2189. Colistin Heteroresistance in Enterobacter due to Base Heterozygosity at Certain phoPQ Locations

Abstract

Abstract Background Enterobacter species are major nosocomial pathogens, and the clinical implications and mechanisms of colistin heteroresistance (CHR) in Enterobacter remain unclear. Methods We used the population analysis profile (PAP) assay to determine the presence of CHR in Enterobacter. To examine whether CHR leads to treatment failure, we conducted in vitro time-killing assays and in vivo assays using murine intra-abdominal infection models. To determine the genetic mechanism for the CHR phenotype, we conducted whole-genome sequencing and ultra-deep second-generation sequencing. A schematic outline of methods and main results Results In this study, we found that 30% of Enterobacter clinical strains causing bloodstream infections at West China Hospital exhibited CHR, which was associated with treatment failure and fatal infections, as demonstrated by in vitro time-kill tests and in vivo mouse infection modeling. We identified base alterations in the phoP-phoQ gene as the main resistance mechanism in Enterobacter CHR and that this heterogeneity originated from colistin selection and base heterozygosity, as detected by ultra-deep second-generation sequencing. We also found that several different resistance subpopulations existed simultaneously in the same strain with different resistance mechanisms. Time-kill experiments in Enterobacter isolates with CHR or susceptible to colistin CHR strains lead to in vivo colistin treatment failure Phenotypic and genomic study of a CHR strain Conclusion We presented evidence for "genetic heterogeneity" in Enterobacter CHR strains, which is consistent with "phenotypic heterogeneity" and genetically explains the unstable and transient HR. This provides important insights and a fresh perspective into the mechanisms and clinical implications of Enterobacter CHR and underscores the importance of deep sequencing, prompting the research of high-throughput microbial single-cell sequencing as a method for detecting "genetic heterogeneity." Frequency of bases that mediate colistin resistance at the same locus of phoP-Q in the parental and resistant strains Disclosures All Authors: No reported disclosures