1842. Assessment of Patients with Amp-C Inducible Enterobacteriaceae with Susceptibility Changes During Therapy
Session: Poster Abstract Session: Antibacterial Susceptibility Surveillance
Saturday, October 29, 2016
Room: Poster Hall
  • Resistance on therapy ESCPM - ID Week.pdf (65.0 kB)
  • Background: Enterobacter spp., Serratia marcescens, Citrobacter freundii, Providencia spp., and Morganella morganii (ESCPM) encode for AmpC beta-lactamases on their chromosomes. AmpC expression is generally inducible, although derepressed mutants with constitutive high-level AmpC expression can emerge. It is unclear if induction or constitutive AmpC expression has an impact on clinical outcomes.

    Methods: This retrospective chart review compares patients with ESCPM infections that developed increased resistance on therapy to those that did not. Patients included were admitted to the hospital between January 1, 2012 and January 1, 2015 and had respiratory, blood, or intra-abdominal cultures positive for ESPCM pathogens. Patient characteristics were analyzed using Fisher’s exact test, 2-sided, and independent t-test. Statistical significance is defined as a p-value less than 0.05.

    Results: From a total of 328 treated ESCPM infections, 76 patients had repeat cultures positive for the same pathogen within 30 days of the index infection, and 18 exhibited changes in antibiotic susceptibilities. The mean time to repeat culture was 7.25 ± 6.2 days. Differences between patients with susceptibility changes and those without include frequency of E. aerogenes (44.4% vs. 20.7%, p=0.046) and S. marcescens infections (5.6% vs. 27.6%, p=0.050). Frequency of ceftriaxone susceptibility and site of infection were not statistically different. Clinical failure in patients with susceptibility changes occurred in 17%. There were no differences in 30-day mortality. The frequency of susceptibility changes based on empiric antibiotic group is in Table 1.

    Susceptibility changes (n/N)


    2/5 (40%)

    First generation cephalosporin or penicillin

    1/3 (33%)


    8/28 (29%)


    2/9 (22%)


    4/22 (18%)


    1/7 (14%)


    0/1 (0%)


    0/1 (0%)

    Conclusion: Only a subset of patients had repeat culture data to evaluate this which is consistent with most microbiology laboratory practice for repeat sensitivity testing. Susceptibility changes were more likely to occur in E. aerogenes. The susceptibility changes did not appear to impact clinical outcomes.

    Meghan Jeffres, PharmD1, Clayton Foster, MD2, Bruce Mccollister, MD3, Randolph Fujit, PharmD4, Mary Bessesen, MD4 and Michelle Barron, MD5, (1)Department of Clinical Pharmacy, University of Colorado Skaggs School of Pharmacy, Aurora, CO, (2)Division of Infectious Diseases, University of Colorado, Aurora, CO, (3)Division of Infectious Diseases, University of Colorado Denver, Aurora, CO, (4)VA Eastern Colorado Healthcare System, Denver, CO, (5)Internal Medicine/Infectious Diseases, University of Colorado Denver, Aurora, CO


    M. Jeffres, None

    C. Foster, None

    B. Mccollister, None

    R. Fujit, None

    M. Bessesen, None

    M. Barron, None

    Findings in the abstracts are embargoed until 12:01 a.m. CDT, Wednesday Oct. 26th with the exception of research findings presented at the IDWeek press conferences.