Novel antibiotic coating shows potential for use on surgical implants

An experimental coating that uses a cationic steroid antibiotic may remain active against bacteria much longer than current drug-eluting implants.

A novel antimicrobial device coating that contains a cationic steroid antibiotic showed efficacy against high levels of Staphylococcus aureus and Escherichia coli bacteria in an experimental in vitro study.

The coating used in the study, called Ceracide (Ceragenix Pharmaceuticals Inc.), prevented bacterial colonization on titanium surfaces and also eliminated bacteria in surrounding fluid, according to a press release from Ceragenix.

Current FDA-approved antimicrobial-coated medical devices rely on drug elution for antibiotic activity. In drug elution, the drug diffuses from the device into surrounding tissue, creating a zone of inhibition against bacterial adhesion. Though effective, this approach only lasts a relatively short time and the bactericidal effect is lost once the drug is gone, according to the release.

In contrast, the antimicrobial coating developed by Ceragenix uses a small molecule mimic of naturally occurring antimicrobial peptides comprising the human body’s innate immune system. These peptides, called cationic steroid antibiotics (CSAs), target bacterial membranes. Ceragenix oficials believe the coating can be firmly attached to medical devices, including orthopedic implants, and should not elute into surrounding tissue.

Data supporting Ceracide’s antimicrobial effect were presented in a poster study at the Interscience Conference on Antimicrobial Agents and Chemotherapy in Washington.

In the study, Paul B. Savage, PhD, a professor of chemistry and biochemistry at Brigham Young University in Provo, Utah, and colleagues covalently bonded CSAs to a polymer and attached thin films of the material onto titanium plates. They then tested antimicrobial activities of the films against both gram-positive and gram-negative bacteria compared with control samples.

The researchers placed the titanium plates in nutrient media or phosphate-buffered saline solutions containing S. aureus and E. coli bacteria, which had become partially opaque due to bacterial growth. They found that bacteria in samples of bare and control-coated titanium plates continued to grow. However, CSA-coated titanium samples prevented bacterial growth, according to the study.

To verify the coating’s antibacterial effect, the researchers soaked a CSA-coated sample in nutrient media for six hours. After removing the sample, they added S. aureus bacteria to the remaining nutrient media. “The bacterial population expanded unchecked, thereby indicating that the CSA remained attached to the plate,” the authors said in the study.

Ceragenix plans to conduct long-term studies assessing the efficacy of the Ceracide coating on various medical devices. The company has also entered into a letter agreement with the Centers for Disease Control and Prevention (CDC) to evaluate the Ceracide coating using the CDC’s biofilm reactor, company officials noted in the press release.

For more information:
Savage PB, Michaelis D, Orsak T, et al. Thin film containing a cationic steroid antibiotic displays bactericidal activity. Poster #3398. Presented at the Interscience Conference on Antimicrobial Agents and Chemotherapy. Dec. 15-19, 2005. Washington. Available online at the Ceragenix Pharm. Inc. Web site: http://www.ceragenix.com/pdf/coatings.pdf.