Green and red fluorescent protein vectors for use in biofilm studies of the intrinsically resistant Burkholderia cepacia complex.

Cystic fibrosis isolates of the Burkholderia cepacia complex (BCC) have demonstrated a propensity to associate intimately with Pseudomonas aeruginosa in mixed community biofilms, which may impact on their overall pathogenicity during infection of the lungs in cystic fibrosis. Here, we describe the construction and use of novel green and red fluorescent protein expression vectors suitable for labeling biofilm cells of multi-resistant clinical isolates of the BCC for microscopic analysis of both single species biofilms and mixed community associations with P. aeruginosa. Antimicrobial susceptibility testing established that tetracycline and/or trimethoprim were suitable selective agents for widespread use in BCC. The green and red fluorescent protein genes, driven by constitutively active promoters, were cloned into two mobilizable plasmids pBBR1MCS-3 and pBBR1Tp, carrying tetracycline and trimethoprim resistance cassettes, respectively. The fluorescence of transformed BCC and P. aeruginosa planktonic cells was detectable using fluorescence microscopy and/or fluorometry. The plasmids were stable in the absence of selection for at least 3 days in planktonic and biofilm cultures, and fluorescence was still visible in a 4-day glass coverslip flow cell biofilm. The plasmids functioned well to distinguish the two species in a mixed community biofilm, with no indications of plasmid transfer between species or cross-talk of the fluorescent signals. These vectors represent the first green and red fluorescent vectors to be constructed and analyzed specifically for wide spread use in BCC and P. aeruginosa single and mixed biofilm cultures.