Impact of Growth Conditions on Biofilm Formation by Model Gram- Negative and Gram-Positive Bacterial Strains

Present-day medical microbiology faces the risks of biofilm-related infections. These are much more resistant to routinely applied antibacterial preparations, and are often the cause of recurrent infections. The search of novel anti-fouling preparations puts forward the elaboration of a reliable complex approach for selecting and estimating the successful agent. As a first step, screening procedures should include a fast methodology, and the crystal violet assay is widely applied for semi-quantitative estimation of biofilm biomass. However, the species- and strain-peculiar mechanisms of biofilm formation require optimisation of the experimental protocols with regards to the individual demands of model strains. This study aims to characterise the biofilm-forming behavior of a set of model Gram-positive and Gram-negative strains. The Gram-positive strains included in the experiments were Staphylococcus aureus ATCC 29213 and Bacillus subtilis 168. Gram-negative strains were Pseudomonas aeruginosa PAO1 and six Escherichia coli K-12 strains. The tested variables were growth medium, time of cultivation and growth temperature. Notably, these variables have different, sometimes even opposite effects on planktonic growth and biofilm development. The results provide information needed for the proper design of further screening experiments on these strains, for novel substances with putative anti-biofilm activities.