1183. Assessment of Antibiotic Resistance Genes, Phenotypic Expression and Association with Antibiotic Exposure in Serial E. coli Isolates Recovered from Combat-Injured U.S. Military Service Members
Session: Poster Abstract Session: Resistance Mechanisms
Friday, October 9, 2015
Room: Poster Hall
  • Poster 1183 - Mende et al sm.png (393.6 kB)
  • Background: E. coli is the most common colonizing (~40% ESBL) and infecting (~75% ESBL) organism recovered from U.S. service members with combat-related traumatic injuries in the Trauma Infectious Disease Outcome Study (TIDOS). Plasmids encoding ESBLs may contain other antibiotic resistance genes (RG) which could exert selection pressure when exposed to antibiotics. This study evaluates RG of E. coli isolates and their association with antibiotic exposure to better understand the resistance mechanisms, and their impact on the outcomes of infections.

    Methods: Previously characterized serial E. coli isolates collected for TIDOS were utilized for whole genome sequencing. RG were identified using web-based microbial annotation resources and pipelines developed by the MRSN. Plasmid profiling was determined by PFGE S1 digestion. Susceptibility to aminoglycosides (AG), beta-lactams (BL), and fluoroquinolones (FQ), antimicrobial exposure and infection outcome data were extracted from the TIDOS database.

    Results: 49 serial isolates from 10 patients were sequenced. 24 unique strains were identified and their initial isolates (79% ESBL, 38% infecting) were used for data analysis. All 19 ESBL strains carried 1 ESBL-encoding gene each, 16 carried 1-2 additional BL-RG and all were non-susceptible (NS) to BL. 4 of the 5 non-ESBL carried 1-2 other BL-RG. All 24 strains had been exposed to cefazolin with 20 being NS, and 5 strains to piperacillin-tazobactam with 2 being NS. 14 strains were susceptible (S) to all tested AG, 10 were NS to 1 or 2 AG, 22 (including 12 S) carried 1-5 AG-RG, and none had exposure to AG. 18 strains were NS to FQ, 14 (including 3 S) carried 1 FQ-RG, and 4 NS were exposed to FQ. For the 9 infecting strains, infection was cleared for 45%, infection progressed for 33%, and infection was ongoing at discharge for 22%.

    Conclusion: The presence of resistance genes is not an indicator of phenotypic expression. Numerous strains carry resistances genes but are S to corresponding antibiotics. Three strains could have acquired resistance genes due to antibiotic exposure. Due to low sample numbers and most strains being collected prior antibiotic treatment further studies are needed to better define the association with antibiotic exposure and clinical outcomes.

    Katrin Mende, PhD1,2, Erik Snesrud, BS3, Fatma Onmus-Leone, MS3, Lakshmi Appalla, MS3, Mary Hinkle, M.D.3, Emil Lesho, DO, FIDSA3, Ping Li, MS2, Clinton K. Murray, MD, FIDSA1 and David Tribble, MD, DrPH, FIDSA2, (1)San Antonio Military Medical Center, JBSA Fort Sam Houston, TX, (2)Infectious Disease Clinical Research Program, Uniformed Services University of the Health Sciences, Bethesda, MD, (3)Walter Reed Army Institute of Research, Silver Spring, MD


    K. Mende, None

    E. Snesrud, None

    F. Onmus-Leone, None

    L. Appalla, None

    M. Hinkle, None

    E. Lesho, None

    P. Li, None

    C. K. Murray, None

    D. Tribble, None

    Findings in the abstracts are embargoed until 12:01 a.m. PDT, Wednesday Oct. 7th with the exception of research findings presented at the IDWeek press conferences.