Stenotrophomonas maltophilia: Antimikrobik Duyarlılık Testi Sonuçları ve Seftazidimin Moksifloksasinle Kombinasyonunun In Vitro Etkinliği.

Objective: Recommended combination for the treatment of serious Stenotrophomonas maltophilia infections is ticarcillinclavulanate and co-trimoxazole (SXT). However, first agent is not available in our country, and the second component may be a matter of antimicrobial resistance or intolerance. Therefore, we aimed to evaluate antimicrobial susceptibility testing results of S. maltophilia and in vitro activity of ceftazidime and moxifloxacin as a potential therapeutic alternative. Methods: S. maltophilia strains isolated from clinical samples in Infectious Diseases and Clinical Microbiology Laboratory between 1 October 2007-23 November 2017 were included in the study. Disk diffusion antimicrobial susceptibility test results of the strains were evaluated retrospectively. The in vitro activity of combination of ceftazidime and moxifloxacin against 24 of these strains was investigated by Etest®. Results: During the study period, 649 S. maltophilia strains were isolated from 649 different patients, and 94%, 93%, 92%, 81%, 60%, 55%, 45%, 41%, 38% of the strains were susceptible to tigecycline, moxifloxacin, SXT, ciprofloxacin, cefoperazonesulbactam, ceftazidime, netilmicin, gentamicin and amikacin, respectively. For the 24 strains included in the combination study, the moxifloxacin minimal inhibitory concentration (MIC)50/MIC90 values were defined as 0.064/0.125 µg/mL (MIC range 0.023-4 µg/mL) and ceftazidime MIC50/MIC90 values were defined as 32/256 µg/mL (MIC range 1.5-256 µg/mL). According to the results of fractional inhibitor concentration (FIC) index; ceftazidime and moxifloxacin combination displayed synergism, additivity and indifference for 1 (4%), 18 (75%) and 5 (21%) strains, respectively and there was no antagonism. The FIC50/ FIC90 value is calculated as 0.75/1.01 (FIC range 0.5-1.01). Conclusions: SXT resistance in S. maltophilia strains is below 10%, but it should be closely monitored because of the limited treatment options. Tigecycline and moxifloxacin can be among the treatment alternatives because of their high sensitivity rates similar to SXT. The combination of moxifloxacin plus ceftazidime demonstrated in vitro synergism or additivity against majority of the strains. So, this combination may be used as an alternative for the treatment of patients with S. maltophilia infections if there is resistance or side effects to the antibiotics used as the first option. [ABSTRACT FROM AUTHOR]