Time and concentration-dependent interaction of Pseudomonas aeruginosa with steel surfaces – A new incipient pattern emerges

The standard model of biofilm formation was established with regard to Pseudomonas aeruginosa under flow conditions, where 5 stages were noted. In the present work, the formation of P. aeruginosa biofilms was studied under static conditions on steel surfaces. It was observed that the bacteria show a distinct exploration phase on the surface, but once the solution concentration of bacteria reaches a certain stage they no longer display irreversible attachment. Very few microbes are found on the surface during this transient phase. At higher concentrations the bacteria return to the surface, and along with the few remaining irreversibly-attached microbes, thus forming a biofilm. High concentrations of bacteria in solution exposed to the surface appear to cause flatter more uniform biofilms, while those that experience lower concentrations of solution bacteria during biofilm formation appear to produce thicker and less uniform films. This transient phase of surface fouling was not observed for S. aureus , which instead showed a steady buildup of bacteria over the same time period. • P. aeruginosa bacteria presents a “transient” phase during biofilm formation under static conditions where bacteria appear to leave the surface before forming a biofilm. • This transient phase appears to be solution concentration dependent, occurring when the concentration of bacteria in solution is between approximately 80 and 200 million CFU/mL. • This transient phase was not observed for S. aureus , suggesting it is not universally applicable to all bacteria. • During the transient phase, if the static media is swapped to fresh media with no bacteria, the bacteria begin exploring the surface again before entering a new transient phase.