ANTIBIOTIC SUSCEPTIBILITY OF STENOTROPHOMONAS (XANTHOMONAS) MALTOPHILIA - COMPARATIVE (NCCLS CRITERIA) EVALUATION OF ANTIMICROBIAL DRUGS WITH THE AGAR DILUTION AND THE AGAR DISK DIFFUSION (BAUER-KIRBY) TESTS

Ninety-six clinical isolates of Stenotrophomonas maltophilia were exam ined with the agar dilution method for susceptibility to 19 antimicrob ial drugs. Doxycycline, cotrimoxazole, timentin, ofloxacin, fosfomycin , and piperacillin + tazobactam, in that order, inhibited the majority of strains. All isolates were resistant to nitrofurantoin. Concurrent disk susceptibility (Bauer-Kirby method) testing, using currently val id NCCLS interpretative criteria for Pseudomonas aeruginosa, uncovered a significant incidence of very major (category I), major (category I I), and minor (categories III and IV) discrepancies for aminoglycoside s, cephalosporins, chloramphenicol, and piperacillin + tazobactam and ticarcillin + clavulanic acid. Therefore, new interpretative criteria indicative of intermediate (I) susceptibility of S. maltophilia to the se various antibiotics were proposed. In addition, new intermediate su sceptibility criteria were proposed for the two beta-lactam-beta-lacta mase inhibitor combinations. It was recommended to exclude ciprofloxac in from test batteries against this microorganism due to the wide scat ter of minimal inhibitory concentration values and diameters of inhibi tion zones; the same was true for polymyxin B. It is hoped that the pr oposed modified, species-specific criteria will improve the clinical u tility of laboratory-generated disk antibiograms with respect to the i nherently multiple antibiotic-resistant, opportunistic pathogen S. mal tophilia.