Capnocytophaga canimorsus is a commensal bacterium of the oral cavity of dogs and cats. This bacterium is known to cause life-threatening conditions in humans through infection of bite wounds (Gaastra and Lipman 2010). Risk factors for these conditions have been identified as immunosuppression in patients with post-transplant or anatomical/functional asplenia (Shahani and Khardori 2014). However, several review articles have also described infections in immunocompetent patients (Mader et al. 2020). In vitro experiments have demonstrated resistance of these bacteria to phagocytosis and immune modulation with low pro-inflammatory macrophage secretion. The overall immunological risk factors during infection are still poorly understood. Infection can evolve into a clinical status similar to sepsis, leading to severe dissemination of intravascular coagulation, multi-organ failure with a fatal outcome. The overall incidence of human infections is underestimated due to the difficulty of culturing and identifying these bacteria. Two cases of these infections have been described and published in the Czech Republic (Hloch et al. 2014; Prasil et al. 2020). C. canis and C. cynodegmi have also been described as species causing life-threatening infections, albeit with a low incidence compared to C. canimorsus (Taki et al. 2018). In view of the increasing number of published cases of infections related to dog or cat injuries (29 publications for the period 2017-2021, WoS), veterinarians need to pay more attention to education among pet owners and have appropriate preventive measures in place to prevent infections, especially in immunocompromised dog and cat owners. The aim of this study was to determine the representation of C. canimorsus and C. cynodegmi in the oral microflora of dogs and to verify the possibility of their decolonization.

A total of 130 dogs were tested for the presence of C. canimorsus. Of this cohort, 90 dogs (69 %) were positive for C. canimorsus and 103 dogs (79 %) were positive for C. cynodegmi. After confirmation of positivity, 6 dogs have entered further testing so far. In vitro test confirmed the inhibitory effect of silver nanoparticles against C. canimorsus, the MIC (minimum inhibitory concentration) in vitro being 0.000015 %. They were treated with a commercially produced mucoadhesive gel containing active silver (0.02 %). Dog owners then applied the gel and collected samples for the determination of C. canimorsus. Repeated application of the gel resulted in the elimination of C. canimorsus in 5 dogs. In one dog the samples were still positive for C. canimorsus despite gel application.Silver nanoparticles appear promising in the decolonization of C. canimorsus from canine oral cavities. The study should be continued with a larger number of dogs and over a longer time frame. The use of RT PCR to quantify oral colonization would also be appropriate. In the case of C. cynodegmi, inhibitory effect of silver nanoparticles appears to be rather negligible. This work was funded by IGA VETUNI grant 104/2022/FVL.