Resistance to Tobramycin in Pseudomonas aeruginosa PA14 and PA14 ΔpelB Co-culture Biofilm through Antibiotic Sequestering

Biofilms consist of complex communities of bacteria, spatially structured with functionally dependent interactions. The extracellular polymeric substances in biofilms, consisting of polysaccharides such as Pel, have been shown to enhance resistance of these communities towards aminoglycoside antibiotics. The ability of Pel, produced by the wild type, to confer resistance for communities of different wt to pel B mutant ratios towards tobramycin through a gradient or threshold mechanism was examined by the co-culturing of Pseudomonas aeruginosa PA14 wild type and PA14 Δ pel B mutant. The PA14 wild type and PA14 pel B mutant were cultured independently and then co-cultured in ratios of 3:1, 1:1, and 1:3. PA14 wild type produced more biofilm than the PA14 pel B mutant, with an increasing amount produced as the ratio of PA14 wild-type to PA14 pel B mutant increased. The co-culture ratios were not maintained, while the average colony counts were significantly higher for pel B mutants compared to PA14 wild type. Further studies with improved protocols to optimize the disruption of biofilms are needed to determine the survivability ratios after exposure of the biofilm to tobramycin.