Role of small, acid-soluble spore proteins in the resistance of Clostridium perfringens spores to chemicals

Isolation of a Virulent Clostridium perfringens Strain from Elaphurus davidianus and Characterization by Whole-Genome Sequence Analysis

Clostridium perfringens (C. perfringens) is an important veterinary pathogen and a noteworthy threat to human and animal health. Recently, there has been a significant rise in the number of moose fatalities caused by this rare, endemic species in China. Currently, there is an increasing trend in conducting whole-genome analysis of C. perfringens strains originating from pigs and chickens, whereas fewer studies have been undertaken on Elaphurus davidianus-originating strains at the whole-genome level. Our laboratory has identified and isolated five C. perfringens type A from affected Elaphurus davidianus. The current study identified the most potent strain of C. perfringens, which originated from Elaphurus davidianus, and sequenced its genome to reveal virulence genes and pathogenicity. Our findings show that strain CX1-4 exhibits the highest levels of phospholipase activity, hemolytic activity, and mouse toxicity compared to the other four isolated C. perfringens type A strains. The chromosome sequence length of the CX1-4 strain was found to be 3,355,389 bp by complete genome sequencing. The current study unveils the genomic characteristics of C. perfringens type A originating from Elaphurus davidianus. It provides a core foundation for further investigation regarding the prevention and treatment of such infectious diseases in Elaphurus davidianus.

The small acid-soluble proteins of spore-forming organisms: similarities and differences in function

The small acid-soluble proteins are found in all endospore-forming organisms and are a major component of spores. Through their DNA binding capabilities, the SASPs shield the DNA from outside insults (e.g., UV and genotoxic chemicals). The absence of the major SASPs results in spores with reduced viability when exposed to UV light and, in at least one case, the inability to complete sporulation. While the SASPs have been characterized for decades, some evidence suggests that using newer technologies to revisit the roles of the SASPs could reveal novel functions in spore regulation.

Effects of sporulation conditions on the growth, germination, and resistance of Clostridium perfringens spores

Clostridium perfringens can form metabolically dormant spores that can survive in meat preservation processes and cause food spoilage and human disease upon germination and outgrowth. The characteristics of spores in food products are closely related to the sporulation environment. To control or inactivate C. perfringens spores in food industry, the effects of sporulation conditions on the spores characteristics should be examined. This study aimed to investigate the effects of temperature (T), pH, and water activity (a_w) on the growth, germination, and wet-heat resistance of C. perfringens C1 spores isolated from food product. The results showed that C. perfringens C1 spores produced at T = 37 °C, pH = 8, and a_w = 0.997 had the highest sporulation rate and germination efficiency and lowest wet-heat resistance. A further increase in pH and sporulation temperature reduced the spore counts and germination efficiency, but enhanced spores' wet-heat resistance. By using air-drying method and Raman spectroscopy analysis, the water content, composition, and levels of calcium dipicolinic acid, proteins, and nucleic acids in spores produced under different sporulation conditions were determined. The results obtained revealed that sporulation conditions should be carefully considered during food production and processing, thus providing a novel insight into prevention and control of spores in food industry.

Inactivation of Clostridium perfringens C1 Spores by the Combination of Mild Heat and Lactic Acid

Clostridium perfringens is a major pathogen causing foodborne illnesses. In this experiment, the inactivation effects of heat and lactic acid (LA) treatments on C. perfringens spores was investigated. Heat treatment (80 °C, 90 °C and 100 °C), LA (0.5% and 1%), and combined LA and heat treatments for 30 and 60 min were performed. Residual spore counts showed that the count of C. perfringens spores was below the detection limit within 30 min of treatment with 1% LA and heat treatment at 90 °C. Scanning electron microscopy and confocal scanning laser microscopy results showed that the surface morphology of the spores was severely disrupted by the co-treatment. The particle size of the spores was reduced to 202 nm and the zeta potential to −3.66 mv. The inner core of the spores was disrupted and the co-treatment resulted in the release of 77% of the nuclear contents 2,6-pyridinedicarboxylic acid. In addition, the hydrophobicity of spores was as low as 11% after co-treatment with LA relative to the control, indicating that the outer layer of spores was severely disrupted. Thus, synergistic heating and LA treatment were effective in inactivating C. perfringens spores.

Small Prokaryotic DNA-Binding Proteins Protect Genome Integrity throughout the Life Cycle

Genomes of all organisms are persistently threatened by endogenous and exogenous assaults. Bacterial mechanisms of genome maintenance must provide protection throughout the physiologically distinct phases of the life cycle. Spore-forming bacteria must also maintain genome integrity within the dormant endospore. The nucleoid-associated proteins (NAPs) influence nucleoid organization and may alter DNA topology to protect DNA or to alter gene expression patterns. NAPs are characteristically multifunctional; nevertheless, Dps, HU and CbpA are most strongly associated with DNA protection. Archaea display great variety in genome organization and many inhabit extreme environments. As of yet, only MC1, an archaeal NAP, has been shown to protect DNA against thermal denaturation and radiolysis. ssDNA are intermediates in vital cellular processes, such as DNA replication and recombination. Single-stranded binding proteins (SSBs) prevent the formation of secondary structures but also protect the hypersensitive ssDNA against chemical and nuclease degradation. Ionizing radiation upregulates SSBs in the extremophile Deinococcus radiodurans.

Insights into the Structure and Protein Composition of Moorella thermoacetica Spores Formed at Different Temperatures

The bacterium Moorella thermoacetica produces the most heat-resistant spores of any spoilage-causing microorganism known in the food industry. Previous work by our group revealed that the resistance of these spores to wet heat and biocides was lower when spores were produced at a lower temperature than the optimal temperature. Here, we used electron microcopy to characterize the ultrastructure of the coat of the spores formed at different sporulation temperatures; we found that spores produced at 55 °C mainly exhibited a lamellar inner coat tightly associated with a diffuse outer coat, while spores produced at 45 °C showed an inner and an outer coat separated by a less electron-dense zone. Moreover, misarranged coat structures were more frequently observed when spores were produced at the lower temperature. We then analyzed the proteome of the spores obtained at either 45 °C or 55 °C with respect to proteins putatively involved in the spore coat, exosporium, or in spore resistance. Some putative spore coat proteins, such as CotSA, were only identified in spores produced at 55 °C; other putative exosporium and coat proteins were significantly less abundant in spores produced at 45 °C. Altogether, our results suggest that sporulation temperature affects the structure and protein composition of M. thermoacetica spores.

The small acid-soluble proteins of Clostridioides difficile are important for UV resistance and serve as a check point for sporulation

Clostridioides difficile is a nosocomial pathogen which causes severe diarrhea and colonic inflammation. C. difficile causes disease in susceptible patients when endospores germinate into the toxin-producing vegetative form. The action of these toxins results in diarrhea and the spread of spores into the hospital and healthcare environments. Thus, the destruction of spores is imperative to prevent disease transmission between patients. However, spores are resilient and survive extreme temperatures, chemical exposure, and UV treatment. This makes their elimination from the environment difficult and perpetuates their spread between patients. In the model spore-forming organism, Bacillus subtilis, the small acid-soluble proteins (SASPs) contribute to these resistances. The SASPs are a family of small proteins found in all endospore-forming organisms, C. difficile included. Although these proteins have high sequence similarity between organisms, the role(s) of the proteins differ. Here, we investigated the role of the main α/β SASPs, SspA and SspB, and two annotated putative SASPs, CDR20291_1130 and CDR20291_3080, in protecting C. difficile spores from environmental insults. We found that SspA is necessary for conferring spore UV resistance, SspB minorly contributes, and the annotated putative SASPs do not contribute to UV resistance. In addition, the SASPs minorly contribute to the resistance of nitrous acid. Surprisingly, the combined deletion of sspA and sspB prevented spore formation. Overall, our data indicate that UV resistance of C. difficile spores is dependent on SspA and that SspA and SspB regulate/serve as a checkpoint for spore formation, a previously unreported function of SASPs.

Comparative Genome Analysis and Phenotypic Characterization of Clostridium gasigenes CGAS001 Isolated From Chilled Vacuum-Packed Lamb Meat

Genomic data for psychrophilic bacteria causing blown pack spoilage (BPS) are limited. This study characterizes the genome of a novel Clostridium gasigenes strain CGAS001 isolated from meat juice sample (MJS) of vacuum-packed lamb meat by comparing it with the type strain C. gasigenes DSM 12272 and five strains representing four other BPS-causing Clostridium sensu stricto species. Phenotypic characteristics of the strain, which include biochemical characteristics, antimicrobial resistance and production of putative polyketide, have been determined. The size of its draft genome is 4.1 Mb with 3,845 coding sequences, 28.7% GC content and 95 RNA genes that include 75 tRNAs, 17 rRNAs, and 3 ncRNAs. Average Nucleotide Identity (ANI) and digital DNA-DNA Hybridization (dDDH) predict that C. gasigenes CGAS001 and DSM 12272 constitute a single species (ANI and dDDH = 98.3% for speciation) but two distinct subspecies (dDDH = 73.3% for subspeciation). The genome is characterized by saccharolytic, lipolytic and proteolytic genes as well as hemolysins and phospholipases, which are consistent with its phenotype. The genome also reveals the ability of C. gasigenes to synthesize polyketides which is demonstrated by the antimicrobial activity of a crude polyketide extract against Listeria monocytogenes and Enterococcus devriesei. The strain is resistant to polymyxin B and streptomycin. The genetic and phenotypic analyses suggest that CGAS001 constitutes a novel subspecies of C. gasigenes adapted to a saprophytic lifestyle and can synthesize narrow spectrum antimicrobial compounds.

Near-infrared spectroscopy coupled with chemometrics algorithms for the quantitative determination of the germinability of Clostridium perfringens in four different matrices

Clostridium perfringens (C. perfringens) has the ability to form metabolically-dormant spores that can survive food preservation processes and cause food spoilage and foodborne safety risks upon germination outgrowth. This study was conducted to investigate the effects of different AGFK concentrations (0, 50, 100, 200 mM/mL) on the spore germination of C. perfringens in four matrices, including Tris-HCl, FTG, milk, and chicken soup. C. perfringens spore germinability was investigated using near infrared spectroscopy (NIRS) combined with chemometrics. The spore germination rate (S), the OD₆₀₀%, and the Ca²⁺-DPA% were measured using traditional spore germination methods. The results of spore germination assays showed that the optimum germination rate was obtained using 100 mM/L concentrations of AGFK in the FTG medium, and the S, OD₆₀₀% and Ca²⁺-DPA% were 98.6%, 59.3% and 95%, respectively. The best prediction models for the S, OD₆₀₀% and Ca²⁺-DPA% were obtained using SNV as the preprocessing method for the original spectra, with the competitive adaptive weighted resampling method (CARS) as the characteristic variables related to the selected spore germination methods from NIRS data. The results of the S showed that the optimum model was built by CARS-PLSR (RMSEV = 0.745, R_c = 0.897, RMSEP = 0.769, R_p = 0.883). For the OD₆₀₀%, interval partial least squares regression (CARS-siPLS) was performed to optimize the models. The calibration yielded acceptable results (RMSEV = 0.218, R_c = 0.879, RMSEP = 0.257, R_p = 0.845). For the Ca²⁺-DPA%, the optimum model with CARS-siPLS yielded acceptable results (RMSEV = 44.7, R_c = 0.883, RMSEP = 50.2, R_p = 0.872). This indicated that quantitative determinations of the germinability of C. perfringens spores using NIR technology is feasible. A new method based on NIR was provided for rapid, automatic, and non-destructive determination of the germinability of C. perfringens spores.

The serine proteases CspA and CspC are essential for germination of spores of Clostridium perfringens SM101 through activating SleC and cortex hydrolysis

Clostridium perfringens SM101 genome encodes three serine proteases (CspA, CspB, and CspC), and genetic evidence indicates that CspB is required for processing of pro-SleC into active SleC, an enzyme essential for degradation of the peptidoglycan cortex during spore germination. In this study, the expression of cspA and cspC, as well as the germination and colony formation by spores of cspAC and cspC mutants of strain SM101, were assessed. We demonstrated that 1) the cspA and cspC genes were expressed as a bicistronic operon only during sporulation in the mother cell compartment of SM101; 2) both cspAC and cspC mutant spores were unable to germinate significantly with either KCl, l-glutamine, brain heart infusion (BHI) broth, or a 1:1 chelate of Ca²⁺ and dipicolinic acid (DPA); 3) consistent with germination results, both cspAC and cspC mutant spores were defective in normal DPA release; 4) the colony formation by cspAC and cspC mutant spores was ~10⁶-fold lower than that of wild-type spores, although decoated mutant spores yielded wild-type level colony formation on plates containing lysozyme; 5) no processing of inactive pro-SleC into active SleC was observed in cspAC and cspC mutant spores during germination; and finally, 6) the defects in germination, DPA release, colony formation and SleC processing in cspAC and cspC mutant spores were complemented by the wild-type cspA-cspC operon. Collectively, these results indicate that both CspA and CspC are essential for C. perfringens spore germination through activating SleC and inducing cortex hydrolysis.

Freezing Tolerance of Thermophilic Bacterial Endospores in Marine Sediments

Dormant endospores of anaerobic, thermophilic bacteria found in cold marine sediments offer a useful model for studying microbial biogeography, dispersal, and survival. The dormant endospore phenotype confers resistance to unfavorable environmental conditions, allowing dispersal to be isolated and studied independently of other factors such as environmental selection. To study the resilience of thermospores to conditions relevant for survival in extreme cold conditions, their viability following different freezing treatments was tested. Marine sediment was frozen at either −80°C or −20°C for 10 days prior to pasteurization and incubation at +50°C for 21 days to assess thermospore viability. Sulfate reduction commenced at +50°C following both freezing pretreatments indicating persistence of thermophilic endospores of sulfate-reducing bacteria. The onset of sulfate reduction at +50°C was delayed in −80°C pretreated microcosms, which exhibited more variability between triplicates, compared to −20°C pretreated microcosms and parallel controls that were not frozen in advance. Microbial communities were evaluated by 16S rRNA gene amplicon sequencing, revealing an increase in the relative sequence abundance of thermophilic endospore-forming Firmicutes in all microcosms. Different freezing pretreatments (−80°C and −20°C) did not appreciably influence the shift in overall bacterial community composition that occurred during the +50°C incubations. Communities that had been frozen prior to +50°C incubation showed an increase in the relative sequence abundance of operational taxonomic units (OTUs) affiliated with the class Bacilli, relative to unfrozen controls. These results show that freezing impacts but does not obliterate thermospore populations and their ability to germinate and grow under appropriate conditions. Indeed the majority of the thermospore OTUs detected in this study (21 of 22) could be observed following one or both freezing treatments. These results are important for assessing thermospore viability in frozen samples and following cold exposure such as the very low temperatures that would be encountered during panspermia.

Observations on research with spores of Bacillales and Clostridiales species

The purpose of this article is to highlight some areas of research with spores of bacteria of Firmicute species in which the methodology too commonly used is not optimal and generates misleading results. As a consequence, conclusions drawn from data obtained are often flawed or not appropriate. Topics covered in the article include the following: (i) the importance of using well-purified bacterial spores in studies on spore resistance, composition, killing, disinfection and germination; (ii) methods for obtaining good purification of spores of various species; (iii) appropriate experimental approaches to determine mechanisms of spore resistance and spore killing by a variety of agents, as well as known mechanisms of spore resistance and killing; (iv) common errors made in drawing conclusions about spore killing by various agents, including failure to neutralize chemical agents before plating for viable spore enumeration, and equating correlations between changes in spore properties accompanying spore killing with causation. It is hoped that a consideration of these topics will improve the quality of spore research going forward.

First report of two complete Clostridium chauvoei genome sequences and detailed in silico genome analysis

Clostridium (C.) chauvoei is a Gram-positive, spore forming, anaerobic bacterium. It causes black leg in ruminants, a typically fatal histotoxic myonecrosis. High quality circular genome sequences were generated for the C. chauvoei type strain DSM 7528^T (ATCC 10092^T) and a field strain 12S0467 isolated in Germany. The origin of replication (oriC) was comparable to that of Bacillus subtilis in structure with two regions containing DnaA boxes. Similar prophages were identified in the genomes of both C. chauvoei strains which also harbored hemolysin and bacterial spore formation genes. A CRISPR type I-B system with limited variations in the repeat number was identified. Sporulation and germination process related genes were homologous to that of the Clostridia cluster I group but novel variations for regulatory genes were identified indicative for strain specific control of regulatory events. Phylogenomics showed a higher relatedness to C. septicum than to other so far sequenced genomes of species belonging to the genus Clostridium. Comparative genome analysis of three C. chauvoei circular genome sequences revealed the presence of few inversions and translocations in locally collinear blocks (LCBs). The species genome also shows a large number of genes involved in proteolysis, genes for glycosyl hydrolases and metal iron transportation genes which are presumably involved in virulence and survival in the host. Three conserved flagellar genes (fliC) were identified in each of the circular genomes. In conclusion this is the first comparative analysis of circular genomes for the species C. chauvoei, enabling insights into genome composition and virulence factor variation.

The role of small acid-soluble proteins (SASPs) in protection of spores of Clostridium botulinum against nitrous acid

Mutant strains of Clostridium botulinum ATCC 3502 were generated using the ClosTron in four genes (CBO1789, CBO1790, CBO3048, CBO3145) identified as encoding α/β-type SASP homologues. The spores of mutant strains in which CBO1789 or CBO1790 was inactivated demonstrated a significant increase in sensitivity to the damaging agent nitrous acid (P<0.01), a phenotype that was partially restored to wild-type in complementation studies. In contrast to nitrous acid, the spores of the CBO1789 and CBO1790 mutants showed no change in their resistance to formaldehyde and hydrogen peroxide (P>0.05), two other chemicals commonly used as components of disinfection regimes. These data indicate that the SASPs CBO1789 or CBO1790 play a significant role in resistance to nitrous acid, but not in resistance to formaldehyde or hydrogen peroxide.

Location and stoichiometry of the protease CspB and the cortex-lytic enzyme SleC in Clostridium perfringens spores

The protease CspB and the cortex-lytic enzyme SleC are essential for peptoglycan cortex hydrolysis during germination of spores of the Clostridium perfringens food poisoning isolate SM101. In this study, Western blot analyses were used to demonstrate that CspB and SleC are present exclusively in the C. perfringens SM101 spore coat layer fraction and absent in the lysate from decoated spores and from the purified inner spore membrane. These results indicate why decoating treatments greatly reduce both germination and apparent viability of C. perfringens spores in the absence of an exogenous lytic enzyme. In addition, quantitative Western blot analyses showed that there are approximately 2000 and 130,000 molecules of CspB and pro-SleC, respectively, per C. perfringens SM101 spore, consistent with CspB's role in acting catalytically on pro-SleC to convert this zymogen to the active enzyme.

The inhibitory effects of sorbate and benzoate against Clostridium perfringens type A isolates

This study evaluated the inhibitory effects of sorbate and benzoate against Clostridium perfringens type A food poisoning (FP) and non-food-borne (NFB) disease isolates. No significant inhibition of germination of spores of both FP and NFB isolates was observed in rich medium (pH 7.0) supplemented with permissive level of sodium sorbate (0.3% ≈ 0.13 mM undissociated sorbic acid) or sodium benzoate (0.1% ≈ 0.01 mM undissociated benzoic acid) used in foods. However, these levels of sorbate and benzoate effectively arrested outgrowth of germinated C. perfringens spores in rich medium. Lowering the pH of the medium increases the inhibitory effects of sorbate and benzoate against germination of spores of NFB isolates, and outgrowth of spores of both FP and NFB isolates. Furthermore, sorbate and benzoate inhibited vegetative growth of C. perfringens isolates. However, the permissible levels of these organic salts could not control the growth of C. perfringens spores in chicken meat stored under extremely abusive conditions. In summary, although sorbate and benzoate showed inhibitory activities against C. perfringens in the rich medium, no such effect was observed in cooked chicken meat. Therefore, caution should be taken when applying these organic salts into meat products to reduce or eliminate C. perfringens spores.

Clostridium difficile spores: a major threat to the hospital environment

Clostridium difficile is a Gram-positive, anaerobic spore former and is an important nosocomial and community-acquired pathogenic bacterium. C. difficile infections (CDI) are a leading cause of infections worldwide with elevated rates of morbidity. Despite the fact that two major virulence factors, the enterotoxin TcdA and the cytotoxin TcdB, are essential in the development of CDI, C. difficile spores are the main vehicle of infection, and persistence and transmission of CDI and are thought to play an essential role in episodes of CDI recurrence and horizontal transmission. Recent research has unmasked several properties of C. difficile's unique strategy to form highly transmissible spores and to persist in the colonic environment. Therefore, the aim of this article is to summarize recent advances in the biological properties of C. difficile spores, which might be clinically relevant to improve the management of CDI in hospital environments.

Physiology and Sporulation in Clostridium

Clostridia are Gram-positive, anaerobic, endospore-forming bacteria, incapable of dissimilatory sulfate reduction. Comprising approximately 180 species, the genus Clostridium is one of the largest bacterial genera. Physiology is mostly devoted to acid production. Numerous pathways are known, such as the homoacetate fermentation by acetogens, the propionate fermentation by Clostridium propionicum , and the butyrate/butanol fermentation by C. acetobutylicum , a well-known solvent producer. Clostridia degrade sugars, alcohols, amino acids, purines, pyrimidines, and polymers such as starch and cellulose. Energy conservation can be performed by substrate-level phosphorylation as well as by the generation of ion gradients. Endospore formation resembles the mechanism elucidated in Bacillus . Morphology, contents, and properties of spores are very similar to bacilli endospores. Sporulating clostridia usually form swollen mother cells and accumulate the storage substance granulose. However, clostridial sporulation differs by not employing the so-called phosphorelay. Initiation starts by direct phosphorylation of the master regulator Spo0A. The cascade of sporulation-specific sigma factors is again identical to what is known from Bacillus . The onset of sporulation is coupled in some species to either solvent (acetone, butanol) or toxin (e.g., C. perfringens enterotoxin) formation. The germination of spores is often induced by various amino acids, often in combination with phosphate and sodium ions. In medical applications, C. butyricum spores are used as a C. difficile prophylaxis and as treatment against diarrhea. Recombinant spores are currently under investigation and testing as antitumor agents, because they germinate only in hypoxic tissues (i.e., tumor tissue), allowing precise targeting and direct killing of tumor cells.

Clostridium difficile spore-macrophage interactions: spore survival

BACKGROUND

Clostridium difficile is the main cause of nosocomial infections including antibiotic associated diarrhea, pseudomembranous colitis and toxic megacolon. During the course of Clostridium difficile infections (CDI), C. difficile undergoes sporulation and releases spores to the colonic environment. The elevated relapse rates of CDI suggest that C. difficile spores has a mechanism(s) to efficiently persist in the host colonic environment.

METHODOLOGY/PRINCIPAL FINDINGS

In this work, we provide evidence that C. difficile spores are well suited to survive the host's innate immune system. Electron microscopy results show that C. difficile spores are recognized by discrete patchy regions on the surface of macrophage Raw 264.7 cells, and phagocytosis was actin polymerization dependent. Fluorescence microscopy results show that >80% of Raw 264.7 cells had at least one C. difficile spore adhered, and that ∼60% of C. difficile spores were phagocytosed by Raw 264.7 cells. Strikingly, presence of complement decreased Raw 264.7 cells' ability to phagocytose C. difficile spores. Due to the ability of C. difficile spores to remain dormant inside Raw 264.7 cells, they were able to survive up to 72 h of macrophage infection. Interestingly, transmission electron micrographs showed interactions between the surface proteins of C. difficile spores and the phagosome membrane of Raw 264.7 cells. In addition, infection of Raw 264.7 cells with C. difficile spores for 48 h produced significant Raw 264.7 cell death as demonstrated by trypan blue assay, and nuclei staining by ethidium homodimer-1.

CONCLUSIONS/SIGNIFICANCE

These results demonstrate that despite efficient recognition and phagocytosis of C. difficile spores by Raw 264.7 cells, spores remain dormant and are able to survive and produce cytotoxic effects on Raw 264.7 cells.

Bacterial spore structures and their protective role in biocide resistance

The structure and chemical composition of bacterial spores differ considerably from those of vegetative cells. These differences largely account for the unique resistance properties of the spore to environmental stresses, including disinfectants and sterilants, resulting in the emergence of spore-forming bacteria such as Clostridium difficile as major hospital pathogens. Although there has been considerable work investigating the mechanisms of action of many sporicidal biocides against Bacillus subtilis spores, there is far less information available for other species and particularly for various Clostridia. This paucity of information represents a major gap in our knowledge given the importance of Clostridia as human pathogens. This review considers the main spore structures, highlighting their relevance to spore resistance properties and detailing their chemical composition, with a particular emphasis on the differences between various spore formers. Such information will be vital for the rational design and development of novel sporicidal chemistries with enhanced activity in the future.

Strategy to inactivate Clostridium perfringens spores in meat products

The current study aimed to develop an inactivation strategy for Clostridium perfringens spores in meat through a combination of spore activation at low pressure (100-200 MPa, 7 min) and elevated temperature (80 degrees C, 10 min); spore germination at high temperatures (55, 60 or 65 degrees C); and inactivation of germinated spores with elevated temperatures (80 and 90 degrees C, 10 and 20 min) and high pressure (586 MPa, at 23 and 73 degrees C, 10 min). Low pressures (100-200 MPa) were insufficient to efficiently activate C. perfringens spores for germination. However, C. perfringens spores were efficiently activated with elevated temperature (80 degrees C, 10 min), and germinated at temperatures lethal for vegetative cells (>or= 55 degrees C) when incubated for 60 min with a mixture of L-asparagine and KCl (AK) in phosphate buffer (pH 7) and in poultry meat. Inactivation of spores (approximately 4 decimal reduction) in meat by elevated temperatures (80-90 degrees C for 20 min) required a long germination period (55 degrees C for 60 min). However, similar inactivation level was reached with shorter germination period (55 degrees C for 15 min) when spore contaminated-meat was treated with pressure-assisted thermal processing (568 MPa, 73 degrees C, 10 min). Therefore, the most efficient strategy to inactivate C. perfringens spores in poultry meat containing 50 mM AK consisted: (i) a primary heat treatment (80 degrees C, 10 min) to pasteurize and denature the meat proteins and to activate C. perfringens spores for germination; (ii) cooling of the product to 55 degrees C in about 20 min and further incubation at 55 degrees C for about 15 min for spore germination; and (iii) inactivation of germinated spores by pressure-assisted thermal processing (586 MPa at 73 degrees C for 10 min). Collectively, this study demonstrates the feasibility of an alternative and novel strategy to inactivate C. perfringens spores in meat products formulated with germinants specific for C. perfringens.

Characterization of Clostridium perfringens spores that lack SpoVA proteins and dipicolinic acid

Spores of Clostridium perfringens possess high heat resistance, and when these spores germinate and return to active growth, they can cause gastrointestinal disease. Work with Bacillus subtilis has shown that the spore's dipicolinic acid (DPA) level can markedly influence both spore germination and resistance and that the proteins encoded by the spoVA operon are essential for DPA uptake by the developing spore during sporulation. We now find that proteins encoded by the spoVA operon are also essential for the uptake of Ca(2+) and DPA into the developing spore during C. perfringens sporulation. Spores of a spoVA mutant had little, if any, Ca(2+) and DPA, and their core water content was approximately twofold higher than that of wild-type spores. These DPA-less spores did not germinate spontaneously, as DPA-less B. subtilis spores do. Indeed, wild-type and spoVA C. perfringens spores germinated similarly with a mixture of l-asparagine and KCl (AK), KCl alone, or a 1:1 chelate of Ca(2+) and DPA (Ca-DPA). However, the viability of C. perfringens spoVA spores was 20-fold lower than the viability of wild-type spores. Decoated wild-type and spoVA spores exhibited little, if any, germination with AK, KCl, or exogenous Ca-DPA, and their colony-forming efficiency was 10(3)- to 10(4)-fold lower than that of intact spores. However, lysozyme treatment rescued these decoated spores. Although the levels of DNA-protective alpha/beta-type, small, acid-soluble spore proteins in spoVA spores were similar to those in wild-type spores, spoVA spores exhibited markedly lower resistance to moist heat, formaldehyde, HCl, hydrogen peroxide, nitrous acid, and UV radiation than wild-type spores did. In sum, these results suggest the following. (i) SpoVA proteins are essential for Ca-DPA uptake by developing spores during C. perfringens sporulation. (ii) SpoVA proteins and Ca-DPA release are not required for C. perfringens spore germination. (iii) A low spore core water content is essential for full resistance of C. perfringens spores to moist heat, UV radiation, and chemicals.

A novel small acid soluble protein variant is important for spore resistance of most Clostridium perfringens food poisoning isolates

Clostridium perfringens is a major cause of food poisoning (FP) in developed countries. C. perfringens isolates usually induce the gastrointestinal symptoms of this FP by producing an enterotoxin that is encoded by a chromosomal (cpe) gene. Those typical FP strains also produce spores that are extremely resistant to food preservation approaches such as heating and chemical preservatives. This resistance favors their survival and subsequent germination in improperly cooked, prepared, or stored foods. The current study identified a novel α/β-type small acid soluble protein, now named Ssp4, and showed that sporulating cultures of FP isolates producing resistant spores consistently express a variant Ssp4 with an Asp substitution at residue 36. In contrast, Gly was detected at Ssp4 residue 36 in C. perfringens strains producing sensitive spores. Studies with isogenic mutants and complementing strains demonstrated the importance of the Asp 36 Ssp4 variant for the exceptional heat and sodium nitrite resistance of spores made by most FP strains carrying a chromosomal cpe gene. Electrophoretic mobility shift assays and DNA binding studies showed that Ssp4 variants with an Asp at residue 36 bind more efficiently and tightly to DNA than do Ssp4 variants with Gly at residue 36. Besides suggesting one possible mechanistic explanation for the highly resistant spore phenotype of most FP strains carrying a chromosomal cpe gene, these findings may facilitate eventual development of targeted strategies to increase killing of the resistant spores in foods. They also provide the first indication that SASP variants can be important contributors to intra-species (and perhaps inter-species) variations in bacterial spore resistance phenotypes. Finally, Ssp4 may contribute to spore resistance properties throughout the genus Clostridium since ssp4 genes also exist in the genomes of other clostridial species.

Spores made by pathogenic Bacillus and Clostridium spp. contribute to disease transmission. Clostridium perfringens food poisoning (FP) isolates typically produce spores with exceptional resistance to heat and sodium nitrite. This spore resistance probably facilitates FP strain survival in improperly cooked/held foods, contributing to C. perfringens FP outbreaks, which rank among the most common food-borne diseases in developed countries. Currently, the mechanistic basis of the resistant spore phenotype of FP strains is unknown. Here, we report the identification of a novel small acid soluble protein, named Ssp4, and show that sporulating cultures of FP strains producing resistant spores express an Ssp4 variant with Asp at residue 36, while sporulating cultures of C. perfringens strains producing sensitive spores express an Ssp4 with Gly at residue 36. We now demonstrate that i) the Ssp4 Asp variant is required for extreme spore resistance of FP strains and ii) this protein may help protect FP strains via tighter DNA binding than the Ssp4 Gly variant. Our study provides important insights into the transmission of a common FP agent and may suggest strategies to interfere with resistant spores of FP strains. These findings may also have relevance for other pathogenic Clostridium spp. carrying an ssp4 gene.

Roles of DacB and spm proteins in clostridium perfringens spore resistance to moist heat, chemicals, and UV radiation

Clostridium perfringens food poisoning is caused mainly by enterotoxigenic type A isolates that typically possess high spore heat resistance. Previous studies have shown that alpha/beta-type small, acid-soluble proteins (SASP) play a major role in the resistance of Bacillus subtilis and C. perfringens spores to moist heat, UV radiation, and some chemicals. Additional major factors in B. subtilis spore resistance are the spore's core water content and cortex peptidoglycan (PG) structure, with the latter properties modulated by the spm and dacB gene products and the sporulation temperature. In the current work, we have shown that the spm and dacB genes are expressed only during C. perfringens sporulation and have examined the effects of spm and dacB mutations and sporulation temperature on spore core water content and spore resistance to moist heat, UV radiation, and a number of chemicals. The results of these analyses indicate that for C. perfringens SM101 (i) core water content and, probably, cortex PG structure have little if any role in spore resistance to UV and formaldehyde, presumably because these spores' DNA is saturated with alpha/beta-type SASP; (ii) spore resistance to moist heat and nitrous acid is determined to a large extent by core water content and, probably, cortex structure; (iii) core water content and cortex PG cross-linking play little or no role in spore resistance to hydrogen peroxide; (iv) spore core water content decreases with higher sporulation temperatures, resulting in spores that are more resistant to moist heat; and (v) factors in addition to SpmAB, DacB, and sporulation temperature play roles in determining spore core water content and thus, spore resistance to moist heat.