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Background Serratia marcescens is a Gram-negative motile bacillus that is a facultative anaerobe and non-lactose fermenting. Serratia can be isolated from water, soil, plants, and the intestinal microbiome. Serratia produces a unique Identifying reddish pigment called prodigiosin. Serratia is responsible for only 0.14% of infective endocarditis cases, with a mortality rate of 85%. Methods A 37 YO female with a history of Intravenous heroin abuse was admitted with fevers and dyspnea. Vital signs were BP 76/50, HR 140, RR 26, temp 102 F, and SpO2 98% on room air. She was toxic-appearing. Labs: WBC 26000(4,000 – 11,000 /uL) with 14% bands, Hb 5.6 (12.6 – 17.0 g/dL), PLT 15*10^3(150-372*10^3/uL), creatinine 2.5 (0.50 - 1.60 mg/dL), lactic acid 15.8 (0.5-2.2 mmol/L). We started vancomycin, piperacillin-tazobactam, and norepinephrine for septic shock. A transthoracic echo showed a large mass on the tricuspid valve, and a transesophageal echo depicted it as vegetation. Blood cultures grew Serratia. She underwent excision of anterior and posterior tricuspid valve leaflets with reconstruction and ring annuloplasty. She reported washing her syringes with tab water and reusing them again. Serratia has a predilection for left-side heart valves even in the IVDU population but this patient presented with a tricuspid valve endocarditis. Results Serratia is a rare cause for IE in the ICE study; out of 2.761 definite IE cases identified over five years, only forty-nine instances were due to gram-negative bacilli. Of those, only four cases were due to Serratia. The clinical presentation of Serratia includes constitutional symptoms, new-onset murmur, and cutaneous and neurologic manifestations. Serratia produces multiple pathogenic factors allowing Serratia to result in valvular destruction and perivalvular complications, and distant septic emboli metastasis. Conclusion Serratia is sensitive to third and fourth-generation cephalosporins, monobactams, carbapenems, fluoroquinolones, and aminoglycosides. Treatment is complex due to the production of AmpC B-lactamase, which hydrolyzes third and fourth-generation cephalosporins. The 2005 IDSA suggested a combination of B-lactam and an aminoglycoside for Serratia endocarditis, and these are not guidelines but merely recommendations. Disclosures All Authors: No reported disclosures.