In vitro combination of tigecycline with other antibiotics in Stenotrophomonas maltophilia isolates

Abstract

Background/aim: The aim of this study was to determine the usefulness of tigecycline in combination treatment of Stenotrophomonasmaltophilia infections by evaluating the in vitro synergistic effects of tigecycline with various antibiotics using the E-test method.Materials and methods: Synergy testing by E-test was performed with various antibiotic combinations in 10 S. maltophilia isolatesidentified as a cause of infection. The antibiotics used in the study included tigecycline (TGC), cefoperazone-sulbactam (CPS),ceftazidime (TZ), levofloxacin (LEV), and trimethoprim-sulfamethoxazole (cotrimoxazole) (TS). Four different combinations (TGCCPS, TGC-TZ, TGC-LEV, TGC-TS) were studied with the E-test synergy method.Results: S. maltophilia isolates were found to have the highest level of susceptibility to trimethoprim-sulfamethoxazole, tigecycline, andlevofloxacin. The fractional inhibitory concentration (FIC) index was calculated as FIC = MICAB/MICA + MICBA/MICB. The FICindex values were calculated and classified as synergistic (FIC 4). According to FIC index values, synergy was found with the highest rate with TGC-CPS and TGC-LEV combinations (20%).Antagonistic activity was not found in any combination.Conclusion: When trimethoprim-sulfamethoxazole cannot be used because of resistance or allergy, tigecycline alone or in combinationmay be included as an alternative option. Although in vitro results are promising, clinical data are required.