1454. Plazomicin Activity against Enterobacterales Isolates Producing Extended-Spectrum β-Lactamases (ESBLs), Carbapenemases, and Aminoglycoside-Modifying Enzymes (AMEs) from United States (US) Hospitals

Background Limited therapeutic options are available for the treatment of multidrug resistant (MDR) organisms. Plazomicin (PLZ) is an aminoglycoside developed to overcome common aminoglycoside-resistance mechanisms. We evaluated the activity of PLZ and comparators against Enterobacterales isolates collected in 2018-2019 carrying genes encoding ESBLs, carbapenemases, and AMEs. Methods Among 3,899 Enterobacterales isolates from US hospitals susceptibility (S) tested using reference broth microdilution method, 619 isolates from selected species displaying elevated MIC values for cephalosporins, carbapenems and/or resistance (CLSI criteria) to amikacin (AMK), gentamicin (GEN) and tobramycin (TOB) were submitted to whole genome sequencing for detection of resistance genes. Results Most isolates producing ESBLs (n= 418) carried blaCTX-M (n= 386). The activity of PLZ (99.3% susceptible [S]) was comparable to that of colistin and higher than other comparators against ESBL isolates (Figure). AMK inhibited 96.4% of the isolates and GEN and TOB inhibited 57.9% and 43.5%, respectively. Only 34 isolates produced carbapenemases, including 19 KPC-2, 10 KPC-3, 1 each with VIM-1, OXA-181, NDM-5 and KPC-2-like plus 1 isolate carrying the genes encoding NDM-1 and OXA-232. These isolates displayed higher resistance rates to comparators and only PLZ, and tigecycline inhibited >90% of these isolates. AMK and GEN inhibited 67.6% and 55.9% of these isolates, respectively. PLZ was active against 97.7% of isolates carrying AME genes (n= 306) that carried aac(6’)-Ib-cr (n =177), aac(3)-IIa (n = 159) and aac(3)-IId (n =81), among others. Most of these isolates were resistant to GEN and TOB (only 10.8-14.1% S), but 92.8% were S to AMK. Three K. pneumoniae isolates carried 16S rRNA methyltransferases, 1 armA (also harboring NDM-1) and 2 rmtB1. Conclusion The activity of PLZ against Enterobacteriaceae isolates carrying AMEs, ESBLs, and carbapenemases was greater than the activity of other aminoglycosides tested and comparable to those of tigecycline and colistin against carbapenemase-producing organisms. Isolates carrying genes encoding ESBLs, AMEs and carbapenemases are usually MDR and PLZ had activity against these organisms collected in the US. Figure 1 Disclosures Mariana Castanheira, PhD, 1928 Diagnostics (Research Grant or Support)A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Amplyx Pharmaceuticals (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Fox Chase Chemical Diversity Center (Research Grant or Support)GlaxoSmithKline (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support)Pfizer (Research Grant or Support)Qpex Biopharma (Research Grant or Support) Rodrigo E. Mendes, PhD, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Basilea Pharmaceutica International, Ltd (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Department of Health and Human Services (Research Grant or Support)GlaxoSmithKline (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Pfizer (Research Grant or Support) Timothy B. Doyle, Allergan (Research Grant or Support)Allergan (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Pfizer (Research Grant or Support)Qpex Biopharma (Research Grant or Support) Valerie Kantro, n/a, Cipla Ltd. (Research Grant or Support) Helio S. Sader, MD, PhD, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Melinta (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support)Pfizer (Research Grant or Support) Jaideep Gogtay, n/a, Cipla Ltd. (Employee) Sandhya Das, n/a, Cipla Ltd. (Research Grant or Support)