National survey of the in vitro spectrum of piperacillin-tazobactam tested against more than 40,000 aerobic clinical isolates from 236 medical centers.

Hospital microbiology laboratories from 41 states participated in a bacterial antimicrobial susceptibility study comparing in vitro results generated by the standardized disk diffusion method. Over 41,000 freshly isolated aerobic and facultative strains, representing all specimen types (except stools and urines), were tested for their susceptibility to piperacillin-tazobactam and 21 other antimicrobial agents. Enterococcus spp. was the second or third most common isolate from intraabdominal, gynecologic, and cutaneous infections, confirming its growing importance as a nosocomial pathogen. Escherichia coli was the most frequent isolate overall, despite the exclusion of urinary tract specimens from the study. Pseudomonas aeruginosa was the second most prevalent species, ranking first in frequency of recovery from lower-respiratory-tract specimens. Piperacillin-tazobactam was the most active beta-lactamase inhibitor combination tested against Gram-negative bacteria. Its activity against Gram-positive bacteria and Haemophilus influenzae was similar to that of ampicillin-sulbactam (95-97% susceptible). Imipenem and piperacillin-tazobactam displayed similar spectrums of activity against Gram-positive organisms and Haemophilus influenzae. Against Enterobacteriaceae, piperacillin-tazobactam and ceftazidime exhibited similarly wide spectrums of activity, but with some gaps, particularly among Enterobacter spp. and Citrobacter freundii. In this large-scale in vitro study, piperacillin-tazobactam and imipenem displayed the widest antimicrobial spectrums, inhibiting > 90% of all isolates tested.