The Enterotoxic Clostridia
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The Enterotoxic Clostridia BRUCE A. MCCLANE, FRANCISCO A. UZAL, MARIANO E. FERNANDEZ MIYAKAWA, DAVID LYERLY AND TRACY WILKINS
Introduction to the Enterotoxic Clostridia The anaerobic, nutrient-rich conditions of the mammalian gastrointestinal (GI) tract provide a relatively attractive niche for many clostridia. Several of those clostridial species also produce toxins with potent activity on the GI tract, enabling them to cause human and/or veterinary enteric diseases (Table 1). Clostridial enteric diseases vary considerably (as described in the Clinical Disease and Epidemiology sections of this chapter) but can be quite common and severe. Collectively, these infections place a major economic burden on human and veterinary medicine, draining billions of dollars per year from the economy. This chapter focuses on the two most important enterotoxic clostridial species for human and veterinary enteric diseases, i.e., Clostridium perfringens and Clostridium difficile.
Clostridium perfringens Introduction Clostridium perfringens has a ubiquitous environmental distribution, including a presence in the normal GI flora of humans and domestic animals. Under favorable conditions, this bacterium can cause a wide array of enteric and histotoxic infections. This chapter focuses on the medical and veterinary enteric diseases caused by C. perfringens; the histotoxic infections caused by this bacterium are discussed in a separate chapter.
Historical Perspective Clostridium perfringens has been linked to human GI disease since the mid-1940s, when McClung first noted this bacterium’s ability to cause food poisoning (McDonel, 1986). This tentative association was confirmed by the classic studies of Hobbs during the 1950s (McDonel,
1986). In the late 1940s, C. perfringens also became associated with outbreaks of darmbrand (enteritis necroticans) in post-war Germany (Lawrence, 1997). The early 1980s saw the first linkage of C. perfringens with human nonfoodborne GI diseases (Borriello et al., 1984; Borriello, 1995). The association of C. perfringens with veterinary enteric disease occurred even earlier, with initial reports surfacing in the 1920s and early 1930s (Songer, 1996). Appreciation of the full scope of C. perfringens veterinary diseases increases to this day.
Phylogeny The genus Clostridium consists of nearly 150 phylogenetically heterogeneous species that do not represent a coherent taxon (Stackebrandt, 1997). Using 16S ribosomal RNA sequence analyses, 19 different clostridial species clusters have been defined (Stackebrandt, 1997; Stackebrandt et al., 1999). Along with most other pathogenic clostridial species (except C. difficile), C. perfringens belongs to phylogenetic cluster I, which is considered the core cluster of the genus Clostridium. Within that core cluster, C. perfringens belongs to the same Ia subcluster that also includes Clostridium botulinum.
Taxonomy Clostridium perfringens is a Gram-positive, nonmotile, short-to-intermediate sized rod, often with a “box-car
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