Effects of Desiccation and Freezing on Microbial Ionizing Radiation Survivability: Considerations for Mars Sample Return

Increasingly, national space agencies are expanding their goals to include Mars exploration with sample return. To better protect Earth and its biosphere from potential extraterrestrial sources of contamination, as set forth in the Outer Space Treaty of 1967, international efforts to develop planetary protection measures strive to understand the danger of cross-contamination processes in Mars sample return missions. We aim to better understand the impact of the martian surface on microbial dormancy and survivability. Radiation resistance of microbes is a key parameter in considering survivability of microbes over geologic times on the frigid, arid surface of Mars that is bombarded by solar and galactic cosmic radiation. We tested the influence of desiccation and freezing on the ionizing radiation survival of six model microorganisms: vegetative cells of two bacteria (Deinococcus radiodurans, Escherichia coli) and a strain of budding yeast (Saccharomyces cerevisiae); and vegetative cells and endospores of three Bacillus bacteria (B. subtilis, B. megaterium, B. thuringiensis). Desiccation and freezing greatly increased radiation survival of vegetative polyploid microorganisms when applied separately, and when combined, desiccation and freezing increased radiation survival even more so. Thus, the radiation survival threshold of polyploid D. radiodurans cells can be extended from the already high value of 25 kGy in liquid culture to an astonishing 140 kGy when the cells are both desiccated and frozen. However, such synergistic radioprotective effects of desiccation and freezing were not observed in monogenomic or digenomic Bacillus cells and endospores, which are generally sterilized by 12 kGy. This difference is associated with a critical requirement for survivability under radiation, that is, repair of genome damage caused by radiation. Deinococcus radiodurans and S. cerevisiae accumulate similarly high levels of the Mn antioxidants that are required for extreme radiation resistance, as do endospores, though they greatly exceed spores in radioresistance because they contain multiple identical genome copies, which in D. radiodurans are joined by persistent Holliday junctions. We estimate ionizing radiation survival limits of polyploid DNA-based life-forms to be hundreds of millions of years of background radiation while buried in the martian subsurface. Our findings imply that forward contamination of Mars will essentially be permanent, and backward contamination is a possibility if life ever existed on Mars.

Comparative accounts of probiotic properties of spore and vegetative cells of Bacillus clausii UBBC07 and in silico analysis of probiotic function

In this study, the spores and vegetative cells of B. clausii were independently evaluated for probiotic properties such as acid, gastric juice, bile, and intestinal fluid tolerance, adhesion to solvents/mucin and zeta potential. In addition, in silico identification of genome features contributing to probiotic properties were investigated. The results showed that spores were highly stable at gastric acidity and capable to germinate and multiply under intestinal conditions as compared to vegetative cells. The higher hydrophobicity of spores, compared to vegetative cells, is advantageous for colonization and persistence in the intestine. Furthermore, the presence of F ₀ F ₁ ATP synthase, amino acid decarboxylase, bile acid symporter, mucin/collagen/fibronectin-binding proteins, heat/cold shock proteins, and universal stress proteins suggests that the strain is able to survive stress. In conclusion, the results demonstrate that B. clausii UBBC07 spores show significantly higher survival and adhesion in in vitro gastrointestinal conditions as compared to vegetative cells. Besides, this study provides a comparative analysis of the in vitro probiotic properties of spores and vegetative cells of Bacillus clausii UBBC07.

Thermal Reduction of Bacillus spp. in Naturally Contaminated Mesquite Flour with Two Different Water Activities

ABSTRACT

Mesquite flour with endogenous high sugar content is often contaminated with Bacillus cereus. The purpose of the present study was to evaluate the thermal resistance of Bacillus spp. in naturally contaminated mesquite flour. Flours with and without adjusted water activity (aw) were treated at various temperatures (100 to 140°C) and times (up to 2 h). Total mesophilic bacteria and Bacillus spp. were enumerated using tryptic soy agar and Brilliance Bacillus cereus Agar, respectively. Results revealed that naturally contaminated Bacillus spp. and other mesophilic bacteria in mesquite flour (aw = 0.34) were highly resistant to heat. To reduce the initial populations (4.75 log CFU/g) of Bacillus spp. to nondetectable levels (<1.18 log CFU/g), thermal treatments of 120°C for 2 h were required. D100°C-values for total mesophilic bacteria were 5.6-fold higher than those of Bacillus spp. With increasing treatment temperature, the difference in D-value between total mesophilic bacteria and Bacillus spp. became smaller. When the aw of flour was adjusted from 0.34 to 0.71, the D-values for Bacillus decreased significantly. Treatment at 100°C for 1 h reduced Bacillus spp. populations to nondetectable levels. Our results demonstrate that naturally present Bacillus spp. in flour are highly resistant to heat, whereas increasing the aw increased their heat sensitivity. The high thermal resistance of microbes in mesquite flour warrants further investigations.

HIGHLIGHTS

Importance of the gastrointestinal life cycle of Bacillus for probiotic functionality

Bacillus spp. are widely used in animal production for their probiotic properties. In many animal species, feed supplementation with specific Bacillus strains can provide numerous benefits including improvement in digestibility, the gut microbiota and immune modulation, and growth performance. Bacilli are fed to animals as spores that can sustain the harsh feed processing and long storage. However, the spores are metabolically quiescent and it is widely accepted that probiotics should be in a metabolically active state to perform certain probiotic functions like secretion of antimicrobial compounds and enzymes, synthesis of short chain fatty acids, and competition for essential nutrients. These functions should become active in the host gastrointestinal tract (GIT) soon after digestion of spores in order to contribute to microbiota and host metabolism. Considering that bacterial spores are metabolically dormant and many health benefits are provided by vegetative cells, it is of particular interest to discuss the life cycle of Bacillus in animal GIT. This review aims to capture the main characteristics of spores and vegetative cells and to discuss the latest knowledge in the life cycle of beneficial Bacillus in various intestinal environments. Furthermore, we review how the life cycle may influence probiotic functions of Bacillus and their benefits for human and animal health.

Synchronization of Bacillus subtilis Cells by Spore Germination and Outgrowth

This protocol defines conditions under which the germination of spores can be used to synchronize Bacillus subtilis cells, utilizing the time-ordered sequence of events taking place during the transition from spore to vegetative cells. The transition stages involve: phase change, swelling, emergence, initial division, and elongation. By using this method we have obtained two distinctive synchronized cell cycles, while the synchrony faded away in the third cycle. The advantage of using spore outgrowth and germination is that a highly synchronized population of bacterial cells can be obtained. Non-dividing spores stay synchronized, while synchrony rapidly decays during a few divisions. The limitations of this method are that it can be applied only for sporulating bacteria and synchrony lasts for only a limited period of time exceeding not more than two cycles.

A pilot study to assess bacterial and toxin reduction in patients with Clostridium difficile infection given fidaxomicin or vancomycin

BACKGROUND

To assess the effect of fidaxomicin and vancomycin on Clostridium difficile toxins and correlation with clinical and microbiologic outcomes.

METHODS

Hospitalized patients with C. difficile infection were randomly assigned a 10-day course of fidaxomicin or vancomycin. Stool samples collected at baseline (day 0), mid-therapy (days 3-5), end of therapy (days 10-13) and follow-up (days 19-38) were assessed for quantity of toxins A and B as well as spore and vegetative cells counts. Correlation of toxins concentrations with microbiologic and clinical findings were evaluated.

RESULTS

Among 34 patients 12 had detectable toxin concentrations at baseline seven were randomized to fidaxomicin and five to vancomycin. Overall both fidaxomicin and vancomycin resulted in drop of both toxins concentrations by midpoint of therapy. The drop in toxin A concentrations was maintained up to the follow-up period with fidaxomicin but not with vancomycin even in patients who developed recurrence. Patients who developed recurrence in the fidaxomicin group had lower concentrations of toxin B versus the recurrence patient of vancomycin group. Presence of vegetative cells and spores was significantly linked with high toxin A (P = 0.003 and <0.001 respectively) and toxin B (P = 0.007 and <0.001 respectively) concentrations across time points. Toxin B concentrations but not A significantly correlated with stool consistency (P < 0.001) and frequency (P = 0.05).

CONCLUSIONS

Fidaxomicin was associated with sustained reduction of both toxins up to 30 days post therapy versus vancomycin. Multiple clinical or microbiologic observations were correlated with toxin A or B concentrations.

Reverse transcription polymerase chain reaction-based method for selectively detecting vegetative cells of toxigenic Clostridium difficile

The laboratory diagnostic methods for Clostridium difficile infection (CDI) include toxigenic culture, enzyme immunoassays (EIAs) to detect the toxins of C. difficile, and nucleic acid amplification tests (NAATs) to detect C. difficile toxin genes, but each of these methods has disadvantages; toxigenic cultures require a long time to produce results, EIAs have low sensitivity, and NAATs that target DNA cannot distinguish vegetative cells from spores and dead cells. Here we report a new detection method that uses reverse transcription polymerase chain reaction to target the toxin-gene transcripts. This method was able to specifically detect the vegetative cells of toxigenic C. difficile in fecal samples in spike tests, with a minimum detection limit of 5 × 10(2) colony-forming units per 100 mg of stool specimen. The performance of this method was also demonstrated in a pilot scale evaluation using clinical fecal specimens, which showed that this method may be more sensitive than EIA and requires a shorter time than toxigenic culture. This method could potentially be applied in the clinical laboratory to detect C. difficile in fecal specimens. The ability of this method to discriminate the presence of vegetative cells from spores and dead cells could help to further the understanding of CDI.

nov (Group IV): Resting cyst distribution and toxin profile of vegetative cells in Bizerte Lagoon (Tunisia, Southern Mediterranean Sea)

A high spatial resolution sampling of Alexandrium pacificum cysts, along with sediment characteristics (% H₂O, % organic matter (OM), granulometry), vegetative cell abundance and environmental factors were investigated at 123 study stations in Bizerte Lagoon (Tunisia). Morphological examination and ribotyping of cells obtained from a culture called ABZ1 obtained from a cyst isolated in lagoon sediment confirmed that the species was A. pacificum. The toxin profile from the ABZ1 culture harvested during exponential growth phase was simple and composed of the N-sulfocarbamoyl toxins C1 (9.82pgtoxincell^-1), the GTX6 (3.26pgtoxincell^-1) and the carbamoyl toxin Neo-STX (0.38pgtoxincell^-1). The latter represented only 2.8% of the total toxins in this strain. High abundance of A. pacificum cysts correlated with enhanced percentages of water and organic matter in the sediment. In addition, sediment fractions of less than 63μm were examined as a favorable potential seedbed for initiation of future blooms and outbreaks of A. pacificum in the lagoon. A significant difference in the cyst distribution pattern was recorded among the lagoon's different zones, with the higher cyst abundance occurring in the inner waters. Also, no correlation due to the specific hydrodynamics of the lagoon was observed in the spatial distribution of A. pacificum cysts and vegetative cells.

Toxin producing Bacillus cereus persist in ready-to-reheat spaghetti Bolognese mainly in vegetative state

The potential of Bacillus cereus to cause a diarrheal toxico-infection is related to its ability to perform de novo enterotoxin production in the small intestine. A prerequisite for this is presence of sufficient numbers of B. cereus that have survived gastro-intestinal passage. It is known that the percentage of survival is much smaller for vegetative cells in comparison to spores and it is therefore important to know the state in which B. cereus is ingested. The results of the current study performed on twelve B. cereus strains, comprising both diarrheal and emetic type, indicate that exposure via contaminated foods mainly concerns vegetative cells. Inoculated vegetative cells grew to high counts, with the growth dynamic depending on the storage temperature. At 28 °C growth to high counts resulted in spore formation, in general, after 1 day of storage. One strain was an exception, producing spores only after 16 days. At 12 °C obtained high counts did not result in spore formation for 11 of 12 tested strains after two weeks of storage. The highest counts and time to sporulation were different between strains, but no difference was observed on the group level of diarrheal and emetic strains. The spore counts were always lower than vegetative cell counts and occurred only when food was obviously sensory spoiled (visual and odor evaluation). Similar observations were made with food inoculated with B. cereus spores instead of vegetative cells. Although the prospect of consuming spores was found very weak, the numbers of vegetative B. cereus cells were high enough, without obvious sensory deviation, to survive in sufficient level to cause diarrheal toxico-infection.

Behavioural pattern of vegetative cells and spores of Bacillus cereus as affected by time-temperature combinations used in processing of Indian traditional foods

This study was undertaken to evaluate the behaviour of vegetative cells and spores of four potent native toxigenic food isolates of Bacillus cereus as affected by selected time-temperature combinations used in processing of Indian traditional foods. The vegetative cells of B. cereus when subjected to sublethal heat treatments, individually, in different heating menstra showed a sigmoidal inactivation pattern, with D-values in the range of 3.45 min at 60 °C to 10.6 min at 56 °C in saline. Accordingly, the z-values recorded across the heating menstra ranged from 9.3 °C in culture broth to 24 °C in whole milk. Similarly, the inactivation pattern for spores for the same isolates was curvilinear with D-values ranging from 4.4 min at 95 °C in whole milk to 19.45 min at 85 °C in saline. The z-values for spores ranged from 16.6 °C in saline to 38.4 °C in whole milk. The thermal inactivation pattern observed for vegetative cells and spores indicate that the death rate was not constant during the process of heat treatment.