Clostridium perfringens and Histotoxic Disease
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Clostridium perfringens and Histotoxic Disease JULIAN I. ROOD
Introduction The clostridia are a diverse group of Grampositive spore-forming bacteria that cause a variety of potentially fatal human diseases including gas gangrene, tetanus, botulism and pseudomembranous colitis. The common feature of all of these diseases is that spore formation is important in their epidemiology and that they are mediated by powerful protein toxins. Since these syndromes are best discussed on a systemsrelated basis, rather than by their causative bacterial species, the clostridial chapters have been divided into separate discussions on the neurotoxic (Neurotoxigenic Clostridia in this Volume), enterotoxic (The Enterotoxic Clostridia in this Volume) and histotoxic clostridia. For earlier reviews on these topics see Rood et al. (1997) and Fischetti et al. (2000). The reader is also referred to McLennan’s classical review of histotoxic clostridial infections of man (MacLennan, 1962) and a more recent review of clostridial diseases of animals (Songer, 1996). The emphasis of this chapter, and those associated with it, will be on the pathogenesis of these clostridial diseases and the structure and function of the toxins. This chapter will focus on clostridial myonecrosis, or gas gangrene, caused by Clostridium perfringens. It will also include a discussion of the genetics and genomic analysis of this organism, which is the most intensively studied clostridial species.
Phylogeny The clostridia are a very heterogenous group of bacteria that were originally classified in the same genus because they were Gram-positive rods that had the ability to form heat-resistant endospores and grew only under anaerobic conditions. The genus is now much more diverse and includes Gram-negatives, non-sporeformers and aerobes. Therefore, taxonomically the clostridia are much more disparate than most bacterial genera: if it wasn’t for their medical
significance, they would be broken up into many different genera. On the basis of their 16S rRNA sequences, they can be divided into 19 clusters that are intermingled with members of other genera (Collins et al., 1994; Stackebrandt et al., 1999). C. perfringens, along with C. septicum and C. novyi, as well as C. botulinum and C. tetani, belongs to cluster I, which also includes the type strain C. butyricum (Fig. 1). By contrast, C. difficile and C. sordellii belong to cluster XI. Even within species there is considerable taxonomic confusion. For example, 16S rDNA sequence analysis indicates that C. novyi types B and C and C. histolyticum probably represent a single species that is more closely related to C. botulinum types C and D than to C. novyi type A (Sasaki et al., 2001a). Subsequent phylogenetic analysis of the flagellin gene fliC indicates that C. novyi type B and C. histolyticum can be differentiated from one another (Sasaki et al., 2002). It is time for the phylogenetic reclassification of the clostridia, but this process would pr
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