A rapid staining technique for the detection of the initiation of germination of bacterial spores

Molecular Characterization Reveals Biodiversity and Biopotential of Rhizobacterial Isolates of Bacillus Spp

Bacillus species appearas the most attractive plant growth-promoting rhizobacteria (PGPR) and alternative to synthetic chemical pesticides. The present study examined the antagonistic potential of spore forming-Bacilli isolated from organic farm soil samples of Allahabad, India. Eighty-seven Bacillus strains were isolated and characterized based on their morphological, plant growth promoting traits and molecular characteristics. The diversity analysis used 16S-rDNA, BOX-element, and enterobacterial repetitive intergenic consensus. Two strains, PR30 and PR32, later identified as Bacillus sp., exhibited potent in vitro antagonistic activity against Ralstonia solanaceorum. These isolates produced copious amounts of multiple PGP traits, such as indole-3-acetic acid (40.0 and 54.5 μg/mL), phosphate solubilization index (PSI) (4.4 and 5.3), ammonia, siderophore (3 and 4 cm), and 1-aminocyclopropane-1-carboxylate deaminase (8.1and 9.2 μM/mg//h) and hydrogen cyanide. These isolates were subjected to the antibiotic sensitivity test. The two potent isolates based on the higher antagonistic and the best plant growth-promoting ability were selected for plant growth-promoting response studies in tomatoe, broccoli, and chickpea. In the pot study, Bacillus subtilis (PR30 and PR31) showed significant improvement in seed germination (27-34%), root length (20-50%), shoot length (20-40%), vigor index (50-75%), carotenoid content (0.543-1.733), and lycopene content (2.333-2.646 mg/100 g) in tomato, broccoli, and chickpea. The present study demonstrated the production of multiple plant growth-promoting traits by the isolates and their potential as effective bioinoculants for plant growth promotion and biocontrol of phytopathogens.

Microscopy methods for Clostridioides difficile

Microscopic technologies including light and fluorescent, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and cryo-electron microscopy have been widely utilized to visualize Clostridioides difficile at the molecular, cellular, community, and structural biology level. This comprehensive review summarizes the microscopy tools (fluorescent and reporter system) in their use to study different aspects of C. difficile life cycle and virulence (sporulation, germination) or applications (detection of C. difficile or use of antimicrobials). With these developing techniques, microscopy tools will be able to find broader applications and address more challenging questions to study C. difficile and C. difficile infection.

Tumebacillus lacus sp. nov., isolated from lake water

A Gram-stain-positive, aerobic, rod-shaped, endospore-forming and motile, by means of peritrichous flagella, bacterium, designated DT12T, was isolated from a lake water sample from Datun Lake of Yunnan Province, PR China. The results of phylogenetic analysis based on 16S rRNA gene sequence and the concatenated alignment of 120 ubiquitous single-copy proteins indicated that the novel strain represented a member of the genus Tumebacillus. The sole quinone was menaquinone-7 and the cell-wall peptidoglycan was type-A1γ. The major fatty acids (>10 %) of the novel strain were iso-C15 : 0 and anteiso-C15 : 0, while the major polar lipids were phosphatidylmonomethylethanolamine, phosphatidylethanolamine and phosphatidylglycerol. The results of phylogenetic analyses combined with phylogenetic, phenotypic and chemotaxonomic features, strongly supported the hypothesis that the strain should be classified as representing a novel species of the genus Tumebacillus, for which the name Tumebacillus lacus sp. nov. is proposed. The type strain is DT12T (=KCTC 33958T= MCCC 1H00320T). The genomic analysis revealed that DT12T has various biosynthetic gene clusters for secondary metabolites, and members of the genus Tumebacillus may represent a promising source of new natural products. Our study also showed that members of the genus Tumebacillus are widely distributed in a variety of habitats throughout the globe, particularly in soils, human-, animal- and plant-associated environments. Members of the genus Tumebacillus may have an important role in the growth and health of humans, plants and animals.

Comparison of sporulation and germination conditions for Clostridium perfringens type A and G strains

Clostridium perfringens is a spore forming, anaerobic, Gram-positive bacterium that causes a range of diseases in humans and animals. C. perfringens forms spores, structures that are derived from the vegetative cell under conditions of nutrient deprivation and that allows survival under harsh environmental conditions. To return to vegetative growth, C. perfringens spores must germinate when conditions are favorable. Previous work in analyzing C. perfringens spore germination has produced strain-specific results. Hence, we analyzed the requirements for spore formation and germination in seven different C. perfringens strains. Our data showed that C. perfringens sporulation conditions are strain-specific, but germination responses are homogenous in all strains tested. C. perfringens spores can germinate using two distinct pathways. The first germination pathway (the amino acid-only pathway or AA) requires L-alanine, L-phenylalanine, and sodium ions (Na⁺) as co-germinants. L-arginine is not a required germinant but potentiates germination. The AA pathway is inhibited by aromatic amino acids and potassium ions (K⁺). Bicarbonate (HCO₃^-), on the other hand, bypasses potassium-mediated inhibition of C. perfringens spore germination through the AA pathway. The second germination pathway (the bile salt / amino acid pathway or BA) is more promiscuous and is activated by several bile salts and amino acids. In contrast to the AA pathway, the BA pathway is insensitive to Na⁺, although it can be activated by either K⁺ or HCO₃^-. We hypothesize that some C. perfringens strains may have evolved these two distinct germination pathways to ensure spore response to different host environments.

Vallitalea longa sp. nov., an anaerobic bacterium isolated from marine sediment

A novel bacterium, strain SH18-1^T, was isolated from marine sediment collected near Sado Island in the Sea of Japan. This strain was strictly anaerobic, Gram-stain-negative, non-spore-forming, rod-shaped, motile, and mesophilic. It grew at 15-40 °C (optimum, 30-35 °C), at a NaCl concentration of 0.2-5.0 % (w/v; optimum, 1.5-2.5 %), and at pH 5.5-8.5 (optimum, pH 7.0). Results of 16S rRNA gene phylogenetic analysis showed a similarity value of 97.49 % between strain SH18-1^T and Vallitalea guaymasensis Ra1766G1^T, which was the most closely related species. The genome size of strain SH18-1^T was 5.71 Mb and its G+C content was 30.2 mol%. Genome sequence analyses for comparison between strain SH18-1^T and V. guaymasensis Ra1766G1^T showed values lower than the threshold for species demarcation determined using the Genome-to-Genome Distance Calculator and the Average Nucleotide Identity Calculator. Elemental sulphur, sulphate, thiosulphate, sulphite, fumarate, nitrate, and nitrite were not used as terminal electron acceptors. The major fatty acids in strain SH18-1^T were iso-C_15 : 0, anteiso-C_15 : 0, and C_16 : 0, and the detected polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphoglycolipid, glycolipid, three unidentified phospholipids, and one unidentified polar lipid. From these results, strain SH18-1^T (=NBRC 115488^T=DSM 114058^T) is suggested to represent a novel species of the genus Vallitalea and the name Vallitalea longa sp. nov. is proposed.

Potential control of the infective stage of Taenia pisiformis using Bacillus thuringiensis GP526 strain

The GP526 strain of Bacillus thuringiensis has been referred as an in vitro helminthicide on various stages of Dipylidium caninum and Centrocestus formosanus. Our study addresses the in vitro ovicidal activity of GP526 strain spore-crystal complex on Taenia pisiformis eggs, evaluating induced damage microscopically. The eggs exposed to the total extract containing spores and crystals show damage after 24 hours, with loss of integrity on the eggshell, and an ovicidal activity of 33% at 1mg/ml. The destruction of the embryophore was observed after 120 h with a 72% of ovicidal activity at 1 mg/ml. The LC50 was 609.6 μg/ml, dose that causes a 50% of lethality on the hexacanth embryo, altering the oncosphere membrane. The spore-crystal proteins were extracted, and the protein profile was obtained by electrophoresis, finding a major band of 100 kDa suggestive of an S-layer protein, since an S-layer was immunodetected in both, spores and extracted proteins. The protein fraction containing the S-layer protein presents adhesion to the T. pisiformis eggs, and 0.4 mg/ml of the protein induces a lethality of 21.08% at 24 h. The characterization of molecular mechanisms of ovicidal activity will be an important contribution, so the characterization of the proteins that make up the extract of the GP526 strain, would be useful to support the biological potential for control of this cestodiasis and other parasitosis. B. thuringiensis is shown as a potent helminthicide on eggs, with useful potential for biological control of this cestodiasis.

Mechanism insights into bacterial sporulation at natural sphalerite interface with and without light irradiation: The suppressing role in bacterial sporulation by photocatalysis

Unveiling the mechanisms of bacterial sporulation at natural mineral interfaces is crucial to fully understand the interactions of mineral with microorganism in aquatic environment. In this study, the bacterial sporulation mechanisms of Bacillus subtilis (B. subtilis) at natural sphalerite (NS) interface with and without light irradiation were systematically investigated for the first time. Under dark condition, NS was found to inactivate vegetative cells of B. subtilis and promote their sporulation simultaneously. The released Zn2+ from NS was mainly responsible for the bacterial inactivation and sporulation. With light irradiation, the photocatalytic effect from NS could increase the bacterial inactivation efficiency, while the bacterial sporulation efficiency was decreased from 8.1 % to 4.5 %. The photo-generated H2O2 and O2- played the major roles in enhancing bacterial inactivation and suppressing bacterial sporulation process. The intracellular synthesis of dipicolinic acid (DPA) as biomarker for sporulation was promoted by NS in dark, which was suppressed by the photocatalytic effect of NS with light irradiation. The transformation process from vegetative cells to spores was monitored by both 3D-fluerecence EEM and SEM observations. Compared with the NS alone system, the NS/light combined system induced higher level of intracellular ROSs, up-regulated antioxidant enzyme activity and decreased cell metabolism activity, which eventually led to enhanced inactivation of vegetative cells and suppressed bacterial sporulation. These results not only provide in-depth understanding about bacterial sporulation as a new mode of sub-lethal stress response at NS interface, but also shed lights on putting forward suitable strategies for controlling spore-producing bacteria by suppressing their sporulation during water disinfection.

Susceptibility of Vegetative Cells and Endospores of Bacillus cereus to Rhamnolipid Biosurfactants and Their Potential Application in Dairy

Bacillus cereus is a Gram-positive, endospore-forming bacterium well-known as a food pathogen that causes great losses in the food industry, especially in dairy. In this study, rhamnolipid (RL) biosurfactants were evaluated as a bio-based alternative for controlling the growth of vegetative cells and endospores of B. cereus. RLs were tested against 14 B. cereus strains isolated from different types of foodstuffs. The antimicrobial activity against vegetative cells and endospores revealed minimal inhibitory concentration (MIC) values of 0.098 mg/mL for almost all strains tested and minimal bactericidal concentration (MBC) varying between 0.098 and >25 mg/mL. The presence of RLs inhibited endospore germination by more than 99%, reducing by 5.5 log the outgrowth of strain 0426. Scanning and transmission electron microscopy confirmed that exposure to RL causes damage to the structure of endospores. When skim milk was utilized as a food model, RL inhibited the growth of vegetative cells and endospores of B. cereus, showing MBC of 3.13 mg/mL for the vegetative cells of strain 0426. The surfactant also reduced bacterial growth in milk at refrigerator temperature. The results suggest that RLs are promising candidates for the development of novel strategies to control B. cereus in the food industry.

Facilitated endospore detection for Bacillus spp. through automated algorithm‐based image processing

Bacillus spp. endospores are important dormant cell forms and are distributed widely in environmental samples. While these endospores can have important industrial value (e.g. use in animal feed as probiotics), they can also be pathogenic for humans and animals, emphasizing the need for effective endospore detection. Standard spore detection by colony forming units (CFU) is time‐consuming, elaborate and prone to error. Manual spore detection by spore count in cell counting chambers via phase‐contrast microscopy is less time‐consuming. However, it requires a trained person to conduct. Thus, the development of a facilitated spore detection tool is necessary. This work presents two alternative quantification methods: first, a colorimetric assay for detecting the biomarker dipicolinic acid (DPA) adapted to modern needs and applied for Bacillus spp. and second, a model‐based automated spore detection algorithm for spore count in phase‐contrast microscopic pictures. This automated spore count tool advances manual spore detection in cell counting chambers, and does not require human overview after sample preparation. In conclusion, this developed model detected various Bacillus spp. endospores with a correctness of 85–89%, and allows an automation and time‐saving of Bacillus endospore detection. In the laboratory routine, endospore detection and counting was achieved within 5–10 min, compared to up to 48 h with conventional methods. The DPA‐assay on the other hand enabled very accurate spore detection by simple colorimetric measurement and can thus be applied as a reference method.

New ribotype Clostridioides difficile from ST11 group revealed higher pathogenic ability than RT078

Clostridioides difficile is the predominant antibiotic-associated enteropathogen associated with diarrhoea or pseudomembranous colitis in patients worldwide. Previously, we identified C. difficile RT078 isolates (CD21062) from elderly patients in China, including two new ribotype strains (CD10010 and CD12038) belonging to the ST11 group, and their genomic features were also investigated. This study compared sporulation, spore germination, toxin expression, flagellar characteristics, and adhesion among these strains in vitro and analysed their pathogenic ability in vivo using animal models. The results showed sporulation and spore germination did not significantly differ among the three C. difficile strains. CD10010 and CD12038 showed higher transcriptional levels of toxins until 48 h; thereafter, the transcriptional levels of toxins remained constant among RT078, CD10010, and CD12038. RT078 showed a loss of flagellum and its related genes, whereas CD12038 showed the highest motility in vitro. Both CD10010 and CD12038 initially showed flg phase OFF, and the flagellar switch reversed to phase ON after 48 h in swim agar. Flagellar proteins and toxins were both upregulated when flg phase OFF changed to flg phase ON status, enhancing their pathogenic ability. CD12038 showed the highest adhesion to Hep-2 cells. Histopathology and inflammation scores demonstrated that CD12038 caused the most severe tissue damage and infection in vivo. The new ribotype strains, particularly CD12038, exhibit higher pathogenic ability than the typical RT078 strain, both in vitro and in vivo. Therefore, more attention should be paid to this new C. difficile strain in epidemiological research; further studies are warranted.

Histological Stains in the Past, Present, and Future

Certain contemporary histology stains and methods are not the same as those used in the past. This progression has delved into the requirement for more precise, less complex, and efficient staining procedures. The objective of this study is to assess historical and contemporary stains and procedures, as well as the challenges surrounding their improvement. Carmine, hematoxylin, silver nitrate, Giemsa, trichome stain, Gram stain, and mauveine were among the first histological stains discovered in nature. Aside from their utility in the study of tissues at the time, they also laid the groundwork for the development of commercial dyes that are still in use today. Hematoxylin and eosin, Ziehl-Nielsen (ZN) stain, periodic acid-Schiff stain, and Grocott-Gomori methenamine silver stain are some of the most recently developed histological stains. The future of histological stains and processes appears to be influenced by technological advancements and the demand for cost-effective diagnostic approaches in the healthcare system. Thus, currently used histological stains appear to be economical, quick, and reliable tools for interpreting, archiving, and delivering essential diagnoses that could not be achieved by any other means.

Teicoplanin Suppresses Vegetative Clostridioides difficile and Spore Outgrowth

In recent decades, the incidence of Clostridioides difficile infection (CDI) has remained high in both community and health-care settings. With the increasing rate of treatment failures and its ability to form spores, an alternative treatment for CDI has become a global priority. We used the microdilution assay to determine minimal inhibitory concentrations (MICs) of vancomycin and teicoplanin against 30 distinct C. difficile strains isolated from various host origins. We also examined the effect of drugs on spore germination and outgrowth by following the development of OD₆₀₀. Finally, we confirmed the spore germination and cell stages by microscopy. We showed that teicoplanin exhibited lower MICs compared to vancomycin in all tested isolates. MICs of teicoplanin ranged from 0.03-0.25 µg/mL, while vancomycin ranged from 0.5-4 µg/mL. Exposure of C. difficile spores to broth supplemented with various concentrations of antimicrobial agents did not affect the initiation of germination, but the outgrowth to vegetative cells was inhibited by all test compounds. This finding was concordant with aberrant vegetative cells after antibiotic treatment observed by light microscopy. This work highlights the efficiency of teicoplanin for treatment of C. difficile through prevention of vegetative cell outgrowth.

Combining Celery Oleoresin, Limonene and Rhamnolipid as New Strategy to Control Endospore-Forming Bacillus cereus

Foodborne diseases (FBD) are a great problem worldwide, leading millions of people to seek medical help and to significant economic losses for industry. Among the agents implicated in FDB is Bacillus cereus, a Gram-positive, toxigenic and endospore-forming bacterium. In this study, rhamnolipid (RL) biosurfactant, celery oleoresin (OR) and limonene (LN) were evaluated as bio-based alternatives for controlling the growth of vegetative cells and endospores of B. cereus. To address their antimicrobial activity, the compounds were tested separately and in combination. Results demonstrate that, when combined with RL, both OR and LN have lower minimal inhibitory concentration (MIC) values and increased endospore inhibition potential. A percentage of endospore inhibition from 73% to 98%, corresponding to a 2.8-3.6 log reduction in spore outgrowth, was observed. RL inhibited B. cereus growth and endospore germination and potentially enhanced the antimicrobial efficacy of the natural hydrophobic compounds tested.

Description of Cohnella zeiphila sp. nov., a bacterium isolated from maize callus cultures

A Gram-stain positive, aerobic, motile, rod-shaped bacterium designated as strain CBP-2801^T was isolated as a contaminant from a culture containing maize callus in Peoria, Illinois, United States. The strain is unique relative to other Cohnella species due to its slow growth and reduced number of sole carbon sources. Phylogenetic analysis using 16S rRNA indicated that strain CBP-2801^T is a Cohnella bacterium and showed the highest similarity to Cohnella xylanilytica (96.8%). Genome-based phylogeny and genomic comparisons based on average nucleotide identity confirmed the strain to be a novel species of Cohnella. Growth occurs at 15-45 °C (optimum 40 °C), pH 5-7 (optimum pH 6) and with 0-1% NaCl. The predominant fatty acids are anteiso-15:0 and 18:1 ω6c. Genome mining for secondary metabolites identified a putative biosynthetic cluster that encodes for a novel lasso peptide. In addition, this study contributes five new genome assemblies of type strains of Cohnella species, a genus with less than 30% of the type strains sequenced. The DNA G + C content is 58.7 mol %. Based on the phenotypic, phylogenetic and biochemical data strain CBP-2801^T represents a novel species, for which the name Cohnella zeiphila sp. nov. is proposed. The type strain is CBP-2801^T (= DSM 111598 = ATCC TSD-230).

Comparative genomics identifies potential virulence factors in Clostridium tertium and C. paraputrificum

Some well-known Clostridiales species such as Clostridium difficile and C. perfringens are agents of high impact diseases worldwide. Nevertheless, other foreseen Clostridiales species have recently emerged such as Clostridium tertium and C. paraputrificum. Three fecal isolates were identified as Clostridium tertium (Gcol.A2 and Gcol.A43) and C. paraputrificum (Gcol.A11) during public health screening for C. difficile infections in Colombia. C. paraputrificum genomes were highly diverse and contained large numbers of accessory genes. Genetic diversity and accessory gene percentage were lower among the C. tertium genomes than in the C. paraputrificum genomes. C. difficile tcdA and tcdB toxins encoding homologous sequences and other potential virulence factors were also identified. EndoA interferase, a toxic component of the type II toxin-antitoxin system, was found among the C. tertium genomes. toxA was the only toxin encoding gene detected in Gcol.A43, the Colombian isolate with an experimentally-determined high cytotoxic effect. Gcol.A2 and Gcol.A43 had higher sporulation efficiencies than Gcol.A11 (84.5%, 83.8% and 57.0%, respectively), as supported by the greater number of proteins associated with sporulation pathways in the C. tertium genomes compared with the C. paraputrificum genomes (33.3 and 28.4 on average, respectively). This work allowed complete genome description of two clostridiales species revealing high levels of intra-taxa diversity, accessory genomes containing virulence-factors encoding genes (especially in C. paraputrificum), with proteins involved in sporulation processes more highly represented in C. tertium. These finding suggest the need to advance in the study of those species with potential importance at public health level.

Longirhabdus pacifica gen. nov., sp. nov., isolated from a deep-sea hydrothermal sediment in the West Pacific Ocean

A novel Gram-stain-negative bacterium, designated as SCSIO 06110^T, was isolated from a deep-sea sediment of the West Pacific Ocean. Cells were 0.5-0.8 µm in width and 3.0-4.0 µm in length, spore-forming, rod-shaped with peritrichous flagella. Positive for catalase and urease, negative for oxidase and nitrate reduction. Growth occurred at 15-37 °C, pH 6-9 and 1-5 % (w/v) NaCl, with optimum growth at 28 °C, pH 7 and 3 % (w/v) NaCl. MK-7 was the only menaquinone. The strain possessed diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and two unidentified phospholipids. Iso-C_16 : 0, iso-C_15 : 0 and iso-C_14 : 0 were the major fatty acids. The novel isolate clustered with genera in the family Paenibacillaceae, but formed a separated branch with the closest relative Chengkuizengella sediminis J15A17^T (91.1 % sequence similarity) when compared in a phylogenetic analysis of 16S rRNA gene sequences. The DNA G+C content of strain SCSIO 06110^T was 38.5 mol%. Based on the polyphasic data presented, a new genus, Longirhabdus gen. nov., is proposed in the family Paenibacillaceae with the type species Longirhabdus pacifica sp. nov. and the type strain SCSIO 06110^T (=DSM 105158^T=CGMCC 1.16550^T).

The ability of spore formers to degrade milk proteins, fat, phospholipids, common stabilizers, and exopolysaccharides

Spore formers are common spoilage-causing microorganisms in dairy products; however, their modes of spoilage (proteolysis, lipolysis, etc.) have not been described in detail for cultured dairy products such as sour cream and yogurt. The objective of the present study was to test the ability of spore-forming strains isolated from dairy environments for their spoilage-causing activities at typical sour cream (24°C) and yogurt (42°C) fermentation temperatures. A total of 25 spore-forming strains were isolated from different sources, including raw milk, pasteurizer balance tank, biofilms formed on heat exchangers, and milk powder. These strains were tested for proteolytic and lipolytic activities and for their ability to degrade phospholipids, common stabilizers (starch, gelatin, xanthan gum, pectin), and exopolysaccharides (EPS) at sour cream and yogurt fermentation temperatures. A higher percentage of positive strains was observed for selected activities at yogurt fermentation temperature compared with sour cream fermentation temperature. Identified proteolytic spore-forming strains, based on a skim milk agar method, were subsequently quantified for their level of proteolysis using non-casein nitrogen (NCN) content and sodium dodecyl sulfate-PAGE (SDS-PAGE). The proteolytic strains that showed the highest levels of proteolysis (highest percentages of NCN content) at 24°C were Bacillus mojavensis BC, Bacillus cereus DBC, Bacillus subtilis DBC, B. mojavensis DBC1, and Paenibacillus polymyxa DBC1. At 42°C the strains with the highest levels of proteolysis (highest percentages of NCN content) were B. subtilis DBC, B. mojavensis BC, B. mojavensis DBC1, B. cereus DBC, and Bacillus licheniformis DBC6. Results of SDS-PAGE demonstrated that proteolytic strains had primarily hydrolyzed β- and κ-CN. A viscometric method was used to evaluate the susceptibility of exopolysaccharides (EPS) to degradation by selected spore formers. This method helped to determine that EPS produced by commercial yogurt and sour cream cultures is susceptible to degradation by spore formers present in dairy environments.

Uncured-Labeled Meat Products Produced Using Plant-Derived Nitrates and Nitrites: Chemistry, Safety, and Regulatory Considerations

Consumers often malign conventional curing agents while concomitantly accepting the natural forms of the same constituents in numerous food products. This paradox ostensibly exceeds all other food-related controversies to date and likely contributes to the rapid expansion of meat products that utilize natural nitrate derivatives. While there is high demand for these products, a fundamental lack of understanding regarding the safety and chemical implications of curing agents, whether derived from synthetic or natural sources, continues to persist. This manuscript elucidates the variations among curing preparations with particular emphasis pertaining to the associated safety, chemical, and regulatory ramifications encompassing these product categories.

Inactivation of Bacillus subtilis spores at various germination and outgrowth stages using intense pulsed light

It is important to inactivate spore-forming bacteria in foods because their spores are highly resistant to various stresses. Although thermal treatment is an effective inactivation method, the associated high temperatures can cause changes in food quality. Intense pulsed light (IPL) is a nonthermal technique that can effectively improve food safety. This study evaluated the inactivation effects of IPL at various fluences on Bacillus subtilis spores. IPL treatment at a total fluence of 7.40 J/cm² resulted in a 7 log reduction, indicating the potential of IPL to effectively inactivate bacterial spores. The sensitivity of B. subtilis spores to IPL during germination and outgrowth was also measured. The resistance to the IPL increased temporarily until 1 h after the start of incubation, and then gradually decreased for longer incubation periods. This temporary increase in resistance at the early stage of incubation was attributed to the leakage of dipicolinic acid from the spores. The results also showed that the inactivation efficiency increases after 1 h pre-incubation because the numbers of vegetative cells increased with the incubation time.

Non-toxigenic strain of Clostridioides difficile Z31 reduces the occurrence of C. difficile infection (CDI) in one-day-old piglets on a commercial pig farm

Neonatal porcine diarrhea (NPD) is a current problem on pig farms and is caused by several enteropathogens. Among them, Clostridioides difficile stands out due to its importance in piglets and zoonotic potential. A non-toxigenic strain of C. difficile (NTCD), named Z31, was previously tested in hamster and piglet experimental models as a strategy to prevent C. difficile infection (CDI). To evaluate the capacity of the strain Z31 to prevent CDI and NPD in one-day-old piglets on a commercial farm, 90 piglets from 16 litters received 1 × 10⁶ spores of Z31 while 84 animals from the same litters served as controls. Animals were clinically evaluated, and fecal samples were collected 24 h after administration and submitted to A/B toxin detection and isolation of C. difficile. Stool samples were also submitted to rotavirus, Escherichia coli, and Clostridium perfringens detection. Administration of Z31 reduced the incidence of CDI in treated animals (7.8%) when compared to the control group (25.0%; P = 0.003). In animals that developed CDI, the intensity of diarrhea was lower in those that received Z31 than in the control group. Neonatal porcine diarrhea was reduced in treated animals when compared to untreated animals (P < 0.001). The present study suggests that Z31 can potentially be used to prevent CDI in piglets on commercial farms.

Evaluation of growth and sporulation of a non-toxigenic strain of Clostridioides difficile (Z31) and its shelf viability

The oral administration of non-toxigenic strains of Clostridioides difficile (NTCD) is currently showing promising results for the prevention of Clostridioides difficile infection (CDI) in humans and animals, and is being considered as a possible commercial product to be used in the near future. The aim of this work was to evaluate five culture media for the growth and sporulation of one NTCD (Z31) and evaluate the viability of a lyophilized spore solution of NTCD Z31 stored at 4 °C or at 25 °C for 2 years. Reinforced clostridial medium (RCM) and brain heart infusion broth (BHI) provided the highest production of NTCD Z31 spores. In the first 6 months of the storage of the lyophilized solution, a reduction in spore count of approximately 0.3 Log₁₀ CFU/mL was observed; however, no further significant reduction in spore count was observed up to 24 months. No difference in spore concentration was found between the two storage temperatures from 6 to 24 months of storage. The present work showed BHI and RCM to be the best choices for the growth and sporulation of NTCD Z31 and suggested that the spores of NTCD Z31 are stable for up to 2 years under both temperature conditions.

Morphological responses to nitrogen stress deficiency of a new heterotrophic isolated strain of Ebro Delta microbial mats

Microorganisms living in hypersaline microbial mats frequently form consortia under stressful and changing environmental conditions. In this paper, the heterotrophic strain DE2010 from a microalgae consortium (Scenedesmus sp. DE2009) from Ebro Delta microbial mats has been phenotypically and genotypically characterized and identified. In addition, changes in the morphology and biomass of this bacterium in response to nitrogen deficiency stress have been evaluated by correlative light and electron microscopy (CLEM) combining differential interference contrast (DIC) microscopy and transmission electron microscopy (TEM) and scanning electron microscopy (SEM). These isolated bacteria are chemoorganoheterotrophic, gram-negative, and strictly aerobic bacteria that use a variety of amino acids, organic acids, and carbohydrates as carbon and energy sources, and they grow optimally at 27 °C in a pH range of 5 to 9 and tolerate salinity from 0 to 70‰ NaCl. The DNA-sequencing analysis of the 16S rRNA and nudC and fixH genes and the metabolic characterization highlight that strain DE2010 corresponds to the species Ochrobactrum anthropi. Cells are rod shaped, 1-3 μm in length, and 0.5 μm wide, but under deprived nitrogen conditions, cells are less abundant and become more round, reducing their length and area and, consequently, their biomass. An increase in the number of pleomorphic cells is observed in cultures grown without nitrogen using different optical and electron microscopy techniques. In addition, the amplification of the fixH gene confirms that Ochrobactrum anthropi DE2010 has the capacity to fix nitrogen, overcoming N₂-limiting conditions through a nifH-independent mechanism that is still unidentified.

Effect of the Synthetic Bile Salt Analog CamSA on the Hamster Model of Clostridium difficile Infection

Clostridium difficile infection (CDI) is the leading cause of antibiotic-associated diarrhea and has gained worldwide notoriety due to emerging hypervirulent strains and the high incidence of recurrence. We previously reported protection of mice from CDI using the antigerminant bile salt analog CamSA. Here we describe the effects of CamSA in the hamster model of CDI. CamSA treatment of hamsters showed no toxicity and did not affect the richness or diversity of gut microbiota; however, minor changes in community composition were observed. Treatment of C. difficile-challenged hamsters with CamSA doubled the mean time to death, compared to control hamsters. However, CamSA alone was insufficient to prevent CDI in hamsters. CamSA in conjunction with suboptimal concentrations of vancomycin led to complete protection from CDI in 70% of animals. Protected animals remained disease-free at least 30 days postchallenge and showed no signs of colonic tissue damage. In a delayed-treatment model of hamster CDI, CamSA was unable to prevent infection signs and death. These data support a putative model in which CamSA reduces the number of germinating C. difficile spores but does not keep all of the spores from germinating. Vancomycin halts division of any vegetative cells that are able to grow from spores that escape CamSA.

Antimicrobial effect of a combination of herb extract and organic acid against Bacillus subtilis spores

The sporicidal activities of the herbs were investigated to screen for novel antimicrobial substances against Bacillus subtilis spores. The bacterial inactivation effects of ethanol extracts of coriander, caraway, mace at concentrations of 0.5% (w/v) and 1.0-2.5% were about 10- and 100-fold respectively against spores. At pH 5, the antimicrobial activity was about 92%, but at pH 4 the sporicidal activity was particularly high, reducing the spore count by 99.99%. The 0.1-2.5% ethanol extract of herbs adjusted to pH 4-5 exhibited significantly marked deactivation effects, with 3-4 log CFU/mL reductions. The herb-acid combination exerted a further increase in sporicidal activity, with an additional 1-3 log CFU/mL reduction. The sporicidal mechanism was assumed to involve a two-step: (1) the hydrophobic binding of surfactants in the herbs onto the spore coat destroys its protein, and (2) the acid then penetrates into the interior, generating unstable growth conditions.

Psychrosphaera aquimarina sp. nov., a marine bacterium isolated from seawater collected from Asan Bay, Republic of Korea

Cells of strain SW33^T, isolated from the seawater of Asan Bay, Republic of Korea, were characterized as Gram-stain-negative, aerobic, rod-shaped, motile and non-spore-forming. Phylogenetic analysis revealed that strain SW33^T belonged to the genus Psychrosphaera and clustered distantly with the other genera in the family Pseudoalteromonadaceae in the phylogenetic tree. The 16S rRNA sequences of strain SW33^T revealed high similarities to Psychrosphaera saromensis SA4-48^T (98.7 %), Psychrosphaera haliotis KDW4^T (97.4 %) and Psychrosphaera aestuarii PSC101^T (97.3 %). The major fatty acids were C16 : 0 (27.9 %), summed feature 3 (32.2 %) and summed feature 8 (17.2 %). The predominant quinone was Q-8, and the polar lipid profile consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and an unidentified amino lipid. The DNA G+C content was 38.3 mol%. The DNA-DNA relatedness values with the three species of Psychrosphaera saromensis KCTC 23240^T, Psychrosphaera haliotis KCTC 22500^T and Psychrosphaera aestuarii KCTC 32274^T were 22, 23 and 18 %, respectively. Based on the phenotypic characteristics and taxonomic analyses, we propose that strain SW33^T represents a novel species within the genus Psychrosphaera, for which the name Psychrosphaera aquimarina sp. nov. with the type strain SW33^T (=KCTC 52743^T=CICC 24249^T) is proposed.

Paucibacter oligotrophus sp. nov., isolated from fresh water, and emended description of the genus Paucibacter

A Gram-stain-negative, rod-shaped, non-spore forming, motile and strictly oxidative bacterium, strain CHU3T, was isolated from fresh water in the Daecheong Reservoir, South Korea. A comparison of the 16S rRNA gene sequence showed that the novel bacterium is closely related to Paucibacter toxinivorans 2C20T (=KCTC 42569T) with a sequence similarity value of 97.8 %, Pelomonas saccharophila DSM 654T (=KCTC 52256T) with 97.4 % similarity and Pelomonas aquatica CCUG 52575T (=KCTC 42961T) with 97.3 % similarity, respectively. The major fatty acids (>10 %) of the isolate were summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c) and C16 : 0. Ubiquinone-8 was detected as the respiratory quinone. The polar lipids contained diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylserine and an unidentified aminolipid. The DNA G+C content was 62.5 mol%. DNA-DNA hybridization experiments with PaucibactertoxinivoransKCTC 42569T (=2C20T), PelomonassaccharophilaKCTC 52256T (=DSM 654T) and PelomonasaquaticaKCTC 42961T (=CCUG 52575T) resulted in relatedness values of 20 % (reciprocal 11 %), 16 % (reciprocal 17 %) and 15 % (reciprocal 19 %), respectively. The phylogenetic analysis, DNA-DNA hybridization value, polar lipids, fatty acid composition and other physiological characteristics confirmed that strain CHU3T represents a novel species in the genus Paucibacter for which the name Paucibacter oligotrophus sp. nov. is proposed. The type strain is CHU3T (=KCTC 42519T=CICC 24092T). An emended description of the genus Paucibacter is also proposed on the basis of new data obtained in this study.

Microbiological laboratory diagnostics of neglected zoonotic diseases (NZDs)

This review reports on laboratory diagnostic approaches for selected, highly pathogenic neglected zoonotic diseases, i.e. anthrax, bovine tuberculosis, brucellosis, echinococcosis, leishmaniasis, rabies, Taenia solium-associated diseases (neuro-/cysticercosis & taeniasis) and trypanosomiasis. Diagnostic options, including microscopy, culture, matrix-assisted laser-desorption-ionisation time-of-flight mass spectrometry, molecular approaches and serology are introduced. These procedures are critically discussed regarding their diagnostic reliability and state of evaluation. For rare diseases reliable evaluation data are scarce due to the rarity of samples. If bio-safety level 3 is required for cultural growth, but such high standards of laboratory infrastructure are not available, serological and molecular approaches from inactivated sample material might be alternatives. Multiple subsequent testing using various test platforms in a stepwise approach may improve sensitivity and specificity. Cheap and easy to use tests, usually called "rapid diagnostic tests" (RDTs) may impact disease control measures, but should not preclude developing countries from state of the art diagnostics.

Characterization of germination of spores of Clostridium estertheticum, the primary causative agent of blown pack spoilage of vacuum packaged beef

The aim of this study was to investigate the effect of various factors on the germination of Clostridium estertheticum endospores (spores) in relation to beef. The effect of heat on germination was determined by recovering C. estertheticum on Columbia agar from spore suspensions not heated or heated at 63, 70 or 80°C for various times. The effects of pH, temperature and oxygen were determined, by enumeration of remaining ungerminated spores during incubation in Meat Juice medium (MJM). Amino acids and lactate were tested for their ability to trigger germination of C. estertheticum spores by monitoring dipicolinic acid (DPA) release. Heat treatment of spores at 80°C for ≤20min significantly (p<0.05) increased the numbers of spores recovered on blood agar. Neither incubation temperature nor oxygen affected germination in MJM. The optimal pH for germination was 7.0 to 7.5. Incubation with leucine or aspartic acid caused a 1.3% release of DPA, the highest among all amino acids tested. Incubation with lactate resulted in a 4.1% release of DPA, which was significantly (p<0.05) higher than those from incubation with amino acids. The DPA release from incubation with lactate, lactate with amino acids, or MJM was similar (p>0.05).

Sporicidal Activities of Various Surfactant Components against Bacillus subtilis Spores

The sporicidal activities against Bacillus subtilis spores of surfactant components with hydrophilic and hydrophobic properties that can lead to the denaturation of various proteins comprising the spore structure were investigated. The reduction in spore numbers by each of the surfactant components bornyl acetate, geranyl acetate, pinene, p-cymene, camphene, citral, 2,3-dihydrobenzofuran, polylysine, and thiamine dilaurylsulfate at 1% was estimated at 1 to 2 log CFU/ml. The average hydrophilelipophile balance value of surfactants with sporicidal activity causing a reduction of 1 to 2 log CFU/ml was 9.3, with a range from 6.7 to 15.8, which is similar to the values of various chemical surfactants of 9.6 to 16.7. The results also showed that the surfactants that were hydrophobic were more effective than those that were hydrophilic in killing B. subtilis spores. Furthermore, the sporicidal effect of surfactants like geranyl acetate and γ-terpinene was significantly enhanced in the presence of a germinant, because L-alanine and synergistic cofactors (e.g., K(+) ions) trigger cortex hydrolysis in spores.

Fast spore breaking by superheating

Here we present the results of Bacillus subtilis spores breaking using superheating. The spore sample was pumped through the open-ended capillary tube mounted across the heated zone. We investigated the influence of temperature in the range 120-180 °C. The heat exposure was controlled by the length of the heated zone, the inner diameter of the capillary and the sample flow rate. We found that spore treatment above 120 °C resulted in the release of DNA within 20 s.

A thermophilic, hydrogenogenic and carboxydotrophic bacterium, Calderihabitans maritimus gen. nov., sp. nov., from a marine sediment core of an undersea caldera

A hydrogenogenic, carboxydotrophic marine bacterium, strain KKC1(T), was isolated from a sediment core sample taken from a submerged marine caldera. Cells were non-motile, Gram-stain-negative, 1.0-3.0 µm straight rods, often observed with round endospores. Strain KKC1(T) grew at 55-68 °C, pH 5.2-9.2 and 0.8-14 % (w/v) salinity. Optimum growth occurred at 65 °C, pH 7.0-7.5 and 2.46 % salinity with a doubling time of 3.7 h. The isolate grew chemolithotrophically, producing H2 from carbon monoxide (CO) oxidation with reduction of various electron acceptors, e.g. sulfite, thiosulfate, fumarate, ferric iron and AQDS (9,10-anthraquinone 2,6-disulfonate). KKC1(T) grew heterotrophically on pyruvate, lactate, fumarate, glucose, fructose and mannose with thiosulfate as an electron acceptor. When grown mixotrophically on CO and pyruvate, C16 : 0 constituted almost half of the total cellular fatty acids. The DNA G+C content was 50.6 mol%. The 16S rRNA gene sequence of KKC1(T) was most closely related to those of members of the genus Moorella with similarity ranging from 91 to 89 %. Based on physiological and phylogenetic novelty, we propose the isolate as a representative of a new genus and novel species with the name Calderihabitans maritimus gen. nov., sp. nov.; the type strain of the type species is KKC1(T) ( = DSM 26464(T) = NBRC 109353(T)).

A new strategy for the prevention of Clostridium difficile infection

BACKGROUND

Clostridium difficile infection (CDI) is a leading cause of antibiotic-associated diarrhea. The infective form of C. difficile is the spore, but the vegetative bacterium causes the disease. Because C. difficile spore germination is required for symptomatic infection, antigermination approaches could lead to the prevention of CDI. We recently reported that CamSA, a bile salt analog, inhibits C. difficile spore germination in vitro.

METHODS

Mice infected with massive inocula of C. difficile spores were treated with different concentrations of CamSA and monitored for CDI signs. C. difficile spore and vegetative cells were counted in feces from infected mice.

RESULTS

A single 50-mg/kg dose of CamSA prevented CDI in mice without any observable toxicity. Lower CamSA doses resulted in delayed CDI onset and less severe signs of disease. Ingested C. difficile spores were quantitatively recovered from feces of CamSA-protected mice.

CONCLUSIONS

Our results support a mechanism whereby the antigermination effect of CamSA is responsible for preventing CDI signs. This approach represents a new paradigm in CDI treatment. Instead of further compromising the microbiota of CDI patients with strong antibiotics, antigermination therapy could serve as a microbiota surrogate to curtail C. difficile colonization of antibiotic-treated patients.

Activate to eradicate: inhibition of Clostridium difficile spore outgrowth by the synergistic effects of osmotic activation and nisin

BACKGROUND

Germination is the irreversible loss of spore-specific properties prior to outgrowth. Because germinating spores become more susceptible to killing by stressors, induction of germination has been proposed as a spore control strategy. However, this strategy is limited by superdormant spores that remain unaffected by germinants. Harsh chemicals and heat activation are effective for stimulating germination of superdormant spores but are impractical for use in a hospital setting, where Clostridium difficile spores present a challenge. Here, we tested whether osmotic activation solutes will provide a mild alternative for stimulation of superdormant C. difficile spores in the presence of germinants as previously demonstrated in several species of Bacillus. In addition, we tested the hypothesis that the limitations of superdormancy can be circumvented with a combined approach using nisin, a FDA-approved safe bacteriocin, to inhibit outgrowth of germinated spores and osmotic activation solutes to enhance outgrowth inhibition by stimulating superdormant spores.

PRINCIPAL FINDINGS

Exposure to germination solution triggered ~1 log(10) colony forming units (CFU) of spores to germinate, and heat activation increased the spores that germinated to >2.5 log(10)CFU. Germinating spores, in contrast to dormant spores, became susceptible to inhibition by nisin. The presence of osmotic activation solutes did not stimulate germination of superdormant C. difficile spores exposed to germination solution. But, in the absence of germination solution, osmotic activation solutes enhanced nisin inhibition of superdormant spores to >3.5 log(10)CFU. The synergistic effects of osmotic activation solutes and nisin were associated with loss of membrane integrity.

CONCLUSIONS

These findings suggest that the synergistic effects of osmotic activation and nisin bypass the limitations of germination as a spore control strategy, and might be a novel method to safely and effectively reduce the burden of C.difficile spores on skin and environmental surfaces.

Inhibition of Escherichia coli O157:H7 and Clostridium sporogenes in spinach packaged in modified atmospheres after treatment combined with chlorine and lactic acid bacteria

Implementation of modified atmospheric packaging (MAP) into retail produce is a less commonly practiced method due to differences among commodities and the potential growth of anaerobes. Pathogens including Escherichia coli O157:H7 have been responsible for spinach outbreaks across the United States. In this study, hurdles, including those currently used with produce safety, such as MAP and chlorine, were combined with lactic acid bacteria (LAB) to inhibit pathogens. Spinach was coinoculated with E. coli O157:H7 and Clostridium sporogenes, a surrogate for C. botulinum, and treated with water or a hurdle that included water, chlorine, and LAB. Spinach from treatments were packaged in air (traditional), oxygen (80% O₂, 20% CO₂), or nitrogen (80% N₂, 20% CO₂) and stored in a retail display case for 9 d at 4 to 7 °C. The hurdle inhibited E. coli O157:H7 and C. sporogenes compared to controls with reductions of 1.43 and 1.10 log (P < 0.05), respectively. The nitrogen atmosphere was outperformed by air and oxygen in the reduction of E. coli O157:H7 (P < 0.05) with a decrease of 0.26 and 0.15 logs. There were no significant differences among the 3 atmospheres on C. sporogenes survival. Relative to these hurdles, we also chose to evaluate the potential benefits of LAB in pathogen control. The survival of LAB in interventions demonstrates implementation of LAB into produce could control pathogens, without damaging produce or altering organoleptic properties.

PRACTICAL APPLICATION

The goal of our work was to identify methods that could reduce food-borne pathogens in packaged spinach products. Using current industry techniques in combination with unique methods, such as the use of beneficial bacteria, our research identified whether harmful microorganisms could be eliminated. Our data demonstrate that specific packaging conditions with beneficial bacteria can help eliminate or reduce the survival of E. coli O157:H7 and C. sporogenes (a model for C. botulinum) in produce.

Activity of RBx 11760, a novel biaryl oxazolidinone, against Clostridium difficile

OBJECTIVES

RBx 11760, a novel oxazolidinone, was investigated for in vitro and in vivo activity against Clostridium difficile.

METHODS

The in vitro activity of RBx 11760 and three other agents against 50 diverse C. difficile clinical isolates and other obligate anaerobic bacteria was determined. The effect of RBx 11760 on sporulation and toxin production was determined against different C. difficile isolates. We used a hamster infection model to investigate the efficacy of RBx 11760, vancomycin and metronidazole. The mechanism of action of RBx 11760 against C. difficile ATCC 43255 was determined by macromolecular synthesis inhibition.

RESULTS

RBx 11760 MICs were in the range of 0.5-1 mg/L for C. difficile isolates, and it demonstrated concentration-dependent killing of C. difficile ATCC 43255 and C. difficile 6387 up to 2-4× MIC (1-2 mg/L). RBx 11760, at concentrations as low as 0.25-0.5 mg/L, resulted in a significant reduction in de novo toxin production as well as sporulation in different C. difficile isolates. In contrast, vancomycin, metronidazole and linezolid had little or no effect on toxin production and appeared to promote the formation of spores. In the hamster infection model, treatment with RBx 11760 resulted in prolonged survival of animals as compared with vancomycin or metronidazole, which correlated well with the histopathology results. Macromolecular labelling results suggest that RBx 11760 is a potent inhibitor of bacterial protein synthesis.

CONCLUSIONS

RBx 11760 showed excellent in vitro and in vivo activity against C. difficile, and it could be a promising novel candidate for future drug development against C. difficile infection.

Microwave inactivation of Bacillus atrophaeus spores in healthcare waste

Public healthcare wastes from the region of Ribeirão Preto, Brazil, pre-sterilized in an autoclave, were inoculated with spores of Bacillus atrophaeus for microwave processing on a laboratory scale. The influence of waste moisture (40%, 50% and 60% wet basis), presence of surfactant, power per unit mass of waste (100, 150 and 200 W/kg) and radiation exposure time (from 5 to 40 min) on the heating curves was investigated. The most favorable conditions for waste heating with respect to moisture and use of surfactant were then applied in an experimental analysis of the degree of inactivation of B. atrophaeus spores as a function of time and power per unit mass of waste. Based on Chick's and Arrhenius laws, the experimental results were adjusted by the least squares method to determine the activation energies (9203-5782 J/mol) and the Arrhenius pre-exponential factor (0.23 min(-1)). The kinetic parameters thus obtained enabled us to predict the degree of inactivation achieved for B. atrophaeus spores in typical healthcare waste. The activation energy was found to decrease as the power per waste mass increased, leading to the conclusion that, in addition to the thermal effect on the inactivation of B. atrophaeus spores, there was an effect inherent to radiation.

Triggering germination represents a novel strategy to enhance killing of Clostridium difficile spores

Background

Clostridium difficile is an anaerobic, spore-forming bacterium that is the most common cause of healthcare-associated diarrhea in developed countries. Control of C. difficile is challenging because the spores are resistant to killing by alcohol-based hand hygiene products, antimicrobial soaps, and most disinfectants. Although initiation of germination has been shown to increase susceptibility of spores of other bacterial species to radiation and heat, it was not known if triggering of germination could be a useful strategy to increase susceptibility of C. difficile spores to radiation or other stressors.

Principal Findings

Here, we demonstrated that exposure of dormant C. difficile spores to a germination solution containing amino acids, minerals, and taurocholic acid resulted in initiation of germination in room air. Germination of spores in room air resulted in significantly enhanced killing by ultraviolet-C (UV-C) radiation and heat. On surfaces in hospital rooms, application of germination solution resulted in enhanced eradication of spores by UV-C administered by an automated room decontamination device. Initiation of germination under anaerobic, but not aerobic, conditions resulted in increased susceptibility to killing by ethanol, suggesting that exposure to oxygen might prevent spores from progressing fully to outgrowth. Stimulation of germination also resulted in reduced survival of spores on surfaces in room air, possibly due to increased susceptibility to stressors such as oxygen and desiccation.

Conclusions

Taken together, these data demonstrate that stimulation of germination could represent a novel method to enhance killing of spores by UV-C, and suggest the possible application of this strategy as a means to enhance killing by other agents.

Protection Afforded by Fluoroquinolones in Animal Models of Respiratory Infections with Bacillus anthracis, Yersinia pestis, and Francisella tularensis

Successful treatment of inhalation anthrax, pneumonic plague and tularemia can be achieved with fluoroquinolone antibiotics, such as ciprofloxacin and levofloxacin, and initiation of treatment is most effective when administered as soon as possible following exposure. Bacillus anthracis Ames, Yersinia pestis CO92, and Francisella tularensis SCHU S4 have equivalent susceptibility in vitro to ciprofloxacin and levofloxacin (minimal inhibitory concentration is 0.03 μg/ml); however, limited information is available regarding in vivo susceptibility of these infectious agents to the fluoroquinolone antibiotics in small animal models. Mice, guinea pig, and rabbit models have been developed to evaluate the protective efficacy of antibiotic therapy against these life-threatening infections. Our results indicated that doses of ciprofloxacin and levofloxacin required to protect mice against inhalation anthrax were approximately 18-fold higher than the doses of levofloxacin required to protect against pneumonic plague and tularemia. Further, the critical period following aerosol exposure of mice to either B. anthracis spores or Y. pestis was 24 h, while mice challenged with F. tularensis could be effectively protected when treatment was delayed for as long as 72 h postchallenge. In addition, it was apparent that prolonged antibiotic treatment was important in the effective treatment of inhalation anthrax in mice, but short-term treatment of mice with pneumonic plague or tularemia infections were usually successful. These results provide effective antibiotic dosages in mice, guinea pigs, and rabbits and lay the foundation for the development and evaluation of combinational treatment modalities.

Requirements for germination of Clostridium sordellii spores in vitro

Clostridium sordellii is a spore-forming, obligately anaerobic, Gram-positive bacterium that can cause toxic shock syndrome after gynecological procedures. Although the incidence of C. sordellii infection is low, it is fatal in most cases. Since spore germination is believed to be the first step in the establishment of Bacilli and Clostridia infections, we analyzed the requirements for C. sordellii spore germination in vitro. Our data showed that C. sordellii spores require three structurally different amino acids and bicarbonate for maximum germination. Unlike the case for Bacilli species, d-alanine had no effect on C. sordellii spore germination. C. sordellii spores germinated only in a narrow pH range between 5.7 and 6.5. In contrast, C. sordellii spore germination was significantly less sensitive to temperature changes than that of the Bacilli. The analysis of the kinetics of C. sordellii spore germination showed strong allosteric behavior in the binding of l-phenylalanine and l-alanine but not in that of bicarbonate or l-arginine. By comparing germinant apparent binding affinities to their known in vivo concentrations, we postulated a mechanism for differential C. sordellii spore activation in the female reproductive tract.

Bacillus cereus spores release alanine that synergizes with inosine to promote germination

BACKGROUND

The first step of the bacterial lifecycle is the germination of bacterial spores into their vegetative form, which requires the presence of specific nutrients. In contrast to closely related Bacillus anthracis spores, Bacillus cereus spores germinate in the presence of a single germinant, inosine, yet with a significant lag period.

METHODS AND FINDINGS

We found that the initial lag period of inosine-treated germination of B. cereus spores disappeared in the presence of supernatants derived from already germinated spores. The lag period also dissipated when inosine was supplemented with the co-germinator alanine. In fact, HPLC-based analysis revealed the presence of amino acids in the supernatant of germinated B. cereus spores. The released amino acids included alanine in concentrations sufficient to promote rapid germination of inosine-treated spores. The alanine racemase inhibitor D-cycloserine enhanced germination of B. cereus spores, presumably by increasing the L-alanine concentration in the supernatant. Moreover, we found that B. cereus spores lacking the germination receptors gerI and gerQ did not germinate and release amino acids in the presence of inosine. These mutant spores, however, germinated efficiently when inosine was supplemented with alanine. Finally, removal of released amino acids in a washout experiment abrogated inosine-mediated germination of B. cereus spores.

CONCLUSIONS

We found that the single germinant inosine is able to trigger a two-tier mechanism for inosine-mediated germination of B. cereus spores: Inosine mediates the release of alanine, an essential step to complete the germination process. Therefore, B. cereus spores appear to have developed a unique quorum-sensing feedback mechanism to monitor spore density and to coordinate germination.