[In vitro antibacterial activity of piperacillin-tazobactam combination on hospital isolates and regression curve].

: Minimal inhibitory concentrations (MICs) of piperacillin (P) in combination with 4 micrograms/ml of tazobactam (T) were evaluated by agar dilution for 1,245 strains isolated in 4 hospitals. In addition antibiograms by agar diffusion were performed with disks loaded of 75 micrograms of P + 10 micrograms of T. For naturally non beta-lactamase producing Enterobacteriaceae (E), MIC 50 and 90% of P + T were (microgram/ml): E. coli 1-2; P. mirabilis: 0.5-1; activity was practically identical on plasmid mediated penicillinase (Pase) producing strains. Strains of K. pneumoniae only resistant (R) to amino- and carboxypenicillins (C) had MICs less than or equal to 4 (mode MIC 2); MICs of strains R to cephalothin and/or cefotaxime were 2 to 16 (mode MIC 4). For chromosomal cephalosporinase (Case) producing species, MICs of P + T were less than or equal to 8, including for acquired Pase producing strains, but were greater than or equal to 16 for Case hyperproducing strains. Strains of P. aeruginosa susceptible (S) to C were inhibited by 1 to 16 (with MIC 4) and strains R to C by 8 to greater than 128. MICs were generally 2 to 32 for A. baumannii S to C at 0.12 to greater than 128 for strains R to C. Haemophilus, S or R to ampicillin, were inhibited by 0.008 to 2 (MIC 50 and 90: 0.016-0.12). S. aureus S to methicillin (M), Pase producing on not, were inhibited by 0.5 to 2 (mode MIC 1) and strains R to M by 8 to greater than 128. Activity of P + T for coagulase-Staphylococci was similar.(ABSTRACT TRUNCATED AT 250 WORDS)