1607. Dual Therapy with Aztreonam & Ceftazidime/Avibactam Against Multi-Drug Resistant Stenotrophomonas maltophilia on Tricuspid Valve Endocarditis

BACKGROUND: Antimicrobial resistance in Stenotrophomonas maltophilia is one of the most complex among Gram-negatives. Presence of regulating non-specific antimicrobial class efflux pumps and chromosomal encoded L1 metallo-betalactamase (Ambler Class B) and L2 betalactamase (Ambler Class A) are responsible for few clinically active antimicrobials and pan-drug resistant strains. METHODS: A 38 year old male with a history of IV drug use, chronic hepatitis C, and recent MSSA endocarditis was admitted with sepsis. Workup revealed tricuspid valve endocarditis with pulmonary septic emboli due to S. maltophilia. Initial antibiotics were levofloxacin (LVX), metronidazole, and piperacillin-tazobactam (TZP) followed by LVX and minocycline (MIN). He had valve replacement on day 6. Repeat blood cultures and valve tissue culture revealed pan-resistant S. maltophilia (resistant: ceftazidime (CAZ), LVX, MIN, TMP/SMX, chloramphenicol; intermediate: MIN; eravacycline MIC 8 μg/mL; tigecycline MIC 16 μg/mL). Microbiology Department was consulted for additional antimicrobial options. In vitro testing for aztreonam (ATM) with ceftazidime/avibactam (CZA) was recommended. RESULTS: Synergy testing between ATM and CZA was performed by positioning ATM strip over the area where CZA had been previously been placed and removed after 10 minutes of incubation. The interception of the growth with the ATM strip was read. In presence of avibactam, ATM MIC was 4 μg/mL, 6 two-fold dilutions lower than ATM without CZA. MIC for ATM (256 μg/mL), CAZ (256 μg/mL) and CZA (32 μg/mL) were tested individually. ATM with CZA was recommended as a salvage treatment based on in vitro result. Patient completed 6 weeks of ATM with CZA along with MIN. He achieved microbiologic clearance and clinical recovery from infection. At the end of treatment, he experienced episodes of refractory ascites. With complex comorbidities, patient was not a transplant candidate and transitioned to hospice two weeks later. CONCLUSION: Although the surgical excision was key, treatment with ATM and CZA provided effective antimicrobial treatment in the setting of persistent positive blood culture. ATM with CZA should be considered for cases of pan-drug resistant S. maltophilia with limited treatment options. DISCLOSURES: All Authors: No reported disclosures