The leading cause of morbidity and mortality in cystic fibrosis (CF) contin
ues to be lung infections with Pseudomonas aeruginosa biofilms. Co-coloniza
tion of the lungs with P. aeruginosa and Burkholderia cepacia can result in
more severe pulmonary disease than P. aeruginosa alone. The interactions b
etween P. aeruginosa biofilms and B. cepacia are not yet understood; one po
ssible association being that mixed species biofilm formation may be part o
f the interspecies relationship. Using the Calgary Biofilm Device (CBD), me
mbers of all genomovars of the B. cepacia complex were shown to form biofil
ms, including those isolated from CF lungs. Mixed species biofilm formation
between CF isolates of P. aeruginosa and B. cepacia was readily achieved u
sing the CBD. Oxidation-fermentation lactose agar was adapted as a differen
tial agar to monitor mixed biofilm composition. Scanning electron micrograp
hs of the biofilms demonstrated that both species readily integrated in clo
se association in the biofilm structure. Pseudomonas aeruginosa laboratory
strain PAO1, however, inhibited mixed biofilm formation of both CF isolates
and environmental strains of the B. cepacia complex. Characterization of t
he soluble inhibitor suggested pyocyanin as the active compound.