Effects of positively charged- and plasma-treated surface on biofilm growth of various subtypes of Staphylococcus aureus and Pseudomonas aeruginosa

Biofilm study is important because approximately 65% to 80% of all infections are caused by biofilms and resistance against antibiotics is up to ten times more when bacteria are in biofilms. Biofilm models using in vitro model systems offer affordable and fast results albeit several limitations to mimic physiological environment for optimum microbial growth. This study aims to address some of the limitations when growing mixed cultures of ATCC and clinical isolates of Staphylococcus aureus and Pseudomonas aeruginosa – the two main pathogens in osteomyelitis. Variables were tested in this experiment: (i) using conditioned surface for biofilm attachment (plasma and poly-LLysine, PLL) and (ii) with different incubation times. Biofilm biomass was quantified by determining the crystal violet absorbance (A570). Results showed that at 16 h incubation, S. aureus biofilms did not grow well on PLL-treated plates. In addition, the biofilm biomass of S. aureus strains was reduced at 24 h incubation in all treated groups, except for the strong biofilm producers in untreated plates. Similarly, biofilm biomass of P. aeruginosa strains was also higher at 16 h than 24 h incubation. Treating plate surfaces with plasma and PLL did not have any effect on P. aeruginosa strains. The study concludes that PLL and plasma-treated plates have no influence in biofilm growth for both S. aureus and P. aeruginosa at 24 h incubation. However, at 16 h incubation, PLL may have inhibited the biofilm growth of S. aureus. The optimum incubation time to grow biofilms in vitro for S. aureus is between 16 and 24 h while P. aeruginosa is best grown at 16 h incubation. Although other factors may influence the bacterial growth in vitro, this study demonstrated that the use of brain heart infusion for various subtypes of bacteria is favorable for antimicrobial study of polymicrobial biofilms