Abstract
Each year there are approximately 2.9 million joint replacement surgeries performed worldwide. Great efforts have been made to reduce infection rates in these replacements in the past and yet these rates have not decreased in the past 20 years. These infections are often caused by the formation of biofilms on the surface of the implant by skin bacteria that are implanted at the time of surgery. The S-adenosylmethionine (SAM) cycle has important roles in bacterial biofilm formation. Methylthioadenosine-nucleosidase (MTAN) is an important component in this cycle.
The Ferrier Institute at Victoria University have synthesized approximately thirty compounds which have been shown to inhibit the MTAN enzyme. Testing of ten organisms of each Staphylococcus aureus and Staphylococcus epidermidis all isolated from infected joint prosthesis was undertaken to determine the strongest biofilm formers. Over 90% of organisms that infect prosthetic joint replacements are found to be S. epidermidis or S. aureus, which is why these organisms were used as models. The isolates in combination with MTAN inhibitors (MTANi) were screened using a crystal violet assay to determine biofilm formation. An optical density reading was used to determine bacterial growth. Minimum inhibitory concentration (MIC) testing on four clinically relevant antibiotics was performed using a doubling dilution broth culture method. The effect of these antibiotics on the efficacy of the lead inhibitor was analysed using an optical density growth assay and static biofilm assay. Fluorescent images of the biofilms were produced using the LIVE/DEAD® BacLight™ bacterial viability method of staining.
In testing of the strongest biofilm forming isolates, a lead compound (MTANi18) has been identified that inhibited biofilm formation in both S. aureus and S. epidermidis. Some effects on growth were noted at high concentrations of the MTAN inhibitor. It has been observed that MTANi18 affects the action of four clinically relevant antibiotics, in an agonistic manner. Further testing is required to determine the extent of this phenomenon.
These findings have important implications in the potential therapeutic uses of the MTAN inhibitors.