Abstract
ABSTRACTCapnocytophaga canimorsus is a dog oral commensal that causes rare but severe infections in humans. C. canimorsus was recently shown to be endowed with a capsular polysaccharide implicated in resistance to the innate immune system of the host. Here, we developed the first C. canimorsus capsular serotyping scheme. We describe nine different serovars (A to I), and this serotyping scheme allowed typing of 25/25 isolates from human infections but only 18/52 isolates from dog mouths, indicating that the repertoire of capsules in the species is vast. However, while only three serovars (A, B, and C) covered 88% of the human isolates tested (22/25), they covered only 7.7% of the dog isolates (4/52). Serovars A, B, and C were found 22.9-, 14.6-, and 4.2-fold more often, respectively, among human isolates than among dog isolates, with no geographical bias, implying that isolates endowed with these three capsular types are more virulent for humans than other isolates. Capsular serotyping would thus allow identification of virulent isolates in dogs, which could contribute to the prevention of these infections. To this end, we developed a PCR typing method based on the amplification of specific capsular genes.
Highlights
Capnocytophaga canimorsus is a dog oral commensal that causes rare but severe infections in humans
Whole bacteria were digested with proteinase K, and bacterial polysaccharides were analyzed by Western blotting using an antiserum directed against Cc5 bacteria and adsorbed with the noncapsulated Cc5 transposon mutant Y1C12 [20, 24]
The serum recognized a high-molecular-weight (HMW) band (Ͼ250,000) in the extracts from Cc5 and from 10 other isolates, namely, Cc1 (BCCM/LMG 11511, CCUG 17234, strain P810, strain SSI P810), Cc2, Cc3, Cc10 (BCCM/LMG 11541, CCUG 24741, ATCC 35978, CDC C8936), Cc13, Cc15, Cc21 (CCUG 60839), Cc22 (CCUG 20318), Cc24 (CCUG 67384), and Cc25 (CCUG 66222) (Fig. 1A). Since this band was identified as the capsular polysaccharide (CPS) of Cc5 [20], we concluded that the capsular serovar of Cc5 was shared with these 10 isolates, representing 44% of our collection of human isolates
Summary
Capnocytophaga canimorsus is a dog oral commensal that causes rare but severe infections in humans. We describe nine different serovars (A to I), and this serotyping scheme allowed typing of 25/25 isolates from human infections but only 18/52 isolates from dog mouths, indicating that the repertoire of capsules in the species is vast. Capsular serotyping would allow identification of virulent isolates in dogs, which could contribute to the prevention of these infections. To this end, we developed a PCR typing method based on the amplification of specific capsular genes. We show that 25 isolates of C. canimorsus out of 25 from a collection of isolates from human infections are endowed with a CPS and that those polysaccharide structures present limited variability, with 3 dominant capsular serovars. This study paves the way toward prevention of these dramatic infections
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