SUMMARY In both humans and animals, Clostridium perfringens is an important cause of histotoxic infections and diseases originating in the intestines, such as enteritis and enterotoxemia. The virulence of this Gram-positive, anaerobic bacterium is heavily dependent upon its prolific toxin-producing ability. Many of the ∼16 toxins produced by C. perfringens are encoded by large plasmids that range in size from ∼45 kb to ∼140 kb. These plasmid-encoded toxins are often closely associated with mobile elements. A C. perfringens strain can carry up to three different toxin plasmids, with a single plasmid carrying up to three distinct toxin genes. Molecular Koch's postulate analyses have established the importance of several plasmid-encoded toxins when C. perfringens disease strains cause enteritis or enterotoxemias. Many toxin plasmids are closely related, suggesting a common evolutionary origin. In particular, most toxin plasmids and some antibiotic resistance plasmids of C. perfringens share an ∼35-kb region containing a Tn 916 -related conjugation locus named tcp (transfer of clostridial plasmids). This tcp locus can mediate highly efficient conjugative transfer of these toxin or resistance plasmids. For example, conjugative transfer of a toxin plasmid from an infecting strain to C. perfringens normal intestinal flora strains may help to amplify and prolong an infection. Therefore, the presence of toxin genes on conjugative plasmids, particularly in association with insertion sequences that may mobilize these toxin genes, likely provides C. perfringens with considerable virulence plasticity and adaptability when it causes diseases originating in the gastrointestinal tract.

Clostridium perfringens type B or D isolates, which cause enterotoxemias or enteritis in livestock, produce epsilon toxin (ETX). ETX is exceptionally potent, earning it a listing as a CDC class B select toxin. Most C. perfringens strains also express up to three different sialidases, although the possible contributions of those enzymes to type B or D pathogenesis remain unclear. Type D isolate CN3718 was found to carry two genes (nanI and nanJ) encoding secreted sialidases and one gene (nanH) encoding a cytoplasmic sialidase. Construction in CN3718 of single nanI, nanJ and nanH null mutants, as well as a nanI/nanJ double null mutant and a triple sialidase null mutant, identified NanI as the major secreted sialidase of this strain. Pretreating MDCK cells with NanI sialidase, or with culture supernatants of BMC206 (an isogenic CN3718 etx null mutant that still produces sialidases) enhanced the subsequent binding and cytotoxic effects of purified ETX. Complementation of BMC207 (an etx/nanH/nanI/nanJ null mutant) showed this effect is mainly attributable to NanI production. Contact between BMC206 and certain mammalian cells (e.g., enterocyte-like Caco-2 cells) resulted in more rapid sialidase production and this effect involved increased transcription of BMC206 nanI gene. BMC206 was shown to adhere to some (e.g. Caco-2 cells), but not all mammalian cells, and this effect was dependent upon sialidase, particularly NanI, expression. Finally, the sialidase activity of NanI (but not NanJ or NanH) could be enhanced by trypsin. Collectively these in vitro findings suggest that, during type D disease originating in the intestines, trypsin may activate NanI, which (in turn) could contribute to intestinal colonization by C. perfringens type D isolates and also increase ETX action.

Bismuth oxychloride (BiOCl) sub-microcrystals with tunable morphologies from nanoflakes to hollow microspheres (HMSs) have been synthesized by hydrolyzing a hierarchical precursor (BiCl 3 ) in a solution of water and ethanol with the addition of poly(vinylpyrrolidone) (PVP) and citric acid. The obtained BiOCl possessed sub-microcrystals from single crystals to polycrystals. The formation of the nestlike and hollow structure was found to be induced by citric acid and PVP. The crystal growth and morphology control of BiOCl were explored. Interestingly, citric acid was utilized both as a crystal-growth-inducing agent and a structure-directing agent. The morphology and compositional characteristics of BiOCl were investigated by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Raman, and UV−vis spectra. The photocatalytic activities of BiOCl with different structures have also been investigated by the degradation of Rhodamine-B (RhB) dye under ultraviolet light irradiation. The as-prepared BiOCl exhibited much higher photocatalytic activity than the comzmon one. In particular, the three-dimensional hierarchical structure such as microflowers and HMSs can effectively improve photocatalytic activity. The results show that BiOCl sub-microcrystals have promise as a novel material for photocatalytic applications.

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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.