Resistance of Xanthomonas maltophilia to antibiotics and the effect of beta-lactamase inhibitors.

We examined the susceptibility of 50 isolates of Xanthomonas maltophilia and the effect of beta-lactamase inhibitors upon the susceptibility. The majority of isolates were resistant to azlocillin, piperacillin, mezlocillin, ticarcillin, cefotaxime, ceftizoxime, ceftriaxone, cefoperazone, and ceftazidime. All isolates were resistant to imipenem, CGP 31608, aztreonam, and carumonam. Although disk susceptibility tests showed that the combination of clavulanate with ticarcillin inhibited many isolates, at a ratio of 1:20 few isolates were susceptible to the combination. Addition of clavulanate to aztreonam and to imipenem failed to make organisms susceptible. Sulbactam combined with cefoperazone made some organisms susceptible, but ampicillin-sulbactam was ineffective, whereas tazobactam combined with piperacillin at a ratio of 1:4 made half the isolates have MICs of 32 micrograms/ml or less. The beta-lactamases from the isolates hydrolyzed all of the beta-lactams.