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Δευτέρα 19 Νοεμβρίου 2018

In-vivo gentamicin susceptibility test for prevention of bacterial biofilms in bone tissue and on implants [Susceptibility]

Objectives: To set up an in-vivo gentamicin susceptibility test for biofilm prevention in bone tissue and on implants.

Methods: Twenty-five pigs were allocated to six groups. Group A (n=6) was inoculated with saline. Groups B (n=6), C (n=3), D (n=3), E (n=3) and F (n=4) were inoculated with 10 μL saline containing 104 CFU of Staphylococcus aureus. Different concentrations based on the minimal inhibitory concentrations (MIC) of gentamicin to the specific strain were added to the 10 μL inoculum of Groups C (160xMIC), D (1,600xMIC), E (16,000xMIC) and F (160,000xMIC). The inoculums were injected into a pre-drilled tibial implant cavity followed by insertion of a steel implant (2 x 15 mm). The pigs were euthanized after five days. In-vitro, all the used doses were found bacteriostatic after up to 6 hours.

Results: All implant cavities of pigs inoculated with bacteria and bacteria + 160xMIC or 1,600xMIC were positive for S. aureus. In each of the Groups E (16,000xMIC) and F (160,000xMIC) 2/3 and 1/4 of the implant cavities were S. aureus positive, respectively. By grouping Groups C + D (<10,000xMIC) and Groups E + F (>10,000xMIC) a significant decrease of implant attached bacteria was only seen between the high MIC value group and Group B. Histologically, it was demonstrated that 1,600, 16,000 and 160,000 x MIC resulted in a peri-implant tissue reaction comparable to saline inoculated animals.

Conclusion: In-vivo, the antimicrobial tolerance of the inoculated planktonic bacteria was increased by in-vivo specific factors of acute inflammation. This resulted in bacterial aggregation and biofilm formation which further increased the gentamicin tolerance. Thus, susceptibility patterns in-vitro might not reflect the actual in-vivo susceptibility locally within a developing infectious area.



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