A comparison of Staphylococcus aureus biofilm formation on cobalt-chrome and titanium-alloy spinal implants

• The use of cobalt chrome (CoCr) implants in spinal surgery has become increasingly popular.
• Biofilm formation on CoCr and titanium-alloy implants has not been studied.
• After incubation, optical density and colony forming units were calculated.
• CoCr had a higher proclivity towards biofilm formation compared to titanium-alloy.

The use of cobalt chrome (CoCr) implants in spinal surgery has become increasingly popular. However, there have been no studies specifically comparing biofilm formation on CoCr with that of titanium-alloy spinal implants. The objective of this study was to compare the difference in propensity for biofilm formation between these two materials, as it specifically relates to spinal rods. Staphylococcus aureus subsp. Aureus (ATCC 6538) were incubated with two different types of spinal rods composed of either CoCr or titanium-alloy. The spinal rods were then subject to a trypsin wash to allow for isolation of the colonized organism and associated biofilms. The associated optical density values (OD) from the bacterial isolates were obtained and the bacterial solutions were plated on brain-heart infusion agar plates and the resultant colony-forming units (CFU) were counted. The OD values for the titanium-alloy rods were 1.105 ± 0.096 nm (mean ± SD) and 1.040 ± 0.026 nm at 48 hours and 96 hours, respectively. In contrast, the OD values for the CoCr rods were 1.332 ± 0.161 nm and 1.115 ± 0.207 nm at 48 and 96 hours, respectively (p < 0.05). The CFU values were 1481 ± 417/100 mm2 and 745 ± 159/100 mm2 at 48 and 96 hours, respectively for the titanium-alloy group. These values were significantly lower than the CFU values obtained from the CoCr group which were 2721 ± 605/100 mm2 and 928 ± 88/100 mm2 (p < 0.001) at both 48 and 96 hours respectively. Our findings, evaluating both the OD and CFU values, indicate that implants composed of CoCr had a higher proclivity towards biofilm formation compared to titanium-alloy implants.