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.

https://ift.tt/2zfPDk8