Discovery and Characterization of a Nitroreductase Capable of Conferring Bacterial Resistance to Chloramphenicol

Terence Spencer Crofts*, Pratyush Sontha, Amber O. King, Bin Wang, Brent A. Biddy, Nicole Zanolli, John Gaumnitz, Gautam Dantas

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

39 Scopus citations


Widespread antibiotic resistance has led to the reappraisal of abandoned antibiotics including chloramphenicol. However, enzyme(s) underlying one form of chloramphenicol resistance, nitroreduction, have eluded identification. Here we demonstrate that expression of the Haemophilus influenzae nitroreductase gene nfsB confers chloramphenicol resistance in Escherichia coli. We characterized the enzymatic product of H. influenzae NfsB acting on chloramphenicol and found it to be amino-chloramphenicol. Kinetic analysis revealed reduction of diverse substrates including the incomplete reduction of 5-nitro antibiotics metronidazole and nitrofurantoin, likely resulting in activation of these antibiotic pro-drugs to their cytotoxic forms. We observed that expression of the H. influenzae nfsB gene in E. coli results in significantly increased susceptibility to metronidazole. Finally, we found that in this strain metronidazole attenuates chloramphenicol resistance synergistically, and in vitro metronidazole weakly inhibits chloramphenicol reduction by NfsB. Our findings reveal the underpinnings of a chloramphenicol resistance mechanism nearly 70 years after its description.

Original languageEnglish (US)
Pages (from-to)559-570.e6
JournalCell Chemical Biology
Issue number4
StatePublished - Apr 18 2019


  • E. cloacae
  • H. influenzae
  • amphenicols
  • antibiotics
  • chloramphenicol
  • metronidazole
  • nfsB
  • nitroreductase
  • resistance
  • synergy

ASJC Scopus subject areas

  • Drug Discovery
  • Molecular Medicine
  • Molecular Biology
  • Biochemistry
  • Clinical Biochemistry
  • Pharmacology


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