Influence of gentamicin and tobramycin on binary biofilm formation by co-cultures of Burkholderia cepacia and Pseudomonas aeruginosa.

The aim of this study was to investigate the stability and dynamics of binary culture biofilm formation following antibiotic treatment. Pseudo steady-state biofilm cultures of clinical strains of P. aeruginosa and B. cepacia concurrently isolated from a single CF patient were established in separate Constant Depth Film Fermenters (CDFFs). Pans, containing established biofilms, were swapped between CDFFs. Biofilms were treated either for 5 days with tobramycin (0.3 mg/ml) prior to pan-swapping, or with gentamicin (1 mg/ml) immediately following pan-swapping. In both instances stable binary biofilms were formed. In addition, fresh un-colonised surfaces added at the time of pan-swapping and exposed simultaneously to biofilm derived P. aeruginosa and B. cepacia and subjected to antibiotic challenge also established stable binary communities. Treatment of P. aeruginosa and B. cepacia with tobramycin or gentamicin, either prior to or immediately after surface colonisation had little effect on the establishment of stable binary biofilms. Such treatment also had little effect on the immigration of one organism into an established biofilm of a second organism.