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Professional and Research Interests:
- Bacterial Pathogenesis
- Molecular pathogenesis of Clostridium perfringens
- Food poisoning
- Non-food-borne human gastrointestinal (GI) diseases
- GI diseases in domestic animals
My laboratory group investigates the molecular pathogenesis of C. perfringens type A isolates associated with C. perfringens type A food poisoning and non-food-borne gastrointestinal (GI) diseases in humans and GI diseases in domestic animals. Specifically, we investigate the molecular mechanisms of i) C. perfringens sporulation ii) sporulation-regulated synthesis of C. perfringens enterotoxin (CPE), a major virulence factor of C. perfringens pathogenesis iii) spore germination, and iv) spore resistance to various stress factors such as, chemicals, heat and high pressure processing.
The gram-positive, spore-forming, anaerobic C. perfringens bacteria is an important cause of both histotoxic and GI diseases in humans and domestic animals. C. perfringens spores are metabolically dormant, are resistant to many environmental insults, and can survive for long periods. Once conditions are favorable, these spores can germinate, outgrow, return to vegetative growth and then release toxins and cause disease. We have shown that C. perfringens spores are resistant to heat, chemicals, UV-radiation and high hydrostatic pressure processing, and the main factors involved in these resistance processes are: i) the small-acid soluble proteins (SASPs) that saturate the spore's DNA; ii) a low spore core water content that protects essential enzymes and DNA in the spore core from environmental insults and is controlled in part by SpmA-B and DacB proteins; iii) the spore's large depot of pyridine-2,6-dicarboxylic acid (dipicolinic acid (DPA)) which is pumped into the spore core during sporulation at least in part by the SpoVA proteins.
One approach to develop efficient therapies against C. perfringens diseases, and considering that C. perfringens spores are the infectious morphotype, is to block or induce germination. Blocking germination would block the resumption of growing vegetative cells, while inducing germination would yield C. perfringens spores that have lost their resistance properties to conventional treatments applied in the food industry and in clinical settings, and thus becoming more sensitive to inactivation by milder treatments. Therefore, basic knowledge on the mechanism of spore germination is warranted. In this respect, we identified for the first time the nutrient germinants (KCl and a mixture of L-asparagine and KCl) and their cognate receptors (GerKA and/or GerKC) required for C. perfringens spore germination. In a following project, we showed that in C. perfringens: i) SpoVA proteins are essential for Ca-DPA uptake by the developing spore during C. perfringens sporulation; and ii) SpoVA proteins and Ca-DPA release, required for Bacillus subtilis signal transduction, are not required for the transduction of the germination signal from the receptors to the cortex-lytic enzymes (CLEs) during C. perfringens spore germination. Recently, we have also found that SleC is an essential CLE for cortex peptidoglycan (PG) hydrolysis during germination of spores of C. perfringens. The hydrolysis of cortex PG is the culminating event in the germination of bacterial spores, and is essential for resumption of enzymatic activity in the spore core and eventual vegetative growth. As a consequence, cortex hydrolysis is essential for spores of any pathogenic organism such as C. perfringens to cause disease. The identification of SleC as the major essential CLE in C. perfringens spores thus makes this enzyme of potential interest for development of inhibitors, since such compounds would block spore germination and thus the ability of spores to cause disease. Cortex hydrolysis also makes the now fully germinated spore much less resistant to common decontamination procedures. Consequently, a drug that could rapidly activate SleC in spores would also be useful, since such a drug would allow decontamination of the now germinated C. perfringens spores under less harsh conditions than needed for destruction of the much more resistant dormant spores.
C. perfringens type A food poisoning currently ranks as the third most commonly reported food-borne disease in the United States. In the U.S. alone C. perfringens type A food poisoning results in annual economic losses of over $120 million dollars. The development of preventive measures against Clostridium perfringens-mediated diseases has been hampered by the lack of understanding of the molecular mechanisms of C. perfringens spore-formation, -germination and -resistance. We anticipate that our research will facilitate the designing and developing a preventive measure against Clostridial diseases.
Sarker MR, Shivers RP, Sparks SG, Juneja VK, McClane BA. 2000. Comparative experiments to examine the effects of heating on vegetative cells and spores of Clostridium perfringens isolates carrying plasmid genes versus chromosomal enterotoxin genes.. Applied and environmental microbiology. 66(8):3234-40.