Alteration in ultrastructure and germination of Clostridium perfringens type A spores following extraction of spore coats

Distribution of Enterotoxin- and Epsilon-Positive Clostridium perfringens Spores in U.S. Retail Spices

The role of spices as vehicles of foodborne illness prompted an examination of bacterial spores in these products. Here, we report on the levels and characteristics of spores of Clostridium perfringens associated with 247 U.S. retail spices. Forty-three confirmed isolates from 17% of samples were obtained, present at levels ranging from 3.6 to 2,400/g. Twenty-seven (63%) of C. perfringens isolates were positive for the enterotoxin gene ( cpe). Seven random spice isolates produced enterotoxin at levels of between 4 and 16 ng/mL, compared with three outbreak (control) strains that each produced enterotoxin levels of >1,024 ng/mL. D_95°C levels (1.0 to 3.3 min) of spores of four randomly selected spice isolates suggests a plasmid-localized cpe, while one had D_95°C (>45 min) consistent with chromosomally located cpe. Five of the 43 isolates possessed the epsilon toxin gene ( etx, as well as cpe). Foods could easily become contaminated with spores of cpe-positive C. perfringens by the addition of spices. Because of its spore-forming ability, its rapid generation times at elevated temperatures, improper heating, cooling, and holding conditions could lead to elevated levels of C. perfringens in foods, a requirement for its implication in foodborne outbreaks.

Akwaton, polyhexamethylene-guanidine hydrochloride-based sporicidal disinfectant: a novel tool to fight bacterial spores and nosocomial infections

Bacterial spores are of continuing interest to the food and medical industries. In efforts to eliminate bacterial spore contamination, a number of sporicidal agents have been developed. Most of these compounds must be used carefully in very specific circumstances as they are toxic to humans. The sporicidal activity of Akwaton, a polyhexamethylene-guanidine hydrochloride (PHMGH)-based disinfectant, was tested against Bacillus subtilis spores. PHMGH is a colourless, odourless, non-corrosive and non-irritating antimicrobial biocide of the guanidine family. Spores suspended in distilled water and spores placed on solid surfaces (stainless steel and glass) were used to determine the log(10) reduction after exposure to varying concentrations of Akwaton. The minimum sporostatic concentration, the minimum sporicidal concentration and the time required for sporicidal activity corresponded to 0.06% (w/v), 0.08 % (w/v) and 8.5 min, respectively. Disinfectant concentrations of 0.24 % (w/v) and 0.44 % (w/v) killed all spores suspended in distilled water within 3 min and 90 s, respectively. The sporicidal activity against suspended spores was linearly dependent with respect to the concentration of PHMGH and contact time (y(3 min) = 40x-1.6 and y(90 s) = 20x-0.8 thus y(3 min) = 2y(90 s)). Spores placed on surfaces were more resistant to the effect of the disinfectant and the positive linear correlation between the sporicidal activity and concentration was not observed. The concentration required to kill all spores placed on a surface (stainless steel or glass) corresponded to 0.52 % (w/v) for 90 s of contact and 0.36 % (w/v) for 3 min. This study demonstrated that PHMGH is an effective sporicidal disinfectant with great potential for use in hospitals, laboratories, food industries and households.

Survival of Escherichia coli after isoelectric solubilization and precipitation of fish protein

Protein recovery for fish processing by-products utilizes extreme pH shifts for isoelectric solubilization and precipitation. The purpose of this study was to determine if Escherichia coli would survive exposure to the extreme pH shifts during the protein recovery process. Fresh rainbow trout were beheaded, gutted, and minced and then inoculated with approximately 10(9) CFU of E. coli ATCC 25922 per g, homogenized, and brought to the target pH of 2.0, 3.0, 11.5, or 12.5 by the addition of concentrated hydrochloric acid or sodium hydroxide to solubilize muscle proteins. The homogenate was blended and centrifuged to separate the lipid and insoluble components (bones, skin, insoluble protein, etc.) from the protein solution. The protein solution was subjected to a second pH shift (pH 5.5) resulting in protein precipitation that was recovered with centrifugation. Microbial analysis was conducted on each fraction (i.e., lipid, insoluble components, protein, and water) with selective and nonselective media. The sums of the surviving E. coli in these fractions were compared with the initial inoculum. The greatest total microbial reduction occurred when the pH was shifted to 12.5 (P < 0.05), i.e., a 4.4-log reduction of cells on nonselective media and a 6.0-log reduction of cells on selective media. The use of selective and nonselective media showed that there was significant (P < 0.05) injury sustained by cells exposed to alkaline treatment (pH 11.5 and 12.5) in all fractions except the insoluble fraction at pH 11.5. Increasing the exposure time or the pH may result in greater bacterial reductions in the recovered protein.

Destruction of gram-negative food-borne pathogens by high pH involves disruption of the cytoplasmic membrane

High pH has been shown to rapidly destroy gram-negative food-borne pathogens; however, the mechanism of destruction has not yet been elucidated. Escherichia coli O157:H7, Salmonella enteritidis ATCC 13706, and Listeria monocytogenes F5069 were suspended in NaHCO3-NaOH buffer solutions at pH 9, 10, 11, or 12 to give a final cell concentration of approximately 5.2 x 10(8) CFU/ml and then held at 37 or 45 degrees C. At 0, 5, 10, and 15 min the suspensions were sterilely filtered and each filtrate was analyzed for material with A260. Viability of the cell suspensions was evaluated by enumeration on nonselective and selective agars. Cell morphology was evaluated by scanning electron microscopy and transmission electron microscopy. A260 increased dramatically with pH and temperature for both E. coli and S. enteritidis; however, with L. monocytogenes material with A260 was not detected at any of the pHs tested. At pH 12, numbers of E. coli and S. enteritidis decreased at least 8 logs within 15 s, whereas L. monocytogenes decreased by only 1 log in 10 min. There was a very strong correlation between the initial rate of release of material with A260 and death rate of the gram-negative pathogens (r = 0.997). At pH 12, gram-negative test cells appeared collapsed and showed evidence of lysis while gram-positive L. monocytogenes did not, when observed by scanning and transmission electron microscopy. It was concluded that destruction of gram-negative food-borne pathogens by high pH involves disruption of the cytoplasmic membrane.

Interaction of iodine with Bacillus subtilis spores and spore forms

Buffered solutions of iodine (pH 7.0) were effective against Bacillus subtilis spores, but concentrations and contact times for effective sporicidal action were relatively high. Concentrations of 500 to 1000 ppm available iodine with a contact time of 30-45 min were required to produce a 3-5 log reduction. Treatment of spores with agents which caused progressive extraction of coat protein and cortex hexosamine was associated with increased sensitivity to iodine. Treatment of spores with iodine produced extraction of spore coat protein which was potentiated in the presence of NaOH, but there was no evidence of breakdown of cortex hexosamines or release of dipicolinic acid, either from intact spores or spore protoplasts. Sporicidal concentrations of iodine stimulated the uptake of (32P) phosphate over an initial period of 30-40 min, but phosphate then leaked from the cells; 1000 ppm available iodine produced total loss within 60 min. Results of this investigation are consistent with previous findings which suggest that the resistance of spores to biocides is related to the barrier properties of the spore outer layers and that the sporicidal action of halogen-releasing agents is related to their ability to cause coat and cortex degradation, leading to rehydration of the spore protoplast and allowing diffusion to their site of action on the underlying protoplast.

Interaction of Bacillus subtilis spores with sodium hypochlorite, sodium dichloroisocyanurate and chloramine-T

Solutions of chlorine-releasing agents (CRAs) show varying activity against Bacillus subtilis spores; sodium hypochlorite (NaOCl) shows higher activity than sodium dichloroisocyanurate (NaDCC) which is more active than chloramine-T. Investigations with coat- and cortex-extracted spores indicate that resistance to CRAs depends not only on the spore coat but also the cortex. Whereas extraction of alkali-soluble coat protein increased sensitivity to NaOCl and NaDCC, degradation of coat and cortex material was required to achieve significant activity with chloramine-T. NaOCl (in the presence and absence of NaOH) and NaDCC (in the presence of NaOH only) produced degradation of spore coat and cortex material which may be related to their rapid sporicidal action at low concentrations under these conditions. By contrast, chloramine-T produced no degradation of cortex peptidoglycan and was only effective against normal and alkali-treated spores at high concentrations, requiring extraction of peptidoglycan with urea/dithiothreitol/sodium lauryl sulphate (UDS) or UDS/lysozyme to achieve significant activity at low concentrations. Results suggest that the sporicidal action of CRAs is associated with spore coat and cortex degradation causing rehydration of the protoplast allowing diffusion to the site of action on the underlying protoplast.

Bacterial spores and chemical sporicidal agents

Bacterial spores are among the most resistant of all living cells to biocides, although the response depends on the stage of sporulation. The development of resistance to some agents such as chlorhexidine occurs much earlier in sporulation than does resistance to glutaraldehyde, which is a very late event. During germination or outgrowth or both, resistance is lost and the cells become as susceptible to biocides as nonsporulating bacteria. Mechanisms of spore resistance to, and the action of, biocides are discussed, and possible means of enhancing antispore activity are considered. The clinical and other uses of sporicidal and sporostatic chemical agents are described.

Activation of Clostridium perfringens spores under conditions that disrupt hydrophobic interactions of biological macromolecules

The effect of hydrophobic interactions on the activation of C. perfringens NCTC 8679 spores was examined by heating spores under conditions that modify the hydrophobic properties of biological macromolecules. After the activation treatment and a washing procedure, germination was determined by measuring the decrease in optical density of spores suspended in an enriched germination medium. Activation was inhibited for spores that were treated under conditions that strengthen hydrophobic interactions, i.e., a decrease in pH or the presence of structure-stabilizing neutral salts. Activation was enhanced by treatment under conditions that disrupt hydrophobic interactions, i.e., an increase in pH or the presence of urea, dibucaine, or denaturing neutral salts. A deactivation treatment with the antichaotropic salt (NH4)2SO4 reversed activation by the chaotropic salt CaCl2 and to a lesser extent reversed activation by sublethal heat (75 degrees C) or urea. Most treatments that enhanced activation increased spore injury at higher temperatures, which resulted in decreased germination. However, (NH4)2SO4 and a decrease in pH from 5.6 to 3.8, which inhibited activation, also favored injury. The results suggest that activation involves a conformational change of a spore protein(s) through weakening of hydrophobic molecular forces and that activation and injury occur at different spore sites.

Germination of spores from Clostridium botulinum B-aphis and Ba410

The germination of spores from Clostridium botulinum B-aphis and Ba410 was examined. In a complex medium, heat activation of spores from both strains doubled the germination rates and was required for germination in the presence of 2% NaCl. In a defined medium (CTB [D. B. Rowley and F. Feeherry, J. Bacteriol. 104:1151-1157, 1970]), the parent strain B-aphis germinated at a rate of 0.77% min-1 in the absence of NaCl and was not affected by 2% NaCl. A salt-tolerant derivative, strain Ba410, germinated at rates of 0.16% min-1 in CTB and 0.04% min-1 in CTB containing 2% NaCl. L-Alanine-triggered spores germinated faster than did L-cysteine-triggered spores from both strains. When both amino acids were present, B-aphis germinated rapidly in the absence of NaCl and had biphasic kinetics in the presence of NaCl. Strain Ba410 had biphasic kinetics in the absence of NaCl and germinated slowly with single-phase kinetics in the presence of NaCl. L-Alanine- and L-cysteine-triggered germinations were each inhibited by both D-alanine and D-cysteine, indicating a common germinant-binding site for both alanine and cysteine. Attempts to select for variants with amino acid-specific germinant-binding sites were unsuccessful. Differences in the germination kinetics of both strains could not be explained by ultrastructural differences. Transmission electron micrographs revealed striking similarities between the strains.

Inhibition of germinant binding by bacterial spores in acidic environments

Commitment to germinate occurred in both Clostridium botulinum and Bacillus cereus spores during 0.5 min of exposure to 100 mM L-alanine or L-cysteine, measured by the inability of germination inhibitors (D form of amino acid) to inhibit germination. Spore germination at pH 4.5 was inhibited because the germinant did not bind to the trigger sites. C. botulinum spores exposed to 100 mM L-alanine or L-cysteine at pH 4.5 remained sensitive to D-amino acid inhibition at pH 7, indicating that no germinants had bound to the trigger site at pH 4.5. Inhibition of germinant binding at pH 4.5 was reversible but lagged in commitment to germinate upon transfer to pH 7. Spores sequentially exposed to pH 4.5 buffer and pH 7 buffer with the germinant also demonstrated a lag in commitment to germinate. The pH at which binding was inhibited was not significantly affected by composition of the buffer or by reduced germinant concentrations (10 mM). Nonspecific uptake of L-[3H]alanine by C. botulinum spores was not inhibited at pH 4.5. Inhibition of germinant binding in acidic environments appeared to be due to protonation of a functional group in or near the trigger site. This may represent a general mechanism for inhibition of spore germination in acidic environments.

Resistance, germination, and permeability correlates of Bacillus megaterium spores successively divested of integument layers

A variant strain that produced spores lacking exosporium was isolated from a culture of Bacillus megaterium QM-B1551. Two additional spore morphotypes were obtained from the parent and variant strains by chemical removal of the complex of coat and outer membrane. Among the four morphotype spores, heat resistance did not correlate with total water content, wet density, refractive index, or dipicolinate or cation content, but did correlate with the volume ratio of protoplast to protoplast plus cortex. The divestment of integument layers exterior to the cortex had little influence on heat resistance. Moreover, the divestment did not change the response of either the parent or the variant spores to various germination-initiating agents, except for making the spores susceptible to germination by lysozyme. The primary permeability barrier to glucose for the intact parent and variant spores was found to be the outer membrane, whereas the barrier for the divested spores was the inner membrane.

Proposed mechanism for sensitization by hypochlorite treatment of Clostridium botulinum spores

Hypochlorite-treated Clostridium botulinum 12885A spores, but not buffer-treated spores, could be germinated with lysozyme, indicating that their coats are made permeable to lysozyme by hypochlorite treatment so that the cortex is accessible. Hypochlorite-treated spores and spores extracted with 8 M urea-2-mercaptoethanol (pH 3.0) were sensitive to certain components of recovery media, but spores sensitized to lysozyme by other treatments were not. These data indicate that hypochlorite does more than increase coat permeability to lysozyme. Scanning electron microscopy revealed a more open-appearing surface of hypochlorite-treated spores, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that a greater amount of protein was removed from hypochlorite-treated and other lysozyme-sensitized spores than from buffer-treated spores. The data suggest that spore coat proteins may be removed by hypochlorite treatment, and this may be responsible for the sensitivity of spores and for their observed ability to germinate in lysozyme.