C
PC
Jorgensen
J H
JH
Tenover
F C
FC
Allen
S D
SD
Hardy
D J
DJ
McLaughlin
J C
JC
D000668:Ampicillin Resistance; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D006193:Haemophilus influenzae / Q000187:drug effects*; D008826:Microbial Sensitivity Tests / Q000592:standards*; D010397:Penicillanic Acid / Q000494:pharmacology*; D010878:Piperacillin / Q000494:pharmacology*; D011786:Quality Control; D000078142:Tazobactam; D065093:beta-Lactamase Inhibitors
D004338:Drug Combinations; D065093:beta-Lactamase Inhibitors; D010397:Penicillanic Acid; D000078142:Tazobactam; D010878:Piperacillin