Comparison of virulence plasmids among clostridium perfringens type E isolates

Jihong Li, Kazuaki Miyamoto, Bruce A McClane

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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 approximately 97 or approximately 135 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 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 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 only amplifies a product 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 re-mobilized and inserted onto other conjugative plasmids or some iap/ibp plasmids acquired additional DNA sequences.
Original languageEnglish
Pages (from-to)1811 - 1819
Number of pages9
JournalInfection and Immunity
Volume75
Issue number4
Publication statusPublished - 2007

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