STENOTROPHOMONAS (XANTHOMONAS) MALTOPHILIA - IN-VITRO SUSCEPTIBILITY TO SELECTED ANTIMICROBIAL DRUGS, SINGLE AND COMBINED, WITH AND WITHOUTDEFIBRINATED HUMAN BLOOD

Sixteen selected isolates of Stenotrophomonas maltophilia varied in su sceptibility to the combined phagocytic/serum bactericidal activity of fresh defibrinated human blood (65 vol%). Four representative isolate s (X1, X11, X25, and X50), which differed in susceptibility to cefepim e, ceftazidime, rifampin, and timentin, were subjected to checkerboard microtiter broth dilution tests involving combinations of cefepime pl us timentin, ceftazidime plus ofloxacin, cotrimoxazole plus timentin, rifampin plus polymyxin B, and rifampin plus polymyxin B nonapeptide; all combinations yielded additive or synergistic effects against all f our strains. Unexpectedly, the combination of cefepime plus timentin w as bactericidally active against the two cefepime-resistant isolates. This finding was substantiated by blood/broth plus combined antimicrob ial drug assays. Cefepime plus timentin effectively killed all four te st strains. Ofloxacin combined with ceftazidime was bactericidally act ive against the test strains, including two isolates (X11, X50) with i ntermediate ofloxacin sensitivity. Cotrimoxazole plus timentin in bloo d, but not in broth, was bactericidal for the timentin-resistant isola te X25. As expected, various triple combinations of chemotherapeutic a gents in blood and broth revealed polymyxin B plus rifampin, regardles s of the third combination partner, to exert bactericidal activity aga inst all test strains. Similarly, rifampin combined with ofloxacin and ceftazidime was bactericidally active in blood and broth. The observa tion that timentin combined with cefepime was effective against cefepi me-resistant strains of S. maltophilia might prove of clinical relevan ce with regard to chemotherapy of nosocomial infections due to multipl e-antibiotic resistant strains of this opportunistic pathogen.