Susceptibility of ticarcillin-resistant gram-negative bacilli to different combinations of ticarcillin and clavulanic...

The susceptibility of ticarcillin-resistant and of ticarcillin-susceptible Gram-negative bacilli to different combinations of ticarcillin and clavulanic acid has been investigated. Susceptibility to ticarcillin has been restored in ticarcillin-resistant isolates in proportion to the amount of clavulanic acid in the combination and depending upon the species. The decrease in the MICs of ticarcillin was excellent to good in Proteus, Morganella, Providencia, Escherichia coli and Klebsiella, moderate in Enterobacter, Citrobacter and Serratia, but poor in Pseudomonas aeruginosa. An unfavourable effect of clavulanic acid on the MICs of ticarcillin was observed in some isolates belonging to species with inducible beta-lactamases.