Synovial Fluid Harbors Postsurgical Bacterial Biofilm

A new study suggests that prophylactic antibiotics given before joint replacement surgery are insufficient to prevent bacterial contamination.

Researchers at Thomas Jefferson University (Philadelphia, PA, USA), The US National Institutes of Health (NIH, Bethesda, MD, USA), and other institutions conducted a study to understand why joint infections persist after joint replacement surgery, despite standards of care designed to stop them. To do so, they collected clinical samples of synovial fluid that contained preoperative cefazolin in high antibiotic levels, in some cases in concentrations that far exceed the expected bactericidal levels.

The researchers then added Staphylococcus aureus bacteria to the synovial fluid samples. Not only were the bacteria not eradicated, they were able to form biofilm-like clumps and colonize model implant surfaces, such as titanium pins. The researchers found that the biofilm-like clumps were able to form because bacteria embed themselves in a protective mesh of proteins that resist penetration of antibiotics. They also found that the bacteria slowed down their growth, making them even less susceptible to the antibiotics. The study was published in the April 2015 issue of Antimicrobial Agents and Chemotherapy.

“The persistence of these bacteria in synovial fluid containing antibiotics may be one reason that joint infection is so difficult to cure,” concluded lead author Sana Dastgheyb, PhD, and colleagues. “The next step is to see how we can disperse these mega-clusters of buried bacteria. If we can provide a window for antibiotics to carry out their intended function, we can move towards a clinical model and ultimately cure joint infection.”

Antibiotic prophylaxis is standard for patients undergoing surgical procedures. But despite the wide use of antibiotics, breakthrough infections still occur at a rate of about 1%; in the setting of total joint arthroplasty, such infections can be devastating. Based on the study, the researchers suggest that current prophylactic antibiotic choices, despite high penetration into the synovial fluid, may need to be reexamined.

Related Links:
Thomas Jefferson University
US National Institutes of Health