Bacteriophage Multiplication in Escherichia coli and Pseudomonas aeruginosa Mixed Biofilm Communities

Abstract

The use of single species bacteriophage infection to control bacterial populations in mixed, planktonic cultures has met limited success. Since many chronic infections occur as mixed species biofilms we investigated the effect of double species phage infection in both mixed species planktonic culture and biofilms. This study reports the effect of Escherichia coli bacteriophage A W60 and Pseudomonas aeruginosa bacteriophage PB-1 infection on the viability of mixed species biofilm and planktonic cultures. In both mixed species planktonic and biofilm communities, E. coli and P. aeruginosa maintained stable cell populations in the presence of their phage. Both E. coli and P. aeruginosa developed phage resistance in planktonic culture, however, reduced resistance was observed in biofilm communities. Increased phage titers and reduced resistance in biofilms suggests phage are capable of replicating on susceptible cells in biofilms. Electron Microscopy of biofilm supernatants revealed bacteriophage particles enmeshed in extracellular polymeric substance (BPS). Treatment of biofilm supernatants with Tween-20 resulted in an increase in infectivity which suggests biofilms' BPS can act as a natural reservoir for phage and affords protection from phage infection. The results of this study demonstrate that the use of double species phage infection did not result in an additive bacteriocidal effect in either mixed planktonic or biofilm communities, but may be effective in preventing spread from established biofilms.