Application of a Rat Osteomyelitis Model to Comparein Vivoandin Vitrothe Antibiotic Efficacy against Bacteria with High Capacity to Form Biofilms

Abstract

A rat experimental osteomyelitis model was used to study the efficiency of antibiotics on biofilm bacteria adhered to implants in relation to the efficiency obtainedin vitro.In the osteomyelitis model, 104bacteria of the strain variant used for thein vitrostudies (a slime-producing variant ofStaphylococcus aureus) were inoculated into the rat tibia at surgery, after implanting a stainless steel canula precolonized for 12 h with this strain. After 5 weeks, a 21-day antibiotic treatment was applied (using cefuroxime, vancomycin, or tobramycin). Subsequently, implant and tibia were studied for presence of bacteria. In this osteomyelitis model, cefuroxime inhibited bone colonization and reduced the number of bacteria in metal and bone at a higher degree (P< 0.05) than vancomycin and trobramycin (the latter antibiotic did not have this reduction effect). Thein vitroassay was applied using three concentrations of each antibiotic (8, 100, and 500 μg/ml) and 6-, 24-, and 48-h biofilms. Bacterial viability was evaluated by ATP-bioluminescence after 24 h of antibiotic treatment. In thisin vitroassay, cefuroxime significantly (P< 0.05) reduced in all cases the number of viable bacteria in biofilms, tobramycin did not affect viability, and vancomycin affected viability except at the lowest concentration used (8 μg/ml, i.e., 8× the minimal bactericidal concentration of this antibiotic) when facing the oldest (48 h) biofilm. These results demonstrate the usefulness of the osteomyelitis model applied in providing evidence for a close correlation between thein vitroandin vivofindings on the effect of three antibiotics under study.