In VivoGentamicin Susceptibility Test for Prevention of Bacterial Biofilms in Bone Tissue and on Implants
ABSTRACTThe objective of this study was to set up anin vivogentamicin susceptibility test for biofilm prevention in bone tissue and on implants. Twenty-five pigs were allocated to six groups. Pigs in group A (n= 6) were inoculated with saline. Pigs in groups B (n= 6), C (n= 3), D (n= 3), E (n= 3), and F (n= 4) were inoculated with 10 μl saline containing 104CFU ofStaphylococcus aureus. Different concentrations based on the MIC of gentamicin for the specific strain were added to the 10-μl inoculum for groups C (160× MIC), D (1,600× MIC), E (16,000× MIC), and F (160,000× MIC). The inocula were injected into a predrilled tibial implant cavity, followed by insertion of a steel implant (2 by 15 mm). The pigs were euthanized after 5 days.In vitro, all the doses used were found to be bactericidal after up to 6 h. All implant cavities of pigs inoculated with bacteria and bacteria plus 160× MIC or 1,600× MIC of gentamicin were positive forS. aureus. In animals in each of groups E (16,000× MIC) and F (160,000× MIC), 2/3 and 1/4 of the implant cavities wereS. aureuspositive, respectively. By grouping groups C and D (<10,000× MIC) and groups E and F (>10,000× MIC), a significant decrease in the number of implant-attached bacteria was seen only between the high-MIC-value group and group B. Histologically, it was demonstrated that 1,600×, 16,000×, and 160,000× MIC resulted in a peri-implant tissue reaction comparable to that in saline-inoculated animals.In vivo, the antimicrobial tolerance of the inoculated planktonic bacteria was increased byin vivo-specific factors of acute inflammation. This resulted in bacterial aggregation and biofilm formation, which further increased the gentamicin tolerance. Thus, susceptibility patternsin vitromight not reflect the actualin vivosusceptibility locally within a developing infectious area.