Results: Doxycycline reduced spirochetal structures ~90% but increased the number of round body forms about twofold. Amoxicillin reduced spirochetal forms by ~85%–90% and round body forms by ~68%, while treatment with metronidazole led to reduction of spirochetal structures by ~90% and round body forms by ~80%. Tigecycline and tinidazole treatment reduced both spirochetal and round body forms by ~80%–90%. When quantitative effects on biofilm-like colonies were evaluated, the five antibiotics reduced formation of these colonies by only 30%–55%. In terms of qualitative effects, only tinidazole reduced viable organisms by ~90%. Following treatment with the other antibiotics, viable organisms were detected in 70%–85% of the biofilm-like colonies.
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