Clostridium chauvoei, an Evolutionary Dead-End Pathogen.

Lorenz Rychener,Saria In-Albon,Rosangela E Ziech,Piklu Roy Chowdhury,Laurent Falquet,Joachim Frey,Agueda C De Vargas,Steven P Djordjevic,Pamela Nicholson

doi:10.3389/fmicb.2017.01054

Abstract

Full genome sequences of 20 strains of Clostridium chauvoei, the etiological agent of blackleg of cattle and sheep, isolated from four different continents over a period of 64 years (1951–2015) were determined and analyzed. The study reveals that the genome of the species C. chauvoei is highly homogeneous compared to the closely related species C. perfringens, a widespread pathogen that affects human and many animal species. Analysis of the CRISPR locus is sufficient to differentiate most C. chauvoei strains and is the most heterogenous region in the genome, containing in total 187 different spacer elements that are distributed as 30 – 77 copies in the various strains. Some genetic differences are found in the 3 allelic variants of fliC1, fliC2 and fliC3 genes that encode structural flagellin proteins, and certain strains do only contain one or two alleles. However, the major virulence genes including the highly toxic C.chauvoei toxin A, the sialidase and the two hyaluronidases are fully conserved as are the metabolic and structural genes of C. chauvoei. These data indicate that C. chauvoei is a strict ruminant-associated pathogen that has reached a dead end in its evolution.

Highlights

Clostridium chauvoei, a Gram positive, highly pathogenic, strict anaerobic bacterium that is able to sporulate, is the etiologic agent of blackleg, a severe disease of cattle and to a lesser extent of small ruminants
The resulting analysis shows a clustering of the C. chauvoei strains into a European/African/American cluster and an Australia/New Zealand/United Kingdom cluster. This clustering corresponds to that found in the comparison taking into account the four virulence genes cctA, nagI, nagH and nanA or the whole genome Single Nucleotide Variations (SNV) analysis, confirming the phylogenetic clustering that we found with the two latter approaches
Preventive measures by vaccination with empirically developed bacterin vaccines are efficient and protect animals grazing on meadows that are contaminated by spores of C. chauvoei

Summary

Introduction

Clostridium chauvoei, a Gram positive, highly pathogenic, strict anaerobic bacterium that is able to sporulate, is the etiologic agent of blackleg, a severe disease of cattle and to a lesser extent of small ruminants. Pathological lesions of blackleg are mostly found in the muscular tissue of animals, often in leg muscles, from where the pathogen is commonly isolated. The pathogen is taken up via the digestive tract or the respiratory tract from where C. chauvoei migrates to the muscle tissues where the spores remain dormant until specific conditions are generated, as tissular devitalization that promotes anaerobiosis, resulting in their germination, multiplication and production of the exotoxins (Jubb et al, 1991). Blackleg occurs with increased incidence during dry seasons that followed flooding, when the animals have to graze short plants and are closer in contact with their nostrils and muzzles to soil where the pathogen spreads during the preceding flooding

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Conclusion