Factors controlling bacterial attachment and biofilm formation on medium-chain-length polyhydroxyalkanoates (mcl-PHAs)

Polyhydroxyalkanoate (PHA) is a versatile class of biodegradable and biocompatible biopolyesters accumulated by many bacteria as intracellular carbon storage compound. The largest subclass consists of medium-chain-length (mcl) PHA which has a large potential in medical applications where flexible or elastomeric materials are required. Different extraction and purification methods for mcl-PHA are known to result in variations of polymer purities. In this study it was assessed whether this difference in quality may increase risk of failure of the implant material by enhanced colonization by Gram-negative and Gram-positive model pathogens (Staphylococcus aureus and Escherichia coli curli). Two types of mcl-PHA copolymers, poly(3-hydroxyoctanoate) (PHO) and the less known poly(3-hydroxyundecanoate) (PHUA), were evaluated for an impact of monomeric unit composition and degree of polymer purity on colonization by the model pathogens. It was found that film formation by bacteria on purified PHO and PHUA coatings was lower or similar to the one observed for polystyrene controls. The presence of proteins and lipopolysaccharide impurities originating from biotechnological production contributed to an increase in biofilm development probably by triggering the attachment of bacterial cells. In addition it was found that the model strains used differed significantly in colonizing the surfaces. For both types of mcl-PHAs E. coli curli was always a better biofilm former than S. aureus, which could be explained by the presence of curli (protein) fibers and a less hydrophilic cell wall.