2134. Differential Changes in Breath Volatile Metabolites to Identify Carbapenem-Resistant Enterobacteriaceae (CRE) in a Murine Pneumonia Model

BACKGROUND: CRE infections cause significant mortality, in large part because rapid identification of these infections is challenging. We tested the hypothesis that CRE and their isogenic carbapenem-susceptible counterparts have differential metabolic responses to carbapenem therapy. METHODS: We generated isogenic pairs of E. coli, E. cloacae, and K. pneumoniae by inserting a bla(NDM-1)-containing plasmid into carbapenem-susceptible E. coli, E. cloacae, and K. pneumoniae. We confirmed phenotypic meropenem (MPM) resistance per CLSI breakpoints for Enterobacteriaceae (MIC ≥4) in the NDM-1(+) member and susceptibility (MIC≤1) in the NDM-1(-) member of each pair. We administered 2 × 10(8) CFU of each isolate intranasally to 23–28 g male C57BL/6J mice, infecting 6 mice with the NDM-1(+) member and 6 with the NDM-1(−) member of each species pair (12 mice per bacterial species). 24 hours after infection, we treated 3 mice in each NDM-1(+) and NDM-1(−) bacterial species cohort with MPM over 4 hours, and the other 3 mice in each cohort with saline over 4 hours as controls, confirming adequate infection (a target of 10(6) CFU/g of lung tissue) in quantitative lung homogenate cultures. We then collected breath samples from each mouse via tracheostomy using a murine ventilator, identifying all volatile metabolites in each sample using thermal desorption-gas chromatography/tandem mass spectrometry. We used Wilcoxon tests to examine differences in metabolite abundance between MPM and saline-treated control mice in the NDM-1(+) and NDM-1(−) a member of each species pair, with a two-sided P-value threshold of < 0.1. RESULTS: Several breath volatile metabolites changed differentially within each NDM-1(+)/NDM-1(-) pair, outlined in Table 1 (E. coli), Table 2 (E. cloacae), and Table 3 (K. pneumoniae). Each listed metabolite that changed with MPM did not change with MPM in mice infected with each isogenic counterpart CONCLUSION: There are differential in vivo metabolic responses with effective vs. ineffective treatment of mice with pneumonia caused by E. coli, E. cloacae, and K. pneumoniae pairs that are genetically identical other than bla(NDM-1); this differential treatment response can potentially be used to identify these infections. [Image: see text] [Image: see text] [Image: see text] DISCLOSURES: All authors: No reported disclosures.