Comparison of Virulence Plasmids among Clostridium perfringens Type E Isolates

Abstract

Clostridium perfringens type E isolates produce iota-toxin, which is encoded by iap and ibp genes. Using Southern blot analyses, the current study identified iap/ibp plasmids of ϳ97 or ϳ135 kb among eight type E isolates. For most of these isolates, their iap/ibp plasmid also encoded urease and lambda-toxin. However, the beta2-toxin gene, if present, was on a different plasmid from the iap/ibp plasmid. For all isolates, the iap/ibp plasmid carried a tcp locus, strongly suggesting that these plasmids are conjugative. Overlapping PCR analyses demonstrated some similarity between the iap/ibp plasmids and enterotoxin-encoding plasmids of type A isolates. Additional PCR analyses demonstrated that the iap/ibp locus is located near dcm sequences, an apparent plasmid hot spot for toxin gene insertion, and that two IS1151-related sequences are present in the iap/ibp locus. To begin testing whether those IS1151-like sequences can mobilize iap/ibp genes, a PCR assay was performed that amplifies a product only from circular DNA forms that could represent transposition intermediates. This PCR assay detected circular forms containing iap/ibp genes and silent enterotoxin gene sequences, with or without an IS1151-like sequence. Collectively, these results suggest that a mobile genetic element carrying iap/ibp has inserted onto a tcp-carrying enterotoxin plasmid in a type A isolate, creating a progenitor iap/ibp plasmid. That plasmid then spread via conjugation to other isolates, converting them to type E. Further iap/ibp plasmid diversity occurred when either the iap/ibp genes later remobilized and inserted onto other conjugative plasmids or some iap/ibp plasmids acquired additional DNA sequences.

Toxin Plasmids of Clostridium perfringens

“…This ϳ65-kb plasmid has a pCPF4969 backbone but does not encode lambda-toxin or urease (23). In all examined type E isolates, the iap/ibp-carrying plasmid has a tcp locus, strongly suggesting that these plasmids are conjugative (18,23).…”

“…Two major families of iotatoxin plasmids have been identified, the first of which includes large plasmids, varying in size from ϳ97 kb to ϳ135 kb, with a pCPF5603 backbone (18). These iota-toxin plasmids carry functional iap/ibp genes, but their adjacent cpe sequences are silent due to extensive mutations in the cpe gene (18,22). This iap/iab-carrying plasmid family also encodes urease and lambda-toxin (18).…”

“…These iota-toxin plasmids carry functional iap/ibp genes, but their adjacent cpe sequences are silent due to extensive mutations in the cpe gene (18,22). This iap/iab-carrying plasmid family also encodes urease and lambda-toxin (18). The second iota-toxin plasmid family, which includes the recently sequenced plasmid pCPPB-1, carries expressed iap/ibp and cpe genes (23).…”

“…It has now become clear that many important C. perfringens toxins are encoded by large plasmids (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24). Other recent studies, described later in this review, have provided important insights into the diversity of C. perfringens toxin plasmids, the critical importance of these plasmids for pathogenesis, and the ability of toxin plasmids to transfer among C. perfringens strains.…”

Toxinotyping ofClostridium perfringensFecal Isolates of Reintroduced Père David's Deer (Elaphurus davidianus) in China

“…This bacterium might provoke sudden death syndrome in ruminants, enteric disease in domestic animals and humans, food poisoning in humans, and gas gangrene in animals (Songer 1996;Embury-Hyatt et al 2005;Li et al 2007a). Clostridium perfringens is classified into five toxin types (A-E) according to the production of four major toxins, namely alpha (CPA), beta (CPB), epsilon (ETX), and iota (ITX) (Sipos et al 2003;Gharaibeh et al 2010).…”