Diversity of Capnocytophaga species in children and description of Capnocytophaga leadbetteri sp. nov. and Capnocytophaga genospecies AHN8471.

Bacteria of the genus Capnocytophaga form part of the resident oral flora in children and adults. They are recognized as opportunistic pathogens of various extra-oral infections. The significance of individual species in periodontal and extra-oral diseases is unclear, due to the inability of conventional phenotypic tests to identify clinical isolates to species level. Aiming at a clear distinction between species, we undertook a phylogenetic study of a collection of 102 Capnocytophaga strains including 62 oral isolates from children and 40 reference strains from oral and extra-oral infections representing the five known, human, oral Capnocytophaga species. The phylogeny was estimated on the basis of multilocus enzyme electrophoresis (MLEE) of 12 intracellular, housekeeping enzymes and by partial 16S rRNA gene sequencing, and was compared to phenotypic characteristics. The clustering profiles in the MLEE and sequence-based dendrograms were concordant and allowed identification of isolates to species level, based on co-clustering with reference strains. The study confirmed Capnocytophaga ochracea and Capnocytophaga sputigena as separate species, and underlined the problems of distinguishing between them by conventional phenotypic tests. The presence of two distinct clusters of oral isolates from children indicated the existence of novel species, supported by analysis of near-full-length 16S rRNA gene sequences and by DNA-DNA hybridization results. One cluster of weakly saccharolytic isolates without the ability to ferment sucrose is proposed as Capnocytophaga leadbetteri sp. nov. (type strain AHN8855(T)=CCUG 51857(T)=NCTC 13375(T)). Another cluster not phenotypically distinguishable from C. ochracea and C. sputigena is designated Capnocytophaga genospecies AHN8471 (represented by strain AHN8471=CCUG 51856=NCTC 13374).