Cobalt–Chromium Alloy Has Superior Antibacterial Effect Than Titanium Alloy: In Vitro and In Vivo Studies

In vitro and in vivo laboratory studies. OBJECTIVE. This study aimed to compare bacterial survival on titanium alloy (Ti) and cobalt–chromium alloy (CC) using in vitro and in vivo experiments. SUMMARY OF BACKGROUND DATA. Spinal implants are frequently manufactured from Ti and CC. These foreign materials are thought to be susceptible to biofilm formation that contributes to the development of surgical site infections. Certain metals (i.e., silver, cobalt) are known to have antibacterial properties. METHODS. In the in vitro study, discs made of Ti or CC were incubated with one of two common bacteria: Staphylococcus aureus (S. aureus) and Propionibacterium acnes (P. acnes). After incubation, discs were assessed to determine the number of viable bacterial cells. In the in vivo study, the discs that were made of CC or Ti were implanted into the subcutaneous layer of BALB/c mice. After skin closure, a suspension including either S. aureus or P. acnes was directly inoculated on the implanted discs. The discs were retrieved and analyzed to determine the number of viable bacteria at 0.5, 1, and 3 days after inoculation. RESULTS. The number of viable S. aureus cultured from the CC discs was 0.9 ± 0.2 × 10(3) CFU/disc, which was significantly lower than the cultured Ti discs (114.8 ± 18.3 × 10(3) CFU/disc). Moreover, a significantly lower mean number of P. acnes were cultured with CC (1.9 ± 1.2 × 10(3) CFU/disc) compared with the Ti (180.0 ± 72.1 × 10(3) CFU/disc). The in vivo infection model testing against S. aureus or P. acnes showed a significantly lower number of viable S. aureus or P. acnes on CC discs than Ti discs. The result was seen at all measured time points. CONCLUSION. CC suppressed S. aureus and P. acnes proliferation compared with Ti in vitro and in an in vivo infection model. Level of Evidence: N/A