156. Using Whole Genome Sequencing to Genetically Profile and Analyze Escherichia coli Isolates with Varying Resistance to β-Lactam/β-lactamase Inhibitor Combinations

Background Whole-genome sequencing has gained interest for assessing antimicrobial resistance (AMR). However, multiple studies have shown a poor correlation between the β-lactam/β-lactamase inhibitor (BL/BLI) phenotype and β-lactamase gene presence/absence. In a recent publication, we found that amplification of β-lactamase encoding genes potentially contribute to BL/BLI resistance and here we explore if gene amplifications allow for better BL/BLI genotype/phenotype correlations. Methods We selected 109 E. coli bacteremia isolates and performed ETests (bioMerieux, Inc) to determine AST profiles using the following BL/BLI antibiotics: ampicillin/sulbactam (SAM), amoxicillin/clavulanic acid (AMC), and piperacillin/tazobactam (TZP). CLSI M100 guidelines (2018) were used to stratify isolates into 4 groups: SAM/AMC/TZP susceptible (Group 1), SAM resistant only (Group 2), SAM/AMC resistant (Group 3), and SAM/AMC/TZP resistant (Group 4). Short-read whole genome sequencing was performed on these isolates and analyzed by identifying AMR genes, establishing multi-locus sequence type (MLST), estimating copy number variants (CNV), and investigating blaTEM-1 promoter regions in relation to phenotype. A t-Distributed Stochastic Neighbor Embedding (t-SNE) clustering method and a core-genome, maximum-likelihood phylogeny was generated to group isolates based on AMR gene content and CNV data. Results We found 34 different MLST groups with the three most common sequence types ST131 (n=41), ST1193 (n=12), and ST648 (n=6). Group 1 and Group 2 isolates had similar copy number estimates of β-lactamase blaTEM-1 (1.8X and 1.5X respectively) while there was an increase for both Group 3 (3.7X) and Group 4 (8.2X) isolates (Table 1). Additionally, blaOXA-1 was primarily present in Group 4 isolates (63%) with elevated copy numbers (5.2X). We did not observe associations of blaTEM-1 promoter regions with each of the BL/BLI Groups. Our t-SNE analysis shows that Group 1, Group 3, and Group 4 isolates cluster independently. Core Genome Maximum-likelihood Phylogeny. Midpoint-rooted core-genome maximum-likelihood phylogeny comparing core elements (MLST) to non core elements (CNV). AMR CNV and presence/absence associate better with BL/BLI phenotypes than do core elements. Conclusion There is a clear delineation between fully susceptible and fully resistant BL/BLI E. coli isolates when gene amplification and presence/absence of narrow-spectrum β-lactamases are considered, which should be considered for BL/BLI resistance prediction models. Disclosures David E. Greenberg, MD, Shionogi: Grant/Research Support.