Kinetics and morphology of polymicrobial biofilm formation on polypropylene mesh

We examined the ability of three clinical bacterial isolates to form mixed biofilms on surgical polypropylene mesh (PPM) in vitro . The three strains – S taphylococcus aureus , E nterococcus faecalis, and E nterobacter cloacae – were isolated from a patient with an infected PPM. S taphylococcus aureus and E . faecalis (alone and in combination) were inoculated into culture containing squares of PPM and allowed to attach and propagate into mature biofilms. E nterococcus faecalis initially attached to the mesh in greater numbers; however, 7 days postinoculation, there were more S . aureus cells attached, indicating that in vitro S . aureus is the out‐competing species. All three isolates were then co‐cultured to form mature biofilms on mesh, and the biofilms were examined by confocal microscopy using both Live/Dead staining and fluorescent in situ hybridization ( FISH ). Imaging revealed a dense biofilm structure with interstitial voids and channels; rods and cocci were interspersed throughout the biofilm, indicating bacterial coexistence in close proximity. FISH revealed staphylococci and enterococci adjacent to each other and also to the E nterobacter , distinguishable by its rod morphology. These studies show that different species can co‐operatively form mature biofilms on mesh but that the relative abundance of a species within the biofilm may vary over time.