antibacterial and antibiofilm activities of diclofenac against levofloxacin-resistant stenotrophomonas maltophilia isolates; emphasizing repurposing of diclofenac

Background and objectives: stenotrophomonas maltophilia is an opportunistic pathogen causing nosocomial infections. diclofenac is an anti-inflammatory drug that is considered a non-antibiotic drug. this study assessed the antibacterial and antibiofilm effects of diclofenac and levofloxacin/diclofenac combination against levofloxacin resistant isolates.materials and methods: minimum inhibitory concentration was determined using broth microdilution method for levofloxacin, diclofenac, and levofloxacin/diclofenac combination. biofilm forming capacity and biofilm inhibition assay were determined. relative gene expression was measured for efflux pump genes; smeb, and smef genes and biofilm related genes rmla, spgm, and rpff without and with diclofenac and the combination.results: diclofenac demonstrated mic of 1 mg/ml. the combination-with 1/2 mic diclofenac- showed synergism where levofloxacin mic undergone 16-32 fold decrease. all the isolates that overexpressed smeb and smef showed a significant decrease in gene expression in presence of diclofenac or the combination. the mean percentage inhibition of biofilm formation with diclofenac and the combination was 40.59% and 46.49%, respectively. this agreed with biofilm related genes expression investigations.conclusion: diclofenac showed an antibacterial effect against stenotrophomonas maltophilia. the combination showed in-vitro synergism, significant reduction in biofilm formation and in the relative level of gene expression. furthermore, it can potentiate the levofloxacin activity or revert its resistance.