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Novel in vitro model for assessing susceptibility of synthetic hernia repair meshes to Staphylococcus aureus infection using green fluorescent protein-labeled bacteria and modern imaging techniques.

BACKGROUND
Mesh infection complicating hernia repair is a major cause of patient morbidity and results in substantial healthcare expenditures. The various constructs of prosthetic mesh may alter the ability of bacteria to attach and form a biofilm. Few data exist evaluating biofilm formation. Using the Maestro in-Vivo Imaging System (CRi, Inc., Woburn, MA) to detect green fluorescent protein (GFP)-expressing Staphylococcus aureus, we studied the ability of synthetic mesh to withstand bacterial biofilm formation in an in vitro model.


METHODS
We included four meshes: Polypropylene (PP), polypropylene/expanded PTFE (PX), compressed PTFE (cPTFE), and polyester/polyethylene glycol and collagen hydrogel (PE). Five samples of each mesh were exposed to GFP-expressing S. aureus for 18 h at 37°C. Next, green fluorescence was measured using the Maestro Imaging System, with the results expressed in relative fluorescence units (RFU), subtracting the fluorescence of uninfected mesh (control). Each mesh subsequently underwent sonication and quantitative culture of the released bacteria, with the results expressed in colony-forming units (CFU). Analysis of variance was performed to compare the mean values for the different meshes.


RESULTS
There was a statistically significant difference in bacterial fluorescence for the four meshes: PE (49.9 ± 25.5 [standard deviation] RFU), PX (30.8 ± 9.4 RFU), cPTFE (10.1 ± 4.0 RFU), and PP (5.8 ± 7.5 RFU)(p = 0.001). Bacterial counts also were significantly different: PE (2.2 × 10(8) CFU), PX (8.6 × 10(7) CFU), cPTFE (3.7 × 10(7) CFU), and PP (9.1 × 10(7) CFU)(p < 0.001).


CONCLUSION
Using novel imaging technology, this study documented significantly different amounts of S. aureus biofilm formation and proliferation on different mesh constructs, with good agreement between imaging and culture results. A multifilament woven mesh (PE) had the highest degree of biofilm formation. These findings are being evaluated in a clinical infection model.