Early events during bacterial endospore formation

Moist-heat resistance, spore aging, and superdormancy in Clostridium difficile

Clostridium difficile spores can survive extended heating at 71°C (160°F), a minimum temperature commonly recommended for adequate cooking of meats. To determine the extent to which higher temperatures would be more effective at killing C. difficile, we quantified (D values) the effect of moist heat at 85°C (145°F, for 0 to 30 min) on C. difficile spores and compared it to the effects at 71 and 63°C. Fresh (1-week-old) and aged (≥20-week-old) C. difficile spores from food and food animals were tested in multiple experiments. Heating at 85°C markedly reduced spore recovery in all experiments (5 to 6 log(10) within 15 min of heating; P < 0.001), regardless of spore age. In ground beef, the inhibitory effect of 85°C was also reproducible (P < 0.001), but heating at 96°C reduced 6 log(10) within 1 to 2 min. Mechanistically, optical density and enumeration experiments indicated that 85°C inhibits cell division but not germination, but the inhibitory effect was reversible in some spores. Heating at 63°C reduced counts for fresh spores (1 log(10), 30 min; P < 0.04) but increased counts of 20-week-old spores by 30% (15 min; P < 0.02), indicating that sublethal heat treatment reactivates superdormant spores. Superdormancy is an increasingly recognized characteristic in Bacillus spp., and it is likely to occur in C. difficile as spores age. The potential for reactivation of (super)dormant spores with sublethal temperatures may be a food safety concern, but it also has potential diagnostic value. Ensuring that food is heated to >85°C would be a simple and important intervention to reduce the risk of inadvertent ingestion of C. difficile spores.

Intergenic suppression of spoO phenotypes by the Bacillus subtilis mutation rvtA

A collection of intergenic suppressors of the Bacillus subtilis spoOF221 mutation has been isolated. One of these suppressors, rvtA, has been mapped between lys-1and aroD. The rvtA suppressor restores spoOF sporulation to wild type levels and substantially improves the sporulation efficiencies of spoOB and spoOE strains. The rvtA gene does not affect the Spo phenotype of spoOH, spoOJ or spoOK mutants. The rvtA gene also prevents the induction by aliphatic alcohols of SpoO phenocopies in wild type B. subtilis cells.

Proposed Mechanism for H(II) Phase Induction by Gramicidin in Model Membranes and Its Relation to Channel Formation

A model is proposed for the molecular mechanism of H(II) phase induction by gramicidin in model membranes. The model describes the sequence of events that occurs upon hydration of a mixed lipid/gramicidin film, relating them to gramicidin channel formation and to relevant literature on gramicidin and lipid structure.

Analysis of cryIAa expression in sigE and sigK mutants of Bacillus thuringiensis

The sigE and sigK genes, encoding the sporulation-specific sigma factors sigma 35 and sigma 28 of Bacillus thuringiensis, were each disrupted by inserting a gene conferring resistance to kanamycin into their coding sequences. The B. thuringiensis SigE- and sigK- mutant strains were blocked at different sporulation stages and were unable to sporulate. The SigE-strain was blocked at stage II of sporulation, whereas the SigK- strain was blocked at stage IV. The expression of a cryIAa'-'lacZ transcriptional fusion was analysed in these genetic backgrounds and it was found that both sigma factors are involved in the in vivo transcription of this gene. However, the SigK- strain harbouring the cryIAa gene produced amounts of toxin similar to those produced by the B. thuringiensis Spo+ strain. The toxins accumulated in the mother cell compartment to form a crystal inclusion which remained encapsulated within the cell wall. Thus, transcription from the sigma E-dependent promoter alone (Bt I promoter) is sufficient to support high levels of toxin production in B. thuringiensis.

Sporicidal activity of local anaesthetics and their binary combinations with preservatives

The sporicidal activity of a 1% solution of five local anaesthetics and five preservatives (cetrimide, chlorocresol, chlorhexidine, phenoxyethanol and phenylmercuric nitrate) at their commonly used concentrations, alone and in binary combinations, was determined against Bacillus subtilis and Aspergillus niger spores at different temperature levels by surface viable count technique. The sporicidal activity of all tested systems was temperature dependent and A. niger spores were much more sensitive to the effect of the test systems than B. subtilis spores. The temperatures at which 99% kill is achieved after 30 min exposure were calculated. For local anaesthetics used singly against A. niger the recorded temperatures were 30 degrees C for amethocaine, 45 degrees C for amylocaine, 43 degrees C for cincochaine, 48 degrees C and 50 degrees C for lignocaine and procaine, respectively. A control temperature of 58 degrees C for saline solution was observed. Much higher temperatures were recorded for B. subtilis spores. Cincochaine was the most effective local anaesthetic with a recorded temperature of 60 degrees C for a 99% kill while amylocaine and amethocaine showed temperatures of 84 and 90 degrees C respectively. Procaine, lignocaine as well as the control saline solution recorded temperatures higher than 100 degrees C. Among the 25 binary combinations of local anaesthetics and preservatives tested, the most pronounced potentiation of the sporicidal activity against fungal spores was recorded with chlorocresol combinations, while other combinations of the four remaining preservatives showed different types of interactions at various temperature levels.

Phase separation and hexagonal HII phase formation by gramicidins A, B and C in dioleoylphosphatidylcholine model membranes. A study on the role of the tryptophan residues

The role of the tryptophan-residues in gramicidin-induced HII phase formation was investigated in dioleoylphosphatidylcholine (DOPC) model membranes. 31P-NMR and small angle X-ray diffraction measurements showed, that gramicidin A and C (in which tryptophan-11 is replaced by tyrosine) induce a similar extent of HII phase formation, whereas for gramicidin B and synthetic analogs in which one tryptophan, either at position 9 or 11 is replaced by phenylalanine, a dramatic decrease of the HII phase inducing activity can be observed. Modification of all four tryptophans by means of formylation of the indole NH group leads to a complete block of HII phase formation. Sucrose density centrifugation experiments on the various peptide/lipid samples showed a quantitative incorporation of the peptide into the lipid. For all samples in a 1/10 molar ratio of peptide to lipid distinct bands were found, indicative of a phase separation. For the gramicidin A'/DOPC mixture these bands were analyzed and the macroscopic organization was determined by 31P-NMR and small-angle X-ray diffraction. The results demonstrate that a quantitative phase separation had occurred between a lamellar phase with a gramicidin/lipid ratio of 1/15 and a hexagonal HII phase, which is highly enriched in gramicidin. A study on the hydration properties of tryptophan-N-formylated gramicidin in mixtures with DOPC showed that this analog has a similar dehydrating effect on the lipid headgroup as the unmodified gramicidin. In addition both the hydration study and sucrose density centrifugation experiments showed that, like gramicidin also its analogs have a tendency to aggregate, but with differences in aggregation behaviour which seemed related to their HII phase inducing activity. It is proposed that the main driving force for HII phase formation is the tendency of gramicidin molecules to self-associate and organize into tubular structures such as found in the HII phase and that whether gramicidin (analogs) form these or other types of aggregates depends on their tertiary structure, which is determined by intra- as well as intermolecular aromatic-aromatic stacking interactions.

Sporicidal activity of local anaesthetics and their binary combinations with preservatives

The sporicidal activity of 1% solutions of five local anaesthetics and five preservatives (cetrimide, chlorocresol, chlorhexidine, phenoxyethanol and phenylmercuric nitrate) at their pharmacopeial concentrations, alone and in binary combinations was determined against Bacillus subtilis and Aspergillus niger spores at different temperature levels by the surface viable count technique. The sporicidal activity of all tested systems were temperature dependent. A. niger spores were much more sensitive to the tested systems than B. subtilis spores. The temperature at which 99% of all spores were killed after 30 min exposure time of the anaesthetics were calculated. In case of the local anaesthetics alone against spores of A. niger the recorded temperatures were 30 degrees C for amethocaine, 45 degrees C for both amylocaine and cincochaine, 48 degrees C and 50 degrees C for lignocaine and procaine, respectively, in contrast to 58 degrees C in a control with saline solution. Much higher temperatures were calculated against B. subtilis spores. Cincochaine was the most effective local anaesthetic with a recorded temperature of 60 degrees C, where 99% killing occurred. Amylocaine and amethocaine showed temperatures of 84 degrees C and 90 degrees C, respectively. Procaine, lignocaine as well saline solution as a control caused a 99% killing effect at temperatures higher than 100 degrees C. Among the 25 tested binary combinations of local anaesthetics and preservatives, the highest incidence of potentiation of the sporicidal activity was recorded with chlorocresol combinations, while other combinations of the four remaining preservatives showed different types of interactions at different percentages.

Respiratory systems of the Bacillus cereus mother cell and forespore

The respiratory systems of the mother cells and forespores of Bacillus cereus were compared throughout the maturation stages (III to VI) of sporulation. The results indicated that both cell compartments contain the same assortment of oxidoreductases and cytochromes. However membrane fractions from young forespores were clearly distinct from those of the mother cell, i.e., lower content of cytochrome aa3, lower cytochrome c oxidase activity, higher concentration of cytochrome o, and a lower sensitivity of the respiration to the inhibiting effect of cyanide. This suggests that the cyanide-resistant pathway contributes more importantly to forespore respiratory activity than to activity in the mother cell compartment. During the maturation stages, the forespore NADH oxidase activity declined faster than in the mother cells. Other activities studied decreased steadily in both cell compartments. These findings together with the analysis of the kinetics of NADH-dependent reduction of cytochromes in the mature spore membranes indicated an impairment of electron flow between NADH dehydrogenase and cytochrome b. This impairment could be overcome by the addition of menadione.

Correlation of penicillin-binding protein composition with different functions of two membranes in Bacillus subtilis forespores

The distribution of penicillin-binding proteins (PBPs) within different membranes of sporulating cells of Bacillus subtilis was examined in an effort to correlate the location of individual PBPs with their proposed involvement in either cortical or vegetative peptidoglycan synthesis. The PBP composition of forespores was determined by two methods: examination of isolated forespore membranes and assay of the in vivo accessibility of the PBPs to penicillin. In both cases, it was apparent that PBP 5*, the major PBP synthesized during sporulation, was present primarily, but not exclusively, in the forespore. The membranes from mature dormant spores were prepared by either chemically stripping the integument layers of the spores, followed by lysozyme digestion, or lysozyme digestion alone of coat-defective gerE spores. PBP 5* was detected in membranes from unstripped spores but was never found in stripped ones, which suggests that the primary location of this PBP is the outer forespore membrane. This is consistent with a role for PBP 5* exclusively in cortex synthesis. In contrast, vegetative PBPs 1 and 2A were only observed in stripped spore preparations that were greatly enriched for the inner forespore membrane, which supports the proposed requirement for these PBPs early in germination. The apparent presence of PBP 3 in both membranes of the spore reinforces the suggestion that it catalyzes a step common to both cortical and vegetative peptidoglycan synthesis.

Increased formation of arginine deiminase by Clostridium perfringens FD-1 growing in the presence of caffeine

Caffeine slowed growth and markedly increased the formation of arginine deiminase in growing C. perfringens FD-1 when dextrin, but not maltose or maltotriose, served as the energy source. It is postulated that the ability of caffeine to induce arginine deiminase is related to an inhibition of polysaccharide utilization, resulting in a shift-down condition known to induce arginine deiminase and other enzymes in bacteria.

Induction at high frequency of a unique phenotypic class of Bacillus subtilis mutants by methylxanthines

Caffeine and theophylline are mutagenic at high concentration in the B. subtilis multigene sporulation test for mutagens; caffeine is a stronger mutagen than theophylline in this test. An unusually high fraction of the mutant colonies appear to be phenotypically identical, as judged by colonial morphology and microscopic appearance of the vegetative cells. These mutants do not bring about the pH increase normally associated with sporulation of B. subtilis; such behavior is frequently associated with lack of a functional tricarboxylic acid (TCA) cycle, essential for normal sporulation of this species. Similar mutants have not been noted in the course of screening a variety of well-known mutagens, including acriflavine. Caffeine is maximally effective in inducing these mutants about 10 min after germination commences. Adenosine greatly reduces the ability of caffeine to induce these mutants.

Changes in penicillin-binding proteins during sporulation of Bacillus subtilis

The penicillin-binding proteins (PBPs) of Bacillus subtilis were examined in samples collected at various times from sporulating cultures and compared with the PBPs in a presporulation sample. Large increases in vegetative PBPs 2B and 3 and the appearance of at least one new PBP (42,000 daltons) occurred at reproducible times during sporulation. In some strains a second new PBP (60,000 daltons) was also produced. By comparing the PBP activities in sporulating cells and two spo0 mutants we have classified these changes as sporulation-related events rather than the consequences of stationary-phase aging. The other vegetative PBPs (PBPs 1, 2A, 4, and 5) decreased during sporulation, but not in sufficient amount or at the appropriate time to account for the appearance of the new proteins. A possible connection between specific PBP changes and the penicillin-sensitive stages of sporulation is suggested.

Stimulation of sporulation of Clostridium perfringens by papaverine

Papaverine induced sporulation in Clostridium perfringens, strains FD-1 and PS52; growth was markedly slowed under these conditions. Papaverine induced sporulation in the presence of glucose, a sporulation repressor, although increasing glucose concentrations overcame the papaverine effect. Papaverine induced sporulation of strain FD-1 more effectively than did theophylline.