INTRODUCTION: Stenotrophomonas maltophilia is an important emerging nosocomial pathogen naturally resistant to carbapenems. Although trimethoprim/sulfamethoxazole (TMP-SMX) is commonly used as a treatment option, resistance to this drug has been recently reported. OBJECTIVE: To evaluate the susceptibility profile of S. maltophilia strains and compare the results obtained by different methods. METHODS: As to susceptibility profile, all strains, which had been routinely isolated at Hospital das Clínicas, São Paulo, in 2007, were evaluated through disk diffusion and microdilution. In accordance with the Clinical and Laboratory Standard Institute (CLSI), TMP-SMX and levofloxacin were tested through both techniques, as well as tigecycline, which was interpreted in conformity with Food and Drug Administration (FDA) regulations. Ticarcillin/clavulanate, ceftazidime, imipenem, meropenem and moxifloxacin were evaluated only through microdilution. The correlation between these methods was assessed by WHONET®. RESULTS: 1.6% of 126 strains were resistant to TMP-SMX, 2.4% to levofloxacin, 23% to ticarcillin/clavulanate, and 54% to ceftazidime. All strains showed minimum inhibitory concentration (MIC) < 2 µg/mL for tigecycline and 96.8% MIC < 2 µg/mL for moxifloxacin. The correlation index between both methods was 100% for TMP-SMX and 89.6% for levofloxacin, respectively. DISCUSSION AND CONCLUSION: Although TMP-SMX is the standard treatment for S. maltophilia infections, there may be resistance to this antibiotic, which hinders the therapeutic approach, hence the significance of susceptibility tests. The disk diffusion technique showed a good correlation with microdilution. Among the new therapeutic options, both tigecycline and moxifloxacin presented significant activity in vitro.
Stenotrophomonas maltophilia; Disk diffusion; Microdilution; Trimethoprim
