Organization of the PlasmidcpeLocus inClostridium perfringensType A Isolates

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Abstract
Clostridium perfringenstype A isolates causing food poisoning have a chromosomal enterotoxin gene (cpe), whileC. perfringenstype A isolates responsible for non-food-borne human gastrointestinal diseases carry a plasmidcpegene. In the present study, the plasmidcpelocus of the type A non-food-borne-disease isolate F4969 was sequenced to design primers and probes for comparative PCR and Southern blot studies of thecpelocus in other type A isolates. Those analyses determined that the region upstream of the plasmidcpegene is highly conserved among type A isolates carrying acpeplasmid. The organization of the type A plasmidcpelocus was also found to be unique, as it contains IS1469sequences located similarly to those in the chromosomalcpelocus but lacks the IS1470sequences found upstream of IS1469in the chromosomalcpelocus. Instead of those upstream IS1470sequences, a partial open reading frame potentially encoding cytosine methylase (dcm) was identified upstream of IS1469in the plasmidcpelocus of all type A isolates tested. Similardcmsequences were also detected in severalcpe-negativeC. perfringensisolates carrying plasmids but not in type A isolates carrying a chromosomalcpegene. Contrary to previous reports, sequences homologous to IS1470, rather than IS1151, were found downstream of the plasmidcpegene in most type A isolates tested. Those IS1470-like sequences reside in about the same position but are oppositely oriented and defective relative to the IS1470sequences found downstream of the chromosomalcpegene. Collectively, these and previous results suggest that thecpeplasmid of many type A isolates originated from integration of acpe-containing genetic element near thedcmsequences of aC. perfringensplasmid. The similarity of the plasmidcpelocus in many type A isolates is consistent with horizontal transfer of a commoncpeplasmid amongC. perfringenstype A strains.