Proteinaceous nature of the biofilm. Top: Effect of 1mM/well sodium metaperiodate or 6U/well proteinase K on preformed biofilm. Wells show the effect of these compounds on biofilms preformed on inert polystyrene surfaces by representative ST1 isolates. Bottom: Confocal laser scanning microscopy (CLSM) images of proteinase K-treated and -untreated biofilms stained with SYTO 9. The square indicates the slice of the biofilm from which the XY image was taken. The horizontal bar indicates the location of the X plane from which the cross-section was taken. Isolate 08–008 (strong biofilm producer, agr-dysfunctional), 96/05 (moderate biofilm producer, agr-functional).