Scientific Poster Session III - Research Fellowship Platform

Research Fellowship Platform Applicants
  Monday, October 14, 2024
  01:00 PM–02:30 PM

Abstract

Introduction: Heteroresistance is a phenomenon where subpopulations of bacteria display varying levels of antimicrobial susceptibility; it is often undetected by standard susceptibility testing which leads to therapeutic failures. Vancomycin (VAN) is one of the treatment options for enterococcal infections. Heteroresistant vancomycin-intermediate Staphylococcus aureus has been well-documented however, there is limited published data for VAN heteroresistance enterococci.

Research Question or Hypothesis: Evaluate the prevalence of VAN heteroresistance among clinical enterococcal isolates.

Study Design: In vitro

Methods: Clinical enterococci isolates (65) were obtained across health systems in Phoenix, AZ and Atlanta, GA. Minimum inhibitory concentration (MIC) was determined using broth microdilutions according to CLSI. All isolates were screened for heteroresistance using Brain Heart Infusion agar (BHI, BD Biosciences, Franklin Lakes, NJ) containing VAN 6 and 8 µg/mL (BHI-V6/BHI-V8) and standard VAN Etest (Liofilchem Inc, Waltham, MA). Plates were incubated at 37°C for 48 hours (h). Modified population analysis profile (PAP) was performed as described by Pfeltz RF et al using various VAN concentrations. Sensitivity and specificity analyses were used to compare BHI-V6 vs BHI-V8 and standard Etest using PAP as reference.

Results: VAN MIC_50/90 was 1 and 2 µg/mL for both broth microdilution (range 0.25-4 µg/mL) and VAN Etest (range 0.25-2 µg/mL). Standard VAN Etest detected 6.1% (4/65) heteroresistant. BHI-V6/BHI-V8 plates both detected 10.7% (7/65) strains to be heteroresistant. PAP confirmed 6.1% (4/65) to be heteroresistant. VAN Etest and BHI-V6/BHI-V8 demonstrated a 100% sensitivity; however, specificity was higher with VAN Etest compared to BHI-V6/BHI-V8 (100% vs 95%). BHI-V6/BHI-V8 both falsely identified 4.6% (3/65) heteroresistance.

Conclusion: Our study demonstrated the prevalence of heteroresistance among enterococci to be 6.1%. Further study is warranted in the future to understand VAN heteroresistance among enterococci

Presenting Author

Howard Chhen PharmD
Midwestern University College of Pharmacy - Glendale Campus

Authors

Vanthida Huang Pharm.D., BSPHM, FCCP
Midwestern University, College of Pharmacy-Glendale

Tho Pham PharmD, BCIDP
University of Arizona R Ken Coit College of Pharmacy

Chad M. VanDenBerg Pharm.D., M.S, BCPP
Midwestern University College of Pharmacy-Glendale