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Published on: April 18, 2019
Antimicrobial susceptibility and combination testing of invasive Stenotrophomonas maltophilia isolates
Deirdre Church1, Tracie Lloyd, Gisele Peirano
1Division of Microbiology, Calgary Laboratory Services, Calgary, Alberta, Canada.
Background:
Treatment of invasive Stenotrophomonas maltophilia infections is difficult due to this organism's inherent multidrug resistance and increasing resistance to trimethoprim-sulfamethoxazole via acquisition of the sul genes.
Methods:
In vitro antibiotic susceptibility testing was performed using a customized broth microdilution panel. Combination testing for tigecycline with anti-Stenotrophomonas agents (i.e. colistin, ticarcillin-clavulanate, ceftazidime, and levofloxacin) was done using the cross Etest method. Genotyping was done using automated repetitive PCR.
Results:
A total of 90 patients with invasive S. maltophilia infections included: (79%) adults, and 21% children or infants [6/12 (50%) cases occurred in infants aged ≤ 1 year.]. S. maltophilia isolates were recovered from blood (69%), lower respiratory (21%) or other sites (CSF, peritoneal fluid) (11%). Seventeen percent of the isolates were SXT-R, and also demonstrated multi-drug resistant to two or more antibiotic classes. Minocycline, tigecycline and colistin had the best in vitro activities. The combination testing of tigecycline and colistin gave the best results; 12 isolates were tested and synergy occurred in 3 isolates while an additional 7 isolates showed additive results.
Conclusions:
We recommend further evaluation with killing assays and clinical studies to evaluate the effectiveness of tigecycline and colistin combination for invasive S. maltophilia infections.
Insights
Treatment of invasive Stenotrophomonas maltophilia infections is challenging due to multidrug resistance. Tigecycline and colistin combination therapy shows promising in vitro activity, warranting further clinical evaluation for Stenotrophomonas maltophilia infections.
Area of Science:
- Infectious Diseases
- Medical Microbiology
- Antimicrobial Resistance
Background:
- Invasive Stenotrophomonas maltophilia infections present treatment challenges due to inherent multidrug resistance.
- Increasing resistance to trimethoprim-sulfamethoxazole (SXT-R) is observed, often linked to sul gene acquisition.
Purpose of the Study:
- To evaluate the in vitro activity of tigecycline in combination with other agents against Stenotrophomonas maltophilia.
- To assess the efficacy of tigecycline-colistin combination for invasive S. maltophilia infections.
Main Methods:
- Antibiotic susceptibility testing using broth microdilution and cross Etest for combination testing.
- Genotyping of S. maltophilia isolates was performed using automated repetitive PCR.
- In vitro activity of minocycline, tigecycline, and colistin was assessed against 90 patient isolates.
Main Results:
- Minocycline, tigecycline, and colistin demonstrated the best in vitro activity against S. maltophilia isolates.
- The tigecycline-colistin combination showed synergistic or additive effects in 10 out of 12 tested isolates.
- Seventeen percent of isolates were trimethoprim-sulfamethoxazole resistant and multidrug resistant.
Conclusions:
- The combination of tigecycline and colistin exhibits promising in vitro activity against Stenotrophomonas maltophilia.
- Further investigation through killing assays and clinical studies is recommended to validate the efficacy of this combination therapy.
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