Lethal synergy involving bicyclomycin: An approach for reviving old antibiotics

Muhammad Malik, Liping Li, Xilin Zhao, Robert J. Kerns, James M. Berger, Karl Drlica

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Background: One way to address the growing problem of antimicrobial resistance is to revive old compounds that may have intrinsic lethal activity that is obscured by protective factors. Bicyclomycin is an old inhibitor of the Rho transcription terminator that by itself shows little rapid lethal activity. However, bicyclomycin participates in bacteriostatic synergy, which raises the possibility that conditions for lethal synergy may exist, perhaps through a suppression of protective factors. Methods: Bicyclomycin was combined with bacteriostatic inhibitors of gene expression, and bactericidal activity was measured with several cultured Gram-negative pathogens. Results: When used alone, bicyclomycin failed to rapidly kill growing cultures of Escherichia coli; however, the additional presence of bacteriostatic concentrations of tetracycline, chloramphenicol or rifampicin led to rapid killing. Four other pathogen species, Acinetobacter baumannii, Klebsiella pneumoniae, Salmonella enterica serotype Typhimurium and Shigella dysenteriae, also exhibited enhanced killing when bicyclomycin was combined with tetracycline or rifampicin. This lethal synergy was achieved at low concentrations (slightly above the MIC) for all agents tested in combinations. Follow-up work with E. coli indicated that lethal synergy arose from a blockage of transcription elongation. Moreover, lethal synergy was reduced when bicyclomycin was added 60 min before tetracycline, suggesting that bicyclomycin induces a protective factor. Conclusions: The action of bicyclomycin illustrates the potential present in a largely abandoned antibacterial agent; it exhibits lethal synergy when coadministered with known, bacteriostatic inhibitors of gene expression. The identification of protective factors, which are currently uncharacterized, may reveal newways to promote the lethal action of some old antibiotics.

Original languageEnglish (US)
Pages (from-to)3227-3235
Number of pages9
JournalJournal of Antimicrobial Chemotherapy
Issue number12
StatePublished - Dec 1 2014


  • Acinetobacter baumannii
  • Back-tracking
  • Escherichia coli
  • Gene expression inhibitors
  • Klebsiella pneumoniae
  • Transcription elongation complex

ASJC Scopus subject areas

  • Pharmacology
  • Microbiology (medical)
  • Infectious Diseases
  • Pharmacology (medical)


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