title: Synergistic Effects of Bismuth Thiols and Various Antibiotics Against Pseudomonas aeruginosa Biofilm.
abstract: BACKGROUND
  Pseudomonas aeruginosa is an opportunistic pathogen that takes advantages of some weaknesses in the immune system to initiate an infection. Biofilms of P. aeruginosa can cause chronic opportunistic infections in immunocompromised and elderly patients. This bacterium is considered as a model organism to study antibiotic resistance as well as biofilm formation. In the biofilm structures, bacteria are protected from many harmful environmental factors such as fluctuations in the level of oxygen and nutrients, and the alterations of pH as well as sensitivity to antibiotics. Decreased permeability of biofilms is one of the important reasons of antimicrobial resistance in bacteria.
  
  
  OBJECTIVE
  In this study the anti-biofilm activity of bismuth thiols in combination with ciprofloxacin, imipenem and ceftazidime against the P. aeruginosa biofilm was investigated.
  
  
  METHODS
  Checkerboard method was used to test the susceptibility of biofilms against various antimicrobial combinations. The biofilm formation was measured by 2,3-bis (2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide (XTT) colorimetric assay. The fractional bio-film inhibitory concentration was reported for each agent.
  
  
  RESULTS
  The combination of bismuth ethanedithiol with ciprofloxacin showed synergistic inhibitory effect on the P. aeruginosa biofilm formation. The combination of bismuth ethanedithiol ciprofloxacin, ceftazidime and imipenem showed synergistic inhibitory effects on the biofilm formation. Furthermore, the combination of bismuth ethanedithiol, imipenem and ceftazidime did not show any synergistic inhibitory effect on biofilm formation.
  
  
  CONCLUSIONS
  Our studies show that using appropriate concentrations of bismuth thiols in combination with various antibiotics can act synergistically against P. aeruginosa biofilm formation.
authors.affiliation: Department of Biology, Faculty of Sciences, Alzahra University, Tehran, IR Iran.
authors.forename: Maryam
authors.initials: M
authors.lastname: Varposhti
authors.affiliation: Department of Biology, Faculty of Sciences, Alzahra University, Tehran, IR Iran.
authors.forename: Ahya
authors.initials: A
authors.lastname: Abdi Ali
authors.affiliation: Department of Biology, Faculty of Sciences, Alzahra University, Tehran, IR Iran.
authors.forename: Parisa
authors.initials: P
authors.lastname: Mohammadi
keywords: Antibacterial Agents; Biofilms; Pseudomonas aeruginosa