Ticarcillin: a collaborative in vitro comparison with carbenicillin against over 9,000 clinical bacterial isolates.

The minimal inhibitory concentrations of ticarcillin and carbenicillin were determined for 9,236 clinical bacterial isolates by the broth microdilution method at four participating laboratories. Ticarcillin showed significantly increased activity against Klebsiella pneumoniae (P less than .001), Pseudomonas aeruginosa (P less than .001) and Aeromonas hydrophilia (P less than .005) when compared to carbenicillin, but no signifcant differences were observed against other gram-negative organisms. Ticarcillin was consistently less active against the gram-positive cocci, and these differences were significant for Staphylococcus aureus (P less than .001), Streptococcus agalactiae (P less than .001), Staphylococcus epidermidis (P less than .001) and Streptococcus viridans (P less than .005). Significant regional and institutional differences in susceptibility to the two drugs were observed for several species, including common nosocomial pathogens such as S. aureus, P. aeruginosa, K. pneumoniae and Escherichia coli.