Studying formation of Pseudomonas aeruginosa biofilms grown under different cultivation conditions
The purpose of the present study is to assess how cultivation conditions influence growth and formation of Pseudomonas aeruginosa biofilms. The topic is of great importance due to high incidence of P. aeruginosa-caused infections and P. aeruginosa resistance associated with its ability to form biofilms. The paper analyzes factors that influence biofilm formation, i.e.: growth phase used for inoculation (log, stationary), volume of the growth medium (0.2 and 1.0 ml) and concentration of nutrients (liquid nutrient media diluted to concentrations of 50; 25; 12.5 and 6%) in the cultivation volume. As the research demonstrates, all these factors influence biofilm formation; and a P. aeruginosa growth phase before inoculation is a determining factor in the biofilm formation. When P. aeruginosa is inoculated at a stationary phase, biofilm formation shows non-linear dependence on concentration of nutrients and on their total amount in the cultivation volume. The linear dependence of biofilm formation on concentration of nutrients in the culture medium is more pronounced, when P. aeruginosa is inoculated at a log phase. The study shows that lower concentrations of nutrient media components lead to more noticeable differences in biofilm formation, and such differences are statistically significant. Two-fold dilution of the liquid nutrient medium does not affect the intensity of biofilm formation; however, a 4 to 8-fold decrease in concentration of nutrients in 0.2 ml of cultivation volume inhibited the biofilms formation. In 1.0 ml of the culture medium, the biofilm forms evenly, and in 0.2 ml of 4-8-fold dilution of nutrient medium it grows slower. The slow growth rate is statistically significant. The cultivation volume is also of great importance. For example, cultures grown in 0.2 ml of nutrient medium at different concentrations of nutrients formed fewer biofilms than microorganisms cultivated in 1.0 ml. At the same time, when inoculating P aeruginosa both at log and stationary growth phases, biofilm formation is more pronounced in wells containing more cultivation volume.