Co-culture Inhibition through Local Delivery with Chitosan Sponge

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Authors: Smith J, Parker A, Jennings J, Courtney H, Beenken K, Smeltzer M, Haggard W.
The University of Memphis, Memphis, TN

Title: Co-culture Inhibition through Local Delivery with Chitosan Sponge

Background: Polymicrobial infection prevention is critical to managing open, contaminated musculoskeletal wounds. Our strategy is to use local antibiotic delivery from a dual-loaded chitosan sponge (CS) to reduce polymicrobial contamination.

Hypothesis/Purpose: (1) What are the release kinetics and eluate antibiotic activity effects of dual-antibiotic delivery from a CS and (2) does it effectively reduce polymicrobial infection in vivo?

Methods: CS (n=3) were loaded with 5mg/ml of amikacin, vancomycin, or a combination thereof (10mg/ml total). Elution samples were taken at 1, 3, 6, 12, 24, 48 and 72 hour time points and antibiotic concentrations were quantified. The samples' activity was evaluated by introducing them (in a 1:10 dilution, n=3) to S. aureus, P. aeruginosa, or a co-culture thereof. After incubation overnight, the sample's optical density was measured to indicate bacterial growth (+) or inhibition (‒). For the in vivo study, 1cm catheter sections were implanted subcutaneously in the flanks of NIH Swiss mice and inoculated with S. aureus, P. aeruginosa, or a co-culture thereof. Concurrently, a CS loaded with amikacin, vancomycin, or a combination thereof was implanted adjacent to the catheter. After 24 and 48 hours the catheters were harvested and the therapeutic response was assessed from the total number of viable bacteria colonizing each catheter.

Results: Antibiotic elution results showed an initial burst and extended release profile for the combination antibiotics (Figure 1A), similar to individually loaded antibiotic release profiles. Antibiotic elution samples with sufficiently high concentrations were inhibitory of their respective Gram-positive or negative species (combination elution in Figure 1B). Preliminary results from the infected mouse catheter model indicated that the combination loaded sponges cleared the infection from all catheters after 24 hours. At 48 hours, the in vivo study revealed the presence of some viable bacterial colonies.

Discussion: This study demonstrated that dual-antibiotic loaded CS have beneficial release kinetics of antibiotics active against a bacterial co-culture. The polymicrobial mouse model produced promising results after 24 hours, although viable bacterial colonies seen after 48 hours may be due to a number of possible causes.

Conclusion: The dual-antibiotic loaded CS has beneficial in vitro properties and initial results in a polymicrobial infection prevention mouse catheter model warrant further investigation.

Co-culture Inhibition through Local Delivery with Chitosan Sponge