title: Repetitive methylene blue-mediated photoantimicrobial chemotherapy changes the susceptibility and expression of the outer membrane proteins of Pseudomonas aeruginosa.
abstract: BACKGROUND
  Since bacterial multidrug efflux pumps mediate intracellular photosensitizer methylene blue, a change in the expression alters the susceptibility to photoantimicrobial chemotherapy (PACT) of Pseudomonas aeruginosa, which may occur following repetitive sublethal challenges.
  
  
  METHODS
  We performed 10 consecutive, methylene blue-mediated PACT on one antibiotic-sensitive strain and three antibiotic-resistant strains of P. aeruginosa. Following each therapy, the surviving bacteria were collected for subsequent PACT. The susceptibility was compared for the pre- and the post-treated strains following repetitive PACT. To explore the existence of efflux pumps, one of the inhibitors, namely Phe-Arg β-naphthylamide dihydrochloride (PAβN 25 μg/ml), was added. Profiles of outer membrane proteins were obtained for the pre-treated and the post-treated strains.
  
  
  RESULTS
  The susceptibility of PACT did not correlate with the antibiotic sensitivity. Following ten PACT, there was no significant change in susceptibility for three tested strains, except for one antibiotic-resistant strain, for which the 10th generation became less susceptible than the original one. With 2-D electrophoresis, a change in the expression of outer membrane proteins was observed. PAβN successfully increased the phototoxicity in all tested strains, especially the less PACT-susceptible 10th generation of the antibiotic-resistant strain.
  
  
  CONCLUSIONS
  Following repetitive challenges, PACT had a consistent antimicrobial effect on three strains; however, one antibiotic-resistant strain, which was the most vulnerable to PACT, became more resistant after consecutive challenges. In addition, the post-PACT strain had different expression of outer membrane proteins, providing further evidence view that repetitive PACT with methylene blue could change the expression of efflux pumps.
authors.affiliation: Department of Ophthalmology, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan, ROC.
authors.forename: Min-Hsiu
authors.initials: MH
authors.lastname: Shih
authors.forename: Fu-Chin
authors.initials: FC
authors.lastname: Huang
mesh_terms: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D024881:Drug Resistance, Bacterial / Q000187:drug effects* / Q000502:physiology / Q000528:radiation effects; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D008751:Methylene Blue / Q000494:pharmacology*; D010778:Photochemotherapy / Q000379:methods; D017319:Photosensitizing Agents / Q000494:pharmacology; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000378:metabolism* / Q000528:radiation effects
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D017319:Photosensitizing Agents; D008751:Methylene Blue
keywords: CFU; Efflux pump; MB; MEP; Methylene blue; OMP; Outer membrane protein; PACT; PAβN; Phe-Arg β-naphthylamide dihydrochloride; Phenothiazinium; Photoantimicrobial chemotherapy; Pseudomonas aeruginosa; colony-forming unit; methylene blue; multidrug efflux pump; outer membrane protein; photoantimicrobial chemotherapy