Stenotrophomonas maltophilia Resistance in Military Trauma Patients

Background: Stenotrophomonas maltophilia is as an emerging pathogen in critically ill trauma patients. This study identifies S. maltophiliadistribution, susceptibility, and risk factors for resistance in a military trauma population.

Methods: All S. maltophilia isolates prospectively collected during the Trauma Infectious Disease Outcomes Study (TIDOS ) were included (9/09-9/14). Unique initial isolates were defined as differing in site, resistance and pulse-field gel electrophoresis (PFGE) patterns; serial isolates as ≥7 days between isolation. BD Phoenix™BD Emerge™(NMIC300) panels were used for susceptibility testing. Clonality was assessed with PFGE. Demographics, trauma-related characteristics, isolate source, presence of polymicrobial infection, and antimicrobial exposure before and after initial isolation were evaluated. Susceptibilities were defined by CLSI criteria [trimethoprim-sulfamethoxazole (TS), ticarcillin-clavulanate (TC), ceftazidime (CZ), levofloxacin (LV) minocycline (MC)] or MIC [moxifloxacin (MX), ciprofloxacin (CP), tigecycline (TG)].

Results: Of 2,699 TIDOS patients, 66 patients with 67 unique initial isolates were included. Sources were wound (62%), respiratory (27%), blood (7%), urine (1%), and other (3%) with 72% resistant to ≥1 antimicrobial. There was no evidence of clonal spread by PFGE. There was a trend towards increased resistance in wound isolates and patients with injury severity scores (ISS) >25 (p=0.05). Higher initial CP MICs were associated with increasing time from injury to initial isolate (p=0.01). CZ resistance was associated with LV resistance, and higher MX, CP, and TG MICs (p<0.01). Of 9 patients identified with 26 unique serial isolates, all had an ISS >25 and resistance to ≥1 antimicrobial. Comparing all initial to serial isolates, susceptibilities decreased for TS (from 99% to 81%), CZ (42% to 4%), LV (82% to 31%), and TC (67% to 31%). All isolates remained susceptible to MC. Initial and serial isolate MICs for CP, MX, and TG were ≤2µg/mL in 28% and 8%, ≤4µg/mL in 97% and 89% and ≤2µg/mL in 86% and 23% respectively.

Conclusion: S. maltophilia resistance in trauma patients may be seen with higher injury severity, increased time from injury to isolation, and in serial isolates.