2430. Impact of USCAST proposed breakpoint changes to aminoglycosides, cyclines, and levofloxacin on carbapenem-resistant Enterobacteriaceae at a U.S. tertiary referral academic medical center
Session: Poster Abstract Session: Treatment of AMR Infections
Saturday, October 6, 2018
Room: S Poster Hall
  • USCAST Poster.pdf (355.2 kB)
  • Background: USCAST is one of many national committees that establish standards for testing and interpreting antimicrobial susceptibility. While working closely with EUCAST, USCAST has proposed updated breakpoints for the aminoglycosides, fluoroquinolones, and tigecycline and is discussing updated breakpoints for the tetracycline antimicrobials. A majority of U.S. hospitals currently utilize FDA or CLSI breakpoints. This study sought to determine the impact of the proposed updated breakpoints on a population of carbapenem-resistant Enterobacteriaceae at a U.S. tertiary referral academic medical center.

    Methods: Carbapenem-resistant Enterobacteriaceae (n=122) from January 2012 – January 2017 were identified as part of routine patient care for study inclusion. Amikacin, gentamicin, tobramycin, levofloxacin, minocycline and tigecycline were evaluated in duplicate on at least two separate occasions by broth microdilution according to CLSI guidelines. The most conservative minocycline breakpoint (≤1 mg/L) being discussed by USCAST was utilized for analysis. McNemar’s test determined significant susceptibility changes between USCAST and FDA/CLSI breakpoints for all CRE and for K. pneumoniae and Enterobacter spp.

    Results: K. pneumoniae (n=58; 48%) and Enterobacter spp. (n=40; 33%) comprised the majority of CRE.

    Table 1: CRE susceptibility



    % Susceptibility (Breakpoint)


     % Susceptibility (Breakpoint)


    % Susceptibility (Breakpoint)




    66% (8)

    86% (16)

    55% (4)



    21% (2)

    31% (4)

    21% (2)



    15% (2)

    18% (4)

    14% (1)





    16% (4)

    1% (1)



    43% (1)

    84% (2)

    43% (1)




    6% (0.5)

    15% (2)

    6% (0.5)


    P-values <0.05 are significant and indicate differences between CLSI/FDA and USCAST susceptibility

    Conclusion: Implementation of the proposed USCAST susceptibility breakpoints will impact clinician antimicrobial choice regarding the treatment of infections caused by CRE. Amikacin and tigecycline susceptibility markedly decreased when utilizing the proposed USCAST breakpoints.

    Brandon Kulengowski, PharmD, MS1, Gretchen Ingling, PharmD Candidate1, Kristen E. Wilhite, PharmD Candidate1 and David S. Burgess, PharmD, FCCP, FIDP2, (1)University of Kentucky, College of Pharmacy, Lexington, KY, (2)University of Kentucky College of Pharmacy, Lexington, KY


    B. Kulengowski, None

    G. Ingling, None

    K. E. Wilhite, None

    D. S. Burgess, None

    Findings in the abstracts are embargoed until 12:01 a.m. PDT, Wednesday Oct. 3rd with the exception of research findings presented at the IDWeek press conferences.