Clostridium perfringens Spores: Inactivation, Germination, and Formation.

摘要

The enterotoxin-producing Clostridium perfringens type A isolates are responsible for the third most common foodborne illness in the United States and can also cause non-foodborne human gastrointestinal (GI) diseases such as antibiotic-associated and sporadic diarrheas.;In the first study, the antimicrobial peptide nisin was evaluated for its antimicrobial effect against enterotoxigenic C. perfringens food poisoning (FP) and non-foodborne (NFB) GI disease isolates. Nisin did not affect spore germination, whereas germinated spores were very susceptible to low concentration of nisin and thus spores outgrowth were arrested. Nisin also exerted its inhibitory effect against vegetative growth of C. perfringens FP and NFB isolates in rich medium; however, FP cells were less resistant to nisin than NFB cells. Nevertheless, nisin was not effective in controlling germination and outgrowth of C. perfringens spores in cooked meat products during storage at abusive temperature, even at ~ 4 times elevated concentration than the regulatory approved level.;The main focus of the second study was to develop an effective spore inactivation strategy on food contact surfaces by inducing spore germination prior to inactivation of the more susceptible spores with commonly used surface disinfecting agents. The mixture of L-asparagine and KCl (AK) was the most effective germinant for spores of enterotoxigenic C. perfringens type A. Germination temperature had a significant influence on the germination extent and subsequent inactivation by variety of surface disinfectants.;Spore germination is initiated upon sensing a variety of compounds, termed germinants, via the cognate germinant receptors. In the third study, we identified sodium ions and inorganic phosphate (NaPi) at pH ~ 6.0 as a novel germinant for spores of enterotoxin-producing C. perfringens FP isolates. The spores lacking germination proteins GerAA and GerKA-KC were severely impaired in their ability to germinate with NaPi, whereas GerKB-negative spores germinated to a similar extent as wild type spores with NaPi, but their initial rate of germination was lesser. Spores lacking GerO or GerO GerQ germinated to a lower extent and with a significantly slower rate than wild type spores.;In the fourth study, we demonstrated that polar, uncharged amino acids at pH 6.0 could efficiently trigger germination of spores of enterotoxigenic C. perfringens. While L-glutamine is a unique nutrient germinant for spores of C. perfringens FP isolates, L-asparagine, L-cysteine, L-serine, and L-threonine can induce germination of both FP and NFB spores. The germinant receptor GerKC is the major receptor involved in cysteine- and glutamine-induced germination and release of dipicolinic acid (DPA) from the spore’s core, whereas less pronounced germination defects were observed in gerAA and gerKB spores. GerKC also has a key role in L-asparagine germination. For serine and threonine (pH 6.0)-induced germination, GerKA is the dominant receptor and GerKC and GerKB are also required for efficient germination of FP spores.;The objectives of the fifth study were to identify and characterize the putative sensor histidine kinases of C. perfringens. We identified six genes encoding putative sporulation-associated sensor histidine kinases in the genome of C. perfringens SM101. These putative kinase genes were highly expressed under sporulation-stimulating conditions. Spores of two kinase mutants also exhibited slower outgrowth than their parental strain; however, no difference in colony forming efficiency was observed among tested strains. Additionally, mutations in cpr1728 and cpr1055 did not affect vegetative growth; however, both mutants grew at higher rate under sporulation-inducing conditions. (Abstract shortened by UMI.).