Validation of a High-Throughput Screening Assay for Identification of Adjunctive and Directly Acting Antimicrobials Targeting Carbapenem-Resistant Enterobacteriaceae

Assay Drug Dev Technol. 2016 Apr;14(3):194-206. doi: 10.1089/adt.2016.701. Epub 2016 Apr 5.


We describe development and validation of a high-throughput screen (HTS) for identifying small molecules that restore the efficacy of carbapenems (adjunctives) and/or directly inhibit growth of carbapenem-resistant Enterobacteriaceae (CRE). Our HTS assay is based on a screen-counterscreen approach using a representative multidrug-resistant CRE strain, Klebsiella pneumoniae BIDMC12A. Specifically, we tested the ability of small molecules to inhibit bacterial growth in the presence (screen) or absence (counterscreen) of meropenem, a representative carbapenem antibiotic. Primary screening of 11,698 known bioactive compounds identified 14 with adjunctive activity and 79 with direct antimicrobial effect. Secondary screening identified triclosan as a strongly synergistic meropenem adjunctive (fractional inhibitory concentration = 0.48) and confirmed azidothymidine (AZT) (minimal inhibitory concentration [MIC] = 4 μg mL(-1)), NH125 (MIC = 4 μg mL(-1)), diphenyleneiodonium chloride (MIC = 8 μg mL(-1)), and spectinomycin (MIC = 32 μg mL(-1)) as potent direct antimicrobials. Spectrum of activity of AZT and spectinomycin was tested against a collection of 103 representative Enterobacteriaceae strains (≈50% CRE). AZT, a nucleoside analog used to treat human immunodeficiency virus, demonstrated an MIC50 of 2 μg mL(-1). Spectinomycin, an antibiotic used to treat gonorrhea, had an MIC50 of 32 μg mL(-1). Therefore, a significant percentage of CRE strains appeared relatively susceptible to these antimicrobials. These data identified AZT and spectinomycin as available agents warranting further study for potential treatment of multidrug-resistant CRE infection. Our results provide proof of principle and impetus for performing a large-scale HTS for discovery of novel, small-molecule adjunctives and antibacterial agents directly targeting CRE.

Publication types

  • Research Support, N.I.H., Extramural
  • Validation Study

MeSH terms

  • Anti-Bacterial Agents / analysis*
  • Anti-Bacterial Agents / pharmacology*
  • Carbapenems / pharmacology*
  • Dose-Response Relationship, Drug
  • Drug Resistance, Bacterial / drug effects*
  • Enterobacteriaceae / drug effects*
  • Enterobacteriaceae / growth & development
  • High-Throughput Screening Assays*
  • Microbial Sensitivity Tests
  • Small Molecule Libraries / analysis
  • Small Molecule Libraries / pharmacology*
  • Structure-Activity Relationship


  • Anti-Bacterial Agents
  • Carbapenems
  • Small Molecule Libraries