The Effect of Varying Ratios of Vancomycin and Tetracycline, and Possible Antibiotic Interaction, on the Colonization of Titanium Alloy by S. aureus and E. coli

Date of Award


Degree Type


Degree Name

Master of Science in Biomedical Sciences

First Advisor

Christopher Adams, PhD

Second Advisor

Denah Appelt, PhD

Third Advisor

Dawn Shell, PhD

Fourth Advisor

Marcus Bell, PhD


Recent research has yielded some promising findings in the prevention of bacterial infections associated with orthopedic implants. Attachment of specific antibiotics to titanium surfaces has been shown to prevent bacterial colonization by both Gram-positive and Gram-negative bacteria. We hypothesized that there is an optimal ratio of vancomycin and tetracycline attached to titanium alloy that inhibits bacterial colonization. We tested this hypothesis by modifying titanium (Ti) pins with different ratios of vancomycin and tetracycline and incubating those Ti-pins with Staphylococcus aureus or Escherichia coli. Immunofluorescence and confocal analysis showed attachment of vancomycin correlated with the incubation concentration of vancomycin while tetracycline did not. Confocal imaging showed that prevention of S. aureus colonization also correlated with the amount of bound vancomycin. For E. coli, dual antibiotic Ti-pins were as, if not more, effective compared to 100% tetracycline. Colony counting showed that 50:50 Ti-pins were most effective against S. aureus, while dual antibiotic Ti-pins had no increased efficacy against E. coli relative to 100% tetracycline. Previous research had showed that when two antibiotics (vancomycin and tetracycline) are tethered to titanium in a 50:50 ratio, this surface proves even more effective at preventing colonization than either alone. Thus, we tested the hypothesis that there is an interaction between the two antibiotics increasing their efficacy against S. aureus and E. coli by incubating varying ratios of vancomycin and tetracycline with planktonic S. aureus or E. coli and evaluated the effect of each antibiotic on the antimicrobial activity of the other. Results of a potential antibiotic interaction showed that vancomycin and tetracycline showed no synergistic interaction on the killing of either S. aureus or E. coli. 9 Determining the optimal ratio of vancomycin to tetracycline at reducing each antibiotics minimum inhibitory concentration (MIC) will help in creating an orthopedic implant surface that is more resistant to bacterial infection. This determination could lead to vastly decreased morbidity and mortality rates associated with peri-prosthetic infections commonly seen in arthroplasty procedures.

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