title: Antibiotic susceptabilities of Pseudomonas aeruginosa isolates derived from patients with cystic fibrosis under aerobic, anaerobic, and biofilm conditions.
abstract: Recent studies have determined that Pseudomonas aeruginosa can live in a biofilm mode within hypoxic mucus in the airways of patients with cystic fibrosis (CF). P. aeruginosa grown under anaerobic and biofilm conditions may better approximate in vivo growth conditions in the CF airways, and combination antibiotic susceptibility testing of anaerobically and biofilm-grown isolates may be more relevant than traditional susceptibility testing under planktonic aerobic conditions. We tested 16 multidrug-resistant isolates of P. aeruginosa derived from CF patients using multiple combination bactericidal testing to compare the efficacies of double and triple antibiotic combinations against the isolates grown under traditional aerobic planktonic conditions, in planktonic anaerobic conditions, and in biofilm mode. Both anaerobically grown and biofilm-grown bacteria were significantly less susceptible (P < 0.01) to single and combination antibiotics than corresponding aerobic planktonically grown isolates. Furthermore, the antibiotic combinations that were bactericidal under anaerobic conditions were often different from those that were bactericidal against the same organisms grown as biofilms. The most effective combinations under all conditions were colistin (tested at concentrations suitable for nebulization) either alone or in combination with tobramycin (10 microg ml(-1)), followed by meropenem combined with tobramycin or ciprofloxacin. The findings of this study illustrate that antibiotic sensitivities are dependent on culture conditions and highlight the complexities of choosing appropriate combination therapy for multidrug-resistant P. aeruginosa in the CF lung.
authors.affiliation: Department of Infectious Diseases and Immunology, University of Sydney, Sydney, Australia.
authors.forename: Dominic
authors.initials: D
authors.lastname: Hill
authors.forename: Barbara
authors.initials: B
authors.lastname: Rose
authors.forename: Aniko
authors.initials: A
authors.lastname: Pajkos
authors.forename: Michael
authors.initials: M
authors.lastname: Robinson
authors.forename: Peter
authors.initials: P
authors.lastname: Bye
authors.forename: Scott
authors.initials: S
authors.lastname: Bell
authors.forename: Mark
authors.initials: M
authors.lastname: Elkins
authors.forename: Barbara
authors.initials: B
authors.lastname: Thompson
authors.forename: Colin
authors.initials: C
authors.lastname: Macleod
authors.forename: Shawn D
authors.initials: SD
authors.lastname: Aaron
authors.forename: Colin
authors.initials: C
authors.lastname: Harbour
mesh_terms: D000332:Aerobiosis; D000693:Anaerobiosis; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001431:Bacteriological Techniques; D018441:Biofilms / Q000254:growth & development*; D003550:Cystic Fibrosis / Q000382:microbiology*; D024901:Drug Resistance, Multiple, Bacterial; D004359:Drug Therapy, Combination; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D011552:Pseudomonas Infections / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000254:growth & development* / Q000302:isolation & purification; D013183:Sputum / Q000382:microbiology
chemical_list: D000900:Anti-Bacterial Agents