The antimicrobial susceptibility of Stenotrophomonas maltophilia isolates using three different methods and their genetic relatedness.

Stenotrophomonas maltophilia is inherently resistant to many antimicrobials. So far, antimicrobial susceptibility tests for S. maltophilia have not been fully standardized. The purpose of the study was to compare the susceptibility of S. maltophilia isolates against seven different antimicrobials using three different methods and to investigate their genetic relatedness. Although trimethoprim/sulfamethoxazole (SXT) and ciprofloxacin have the lowest MIC values, SXT (98.1%) and ticarcillin/clavulanate (TLc) (73.1%) were found to be the most effective antimicrobials by agar dilution method, which was in accordance with the breakpoints established by NCCLS. Disc diffusion and E-test was in agreement with agar dilution method for SXT. When the isolation dates, clinics, antibiotyping, and AP-PCR data were investigated, two small outbreaks consisting of five and three cases were determined. By using the NCCLS criteria, disc diffusion and E-test were unreliable alternative methods for S. maltophilia, except for SXT. However, the significance of these data should be confirmed by further experimental and clinical studies.