162. The Genotypic Antibiogram: Using Results of Gram-Negative Antimicrobial Resistance Genes Identified via Rapid Blood Culture Identification Tests to Optimize Treatment of Enterobacterales Bloodstream Infections

Abstract Background With the increasing incidence of infections from Enterobacterales resistant to commonly used antibiotics, rapid diagnostic tests, such as BioFire’s Blood Culture Identification 2 (BCID2) multiplex PCR panel, can be utilized to detect potential antimicrobial resistance more rapidly and help direct more appropriate empiric therapy. We describe the epidemiology of Enterobacterales bloodstream infection (BSI), associated antimicrobial resistance genes using BCID2, and subsequent susceptibility patterns at an academic medical center to develop a genotypic antibiogram. Methods We reviewed all positive BCID2 results at Nebraska Medical Center from 8/1/2021–11/1/2022. Only monomicrobial Enterobacterales BSI were included. Patient demographics, antimicrobial resistance markers, BCID2, culture, and susceptibility results were assessed. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of blaCTX-M marker were compared to ceftriaxone susceptibility patterns. Results We reviewed 456 unique Enterobacterales isolates, of which 236 were from male patients (52%), 189 (41%) immunocompromised patients, and 342 (75%) community onset. The most common species identified were Escherichia coli (55%) and Klebsiella pneumoniae (17%). blaCTX-M was detected in 49 (11%) isolates, with 41 (84%) E. coli and 6 (12%) K. pneumoniae. blaKPC was detected in 2 isolates (1 K. oxytoca and 1 K. variicola), but no other carbapenemase genes were detected. blaCTX-M sensitivity and specificity for detection of ceftriaxone resistance was 83% and 100%, respectively. blaCTX-M PPV for ceftriaxone resistance was 100%, while the NPV of absent blaCTX-M for ceftriaxone susceptibility was 97%. Conclusion Locally, the majority of ceftriaxone-resistant E. coli and Klebsiella BSIs harbor blaCTX-M, while carbapenemases are rare. Utilization of rapid diagnostics can optimize antimicrobial therapy for Enterobacterales by creation of a genotypic antibiogram. Disclosures Scott J. Bergman, PharmD, bioMerieux, Inc.: Honoraria Trevor C. Van Schooneveld, MD, FSHEA, FACP, AN2 Therapeutics: Grant/Research Support|Biomeriuex: Advisor/Consultant|Biomeriuex: Grant/Research Support|Insmed: Grant/Research Support|Thermo-Fischer: Honoraria