Reduction in exopolysaccharide viscosity as an aid to bacteriophage penetration through Pseudomonas aeruginosa biofilms

To cause an infection, bacteriophages must penetrate the alginate exopolysa ccharide of Pseudomonas aeruginosa to reach the bacterial surface. Despite a lack of intrinsic motility, phage were shown to diffuse through alginate gels at alginate concentrations up to 8% (wt/vol) and to bring about a 2-lo g reduction in the cell numbers in 20-day-old biofilms of P, aeruginosa, Th e inability of alginate to act as a more effective diffusional barrier sugg ests that phage may cause a reduction in the viscosity of the exopolysaccha ride, Samples (n = 5) of commercial alginate and purified cystic fibrosis ( CF) alginate were incubated with 2 x 10(8) purified phage per mi for 24 h a t 37 degreesC. After incubation the samples and controls were subjected to theological analysis with a Carrimed controlled stress rheometer, The visco sities of phage-treated samples were reduced by up to 40% compared to those of controls incubated in the absence of phage, The experiment was repeated by using phage concentrations of 10(10) and 10(12) phage per mi and sample s taken for analysis at intervals up to 4 h. The results indicated that the re was a time- and concentration-dependent reduction in viscosity of up to 40% compared to the viscosities of the controls. Commercial and purified CF alginate samples, both phage treated and untreated, were subjected to gel filtration chromatography by using Sephacryl High Resolution S-400 medium i n order to obtain evidence of degradation. The results demonstrated that al ginate treated with phage had a lower molecular weight than untreated algin ate. The data suggest that bacteriophage migration through P. aeruginosa bi ofilms may be facilitated by a reduction in alginate viscosity brought abou t by enzymic degradation and that the source of the enzyme may be the bacte rial host itself.