In vitro synergism of colistin and N-acetylcysteine against stenotrophomonas maltophilia

Nagaia Ciacci, Selene Boncompagni, Felice Valzano, Lisa Cariani, Stefano Aliberti, Francesco Blasi, Simona Pollini, Gian Maria Rossolini, Lucia Pallecchi

Research output: Contribution to journalArticlepeer-review


Stenotrophomonas maltophilia is an emerging global opportunistic pathogen, responsible for a wide range of human infections, including respiratory tract infections. Intrinsic multidrug resistance and propensity to form biofilms make S. maltophilia infections recalcitrant to treatment. Colistin is among the second-line options in case of difficult-to-treat S. maltophilia infections, with the advantage of being also administrable by nebulization. We investigated the potential synergism of colistin in combination with N-acetylcysteine (NAC) (a mucolytic agent with antioxidant and anti-inflammatory properties) against S. maltophilia grown in planktonic phase and biofilm. Eighteen S. maltophilia clinical isolates (comprising three isolates from cystic fibrosis (CF) and two trimethoprim-sulfamethoxazole (SXT)-resistant strains) were included. Checkerboard assays showed a synergism of colistin/NAC combinations against the strains with colistin Minimum Inhibitory Concentration (MIC) >2 µg/mL (n = 13), suggesting that NAC could antagonize the mechanisms involved in colistin resistance. Nonetheless, time–kill assays revealed that NAC might potentiate colistin activity also in case of lower colistin MICs. A dose-dependent potentiation of colistin activity by NAC was also clearly observed against S. maltophilia biofilms, also at sub-MIC concentrations. Colistin/NAC combinations, at concentrations likely achievable by topical administration, might represent a valid option for the treatment of S. maltophilia respiratory infections and should be examined further.

Original languageEnglish
Article number101
Issue number3
Publication statusPublished - Sep 1 2019


  • Biofilm
  • Colistin
  • N-acetylcysteine
  • Stenotrophomonas maltophilia

ASJC Scopus subject areas

  • Microbiology
  • Biochemistry
  • Pharmacology, Toxicology and Pharmaceutics(all)
  • Microbiology (medical)
  • Infectious Diseases
  • Pharmacology (medical)


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