Piperacillin and carbenicillin; a collaborative in vitro comparison against 10,838 clinical bacterial isolates

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The clinical efficacy of carbenicillin for treating serious gram-negative infections caused by Pseudomonas aeruginosa and some members of the Enterobacteriaceae is well established.1, 2 The synergistic effect of carbenicillin and aminoglycosides3, 4 is of significant value in treating infections caused by P. aeruginosa. However, the occurrence of aminoglyco-side- and carbenicillin-resistant strains of Pseudomonas and enteric gram-negative bacilli5–6 indicates the need for other antimicrobics with significant activity against these pathogens.

Piperacillin, formerly known as T-1220, is a synthetic derivative of aminobenzyl penicillin (Fig. 1). In previous reports this antimicrobic has been shown to be much more active than ticarcillin or carbenicillin against most Enterobacteriaceae, P. aeruginosa, Pseudomonas species, Bacteroides fragilis and Streptococcus faecalis.7–13

This study presents an in vitro comparison of carbenicillin and piperacillin against 10,838 clinical isolates of bacteria from four institutions in three widely separated geographic regions.

Materials and methods

Bacterial isolates. T he bacteria tested were consecutive clinical isolates from the laboratories of St. Francis Hospital, Wichita, Kansas; Kaiser Foundation Hospital and St. Vincent Hospital and Medical Center, Portland, Oregon; and The Cleveland Clinic Foundation. A total of 10,838 aerobic and the facultative anaerobic bacterial isolates were tested. The isolates were identified by one of the following: the prepackaged reagent kit AnalyTab Products Inc system, the replicator method,14 and the conventional biochemical and serological methods.15 Four or five quality control strains were tested daily by each institution. The quality control strains included Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923 or 29213), P. aeruginosa (ATCC 27853) and . . .



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