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Kinetics and morphology of polymicrobial biofilm formation on polypropylene mesh
Paul Stoodley1, Sandeep Sidhu, Laura Nistico
1National Centre for Advanced Tribology, School of Engineering Sciences, University of Southampton, Southampton, UK.
Abstract:
We examined the ability of three clinical bacterial isolates to form mixed biofilms on surgical polypropylene mesh (PPM) in vitro. The three strains--Staphylococcus aureus, Enterococcus faecalis, and Enterobacter cloacae--were isolated from a patient with an infected PPM. Staphylococcus 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. Enterococcus 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 Enterobacter, 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.
Insights
Clinical bacterial isolates form mixed biofilms on surgical polypropylene mesh (PPM). Staphylococcus aureus out-competes other species over time, yet all coexist in a complex biofilm structure.
Area of Science:
- Microbiology
- Biomaterials Science
- Infectious Diseases
Background:
- Surgical mesh infections are a significant clinical challenge.
- Understanding polymicrobial biofilm formation on implants is crucial for treatment.
- Polypropylene mesh (PPM) is commonly used in surgical procedures.
Purpose of the Study:
- To investigate the in vitro biofilm formation of three clinical bacterial isolates on PPM.
- To characterize the spatial organization and coexistence of different bacterial species within the biofilm.
- To assess the competitive dynamics between bacterial species during biofilm development on PPM.
Main Methods:
- In vitro culture of Staphylococcus aureus, Enterococcus faecalis, and Enterobacter cloacae on PPM.
- Confocal laser scanning microscopy for biofilm imaging.
- Live/Dead staining and fluorescent in situ hybridization (FISH) for species identification and spatial distribution.
Main Results:
- Mixed bacterial biofilms readily formed on PPM, exhibiting complex structures with voids and channels.
- Initially, Enterococcus faecalis adhered in higher numbers, but Staphylococcus aureus became dominant after 7 days.
- FISH confirmed the close proximity and coexistence of S. aureus, E. faecalis, and E. cloacae within the mature biofilm.
Conclusions:
- Multiple bacterial species can cooperatively form mature biofilms on surgical polypropylene mesh.
- Bacterial species coexist within the biofilm, despite potential competitive interactions.
- The relative abundance of bacterial species within the biofilm can change dynamically over time.
