In Vitro Killing Activity of Crevicular Concentrations of Tinidazole Plus Common Oral Antibiotics Against High‐Density Mixed Inocula of Periodontal Pathogens in Strict Anaerobic Conditions

Background: Odontogenic infections are polymicrobial. This study explores the in vitro killing activity by concentrations similar to those found in crevicular fluid of tinidazole in combination with amoxicillin/clavulanic acid, clindamycin and levofloxacin against four groups of high‐density mixed inocula of anaerobes (Prevotella buccae, Fusobacterium nucleatum, and Veillonella spp.) and facultative (Capnocytophaga spp. and Streptococcus spp.) isolates of periodontal pathogens. Methods: Killing curves were assessed under strict anaerobic conditions with antibiotics alone and in combination with tinidazole at concentrations similar to those achieved in crevicular fluid against ∼107 colony forming units (CFU)/ml inoculum (1:1:1:1:1 proportion of the five bacterial isolates) of the four bacterial groups. Group 1 did not include β‐lactamase–producing strains; groups 2, 3, and 4 included one, two, and three β‐lactamase–producing strains, respectively. Results: In single‐drug experiments, at 48 hours, tinidazole alone did not show significant killing of the entire bacterial population, whereas reductions in the initial inocula ≥2.09 log10 CFU/ml with clindamycin, ≥3.26 log10 CFU/ml with amoxicillin/clavulanic acid, and ≥3.83 log10 CFU/ml with levofloxacin were obtained. When combined with tinidazole, reductions were significantly higher for all antibiotics: ≥5.28 log10 CFU/ml with clindamycin, ≥4.78 log10 CFU/ml with amoxicillin/clavulanic acid, and ≥6.17 log10 CFU/ml with levofloxacin. Conclusion: In addition to its high activity against anaerobic periodontal pathogens, tinidazole offered synergism with other antibiotics against the large strict anaerobic subpopulation and the small facultative subpopulation of a high‐density mixed inocula of odontogenic pathogens under strict anaerobic conditions, similar to those of odontogenic infections.