142. Evaluation of Meropenem-Vaborbactam Susceptibility and Underlying Resistance Mechanisms among Clinical KPC-producing Klebsiella pneumoniae

Abstract Background Meropenem-vaborbactam (MV) is the first carbapenem/β-lactamase inhibitor combination developed to restore meropenem susceptibility against KPC-producing carbapenem-resistant Enterobacterales(CRE). Vaborbactam (VAB) potently inhibits Ambler class A and C β-lactamases by reversible covalent binding of boronate to serine side chains of β-lactamases. Resistance to MV in non-metallo-β-lactamase (MBL) producing Klebsiella pneumoniae (KP) isolates has been described but remains rare. We sought to identify the major molecular mechanisms associated with MV resistance in KPC-producing KP (KPC-KP) isolates. Methods Clinical isolates with elevated MV MICs were identified by the consult service. Additional clinical isolates with mutations in ompK35 or ompK36 genes were selected from a historic database. Isolates with MBL or OXA-48-like genes were excluded. Controls were comprised of MV susceptible KPC-KP isolates. MICs determination was done using Sensititre automated broth microdilution (BMD) according to CLSI. VAB and avibactam concentrations were held at 8 µg/ml and 4 µg/ml, respectively. Whole genome sequencing (WGS) was performed on all isolates. Genome libraries were prepared using Illumina Nextera XT and sequencing was performed on MiSeq and MinION. Results A total 119 KPC-KP isolates were included in the study. All isolates were resistant to meropenem. Twenty-one KPC-KP with elevated MV MICs were identified. All MV resistant isolates harbored mutations in ompK36 genes. Glycine/aspartate (GD 134-135) insertion, premature stop codon in ompK36 genes, and concomitantly elevated blaKPC copy number were predominant among MV resistant isolates. No insertion elements in ompK36 gene promoter region were found. Two MV resistant isolates exhibited unique mutations in blaKPC and envZ genes. See table for WGS and MIC results. Table 1.Whole genome sequencing and MICs of MV resistant KPC-KP isolatesα: Truncated at nodes 14 and 76, partial genotype consistent with blaSHV-12WT: Wild type*: Premature stop codonGD: Duplication of Glycine (G134) and Aspartate (D135)FS: Frameshift mutationins: insertionMEM: meropenemMVB: meropenem-vaborbactamCZA: ceftazidime-avibactamCFD: cefiderocolN/A: not availableTable 2.Whole genome sequencing and MICs of MV susceptible KPC-KP isolates Conclusion MV resistant KPC-KP isolates were reliably analyzed using WGS to reveal the contribution of omp gene mutations and blaKPC copy number to this phenotype. Elevated MV MICs were additionally recognized among clinical isolates from a historic database preceding MV availability. In the absence of MBL production, caution remains warranted with the use of MV empirically against KPC-KP due to non-β-lactamase mediated resistance mechanisms. Disclosures Daniel D. Rhoads, M.D. PhD, Luminex: Advisor/Consultant|Talis Biomedical: Advisor/Consultant|Thermo Fisher: Advisor/Consultant Federico Perez, M.D., Accelerate: Grant/Research Support|Merck: Grant/Research Support|Pfizer: Grant/Research Support Robert A. Bonomo, MD, NIH VA: Grant/Research Support|VenatoRx Merck Wockhardt Cystic Fibrosis Foundation: Grant/Research Support.