In vitro susceptibility of Stenotrophomonas maltophilia to various antimicrobial combinations

Stenotrophomonas maltophilia has emerged as a significant pathogen in compr omised patients, causing infections which are difficult to treat. Clinical isolates from patients in the Tucson area were tested against single and co mbination antibiotics using three testing methods. Ticarcillin/clavulanate, trimethoprim/sulfamethoxazole and trovafloxacin provided comparable inhibi tory activity, in vitro. Ciprofloxacin, imipenem and ticarcillin were activ e less often. Agreements between disk diffusion and broth microdilution res ults were poor for ciprofloxacin and trimethoprim/sulfamethoxazole; however , agreement was greater than or equal to 90% for the other drugs tested. Ma jor or very major errors were observed with ticarcillin, ticarcillin/clavul anate, and trovafloxacin. The addition of aztreonam to ticarcillin/clavulan ate enhanced the activity compared to ticarcillin/clavulanate alone using t he double-disk diffusion, broth microdilution (checkerboard), and time-kill testing methods. Trovafloxacin exhibited good activity by all three method s, with bactericidal activity at greater than or equal to 2 x MIC. These re sults indicate that the newer fluoroquinolones or the triple combination of ticarcillin/clavulanate plus aztreonam may be potential options for treatm ent of infection caused by S. maltophilia in patients who are intolerant to or fail trimethoprim/sulfamethoxazole therapy. (C) 2001 Elsevier Science I nc. All rights reserved.