Capsular serovars of virulent Capnocytophaga canimorsus are shared by the closely related species C. canis and C. cynodegmi

Abstract

Capnocytophaga canimorsus is a dog oral commensal bacterium that causes rare but life-threatening generalized infections in humans who have been in contact with its animal hosts. Two other dog commensals, Capnocytophaga canis and Capnocytophaga cynodegmi, cause rare, mild local infections. To date, nine capsular serovars have been described in C. canimorsus. Here, we serotyped 112 strains of Capnocytophaga spp. isolated from human infections. The C. canimorsus strains (86 of 96, 89.6%) belonged to serovars A, B, or C with relative frequencies of approximately 30% for each serovar. The high prevalence of the A, B, and C serovars in strains isolated from humans, compared to the previously described low prevalence of these serovars among dog isolates (7.6%), confirms that these three serovars are more virulent to humans than other serovars and suggests that the low incidence of disease may be linked to the low prevalence of the A, B, and C serovars in dogs. We serotyped six strains of C. canis and ten strains of C. cynodegmi and, surprisingly, found one C. canis and three C. cynodegmi strains to be of capsular serovar B. This observation prompted us to test 34 dog-isolated C. canis and 16 dog-isolated C. cynodegmi strains. We found four C. canis strains belonging to serovar A and one belonging to serovar F. In contrast, no dog-isolated C. cynodegmi strain could be typed with the available antisera. This work demonstrates that virulence-associated capsular polysaccharides (A, B, and C) are not specific to the C. canimorsus species.

These authors contributed equally: Francesco Renzi, Estelle Hess

These authors contributed equally: Francesco Renzi, Estelle Hess

Acknowledgements

This work was supported by grant SOC 1510582 from the Walloon Region and by Proof of Concept grant 780540 “CANITEST” from the ERC.

Authors’ contributions

F.R. and E.H. conceived the study, analyzed and interpreted data, and wrote the manuscript. M.D., D.K., E.C., and M.O. performed the experiments. M.O. and E.M. provided CCUG strains, and E.M. revised the manuscript. G.R.C. conceived and designed the study, analyzed and interpreted the data, and wrote the manuscript.

Conflict of interest

The authors declare that they have no conflict of interest.

Electronic supplementary material

Supplementary Information accompanies this paper at (10.1038/s41426-018-0126-x).

Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.