Bacteriocin-like inhibitor substances produced by Mexican strains of Bacillus thuringiensis

Bacillus cereus sensu lato antimicrobial arsenal: An overview

The Bacillus cereus group contains genetically closed bacteria displaying a variety of phenotypic features and lifestyles. The group is mainly known through the properties of three major species: the entomopathogen Bacillus thuringiensis, the animal and human pathogen Bacillus anthracis and the foodborne opportunistic strains of B. cereus sensu stricto. Yet, the actual diversity of the group is far broader and includes multiple lifestyles. Another less-appreciated aspect of B. cereus members lies within their antimicrobial potential which deserves consideration in the context of growing emergence of resistance to antibiotics and pesticides, and makes it crucial to find new sources of antimicrobial molecules. This review presents the state of knowledge on the known antimicrobial compounds of the B. cereus group members, which are grouped according to their chemical features and biosynthetic pathways. The objective is to provide a comprehensive review of the antimicrobial range exhibited by this group of bacteria, underscoring the interest in its potent biocontrol arsenal and encouraging further research in this regard.

Enhanced production of bacteriocin by Bacillus subtilis ZY05

Bacteriocin-producing strains were isolated from the soil of the rice field, screened out using an agar-well diffusion assay against six indicator bacterial strains, and the highest among them was selected for further investigation. The study focuses on how different growing conditions affect bacteriocin production. One-parameter-at-a-time (OPAT) and a central composite design of response surface methodology (RSM) were used to perform the optimization in two steps. In the OPAT trials, bacteriocin synthesis was elevated by 29%, 45%, and 34%, by employing sucrose as a carbon source and changing the NaCl concentration and pH at 7, respectively. To determine the linear, squared, and interaction correlations among the process variables to predict the ideal conditions for production, a four-factor central composite design (CCD) of RSM was used. It was determined that the analysis of variance (ANOVA), which produces a recognized model using RSM, is sufficient to describe bacteriocin production regarding activity (R2 = 0.9606). The ideal conditions for increased production were 1.51% sucrose concentration, 1.59% NaCl concentration, pH 6.35, and 28.66 (about 29) hours of incubation. The value predicted by RSM (4051.55 AU/mL) was approximately two times greater than the value of a non-optimized medium. The experimental value of 4403.85 AU/mL was closer to the expected value. According to the data, increasing bacteriocin activity required employing the ideal sucrose concentration, NaCl concentration, and incubation time. The partially purified bacteriocin was found stable at temperatures between 24 and 50 °C and at pH 5-8. The molecular weight purified bacteriocin was determined to be between 13 and 35 kDa.

Drug-Resistant Proteus Virulence Factors Characterization and Their Inhibition Using Probiotic Bacteria

Background: The genus Proteus is a Gram-negative bacterium with a unique characteristic of swarming. Mainly three species are involved in initiating urinary tract infections in the community and in immunocompromised patients, particularly in patients going through long-term catheterization. Due to their strong virulence factors like biofilm formations, protease, and hemolysin, they can lead to lengthening infections in affected individuals. Probiotics are live bacteria and yeasts that are beneficial to human health and can be used as an alternative for the control of nosocomial diseases. Lactobacilli are one of the common probiotics mostly found in yogurt and other fermented foods that have been used as a substitute for infection control. Objectives: The current study was designed to screen potential probiotic bacteria to encounter antibiotic-resistant and virulent Proteus species. Methods: In the current study, using probiotics, already known antibiotic-resistant isolates (n = 25) of Proteus were processed to characterize their virulence factors and their inhibition. Biofilm formation, protease, and hemolysin activities were studied using different phenotypic detection methods. Further, their virulence genes zapA, flg, hmpA, mrp, and rsbA were explored using their genomic DNA. These isolates were found resistant to different classes of antibiotics, and a strategy was designed to inhibit their growth by using probiotic bacteria isolated from the soil. Results: Virulence factors first, all isolates were subjected to biofilm detection, and they were 32% (n = 8) strong, 40% (n = 10) moderate, 16% (n = 4) weak, and 12% (n = 3) non-biofilm producers. All isolates were positive for swarming activity by showing a differentiated ring form of growth. Protease activity showed 56% (n = 14) isolates. Only 24% (n = 6) of isolates were positive for hemolysin. Virulence factors and molecular mechanisms were studied, and gene rsbA responsible for swarming was amplified in 17 (68%) Proteus isolates, and mrp responsible for fimbria was detected in 19 (76%) bacterial isolates. Further, these isolates were subjected to flagella, protease, and hemolysin, and it was revealed that flg 11 (44%), 13 (52%) protease coding zapA, and hmA gene coding hemolysin were amplified in 2 (8%) Proteus isolates. Probiotic bacteria isolated from soil samples were probed for antagonistic activity against Proteus species. The probiotic bacteria were identified as Lactobacillus plantarum, Bacillus subtilis, and B. licheniformis. Due to their strong growth inhibitory effects against Proteus, it is crucial to characterize further the metabolites that have shown suppressive results against Proteus. Conclusions: Findings from the current study will provide new avenues for drug development and also help clinicians manage resistant pathogens in healthcare settings. Probiotic applications for infection control can be useful in treating resistant pathogens. Further purification and characterization of metabolites will provide alternative options for managing resistance issues in microbes.

Evaluation of inhibitory compounds produced by bacteria isolated from a hydrogen-producing bioreactor during the self-fermentation of wheat straw

AIMS

The objective of this study was to evaluate the inhibitory activity of compounds secreted by bacteria isolated from a hydrogen-producing bioreactor to understand how these microorganisms interact in this community.

METHODS AND RESULTS

In vitro inhibitory assays were performed using samples secreted by bacteria subject to different treatments to determine if their inhibitory effect was due to organic acids, non-proteinaceous compounds, or bacteriocin-like inhibitory substances (BLIS). Bacterial isolated were suppressed 43%, 30%, and 27% by neutralized, precipitated, and non-neutralized cell-free supernatants, respectively. Non-hydrogen producers (Non-H₂ P) LAB (Lactobacillus plantarum LB1, L. pentosus LB7, Pediococcus acidilactici LB4) and hydrogen producers (H₂ P) LAB (Enterococcus faecium F) were inhibited by the production of organic acids, non-proteinaceous compounds, and BLIS. Meanwhile, the obligate anaerobe H₂ P (Clostridium beijerinckii B) inhibited by the production of non-proteinaceous compounds and BLIS. The presence of BLIS was confirmed when proteolytic enzymes affected the inhibitory activity of secreted proteins in values ranging from 20 to 42%. The BLIS produced by L. plantarum LB1, P. acidilactici LB4, L. pentosus LB7, and E. faecium F showed molecular masses of ~ 11 kDa, 25 kDa, 20 kDa, and 11 kDa, respectively.

CONCLUSIONS

It was demonstrated antagonistic interactions between Lactobacillus- Enterococcus, and Pediococcus-Enterococcus species, generated by the secretion of organic acids, non-proteinaceous compounds, and BLIS.

SIGNIFICANCE AND IMPACT OF THE STUDY

We report the interactions between LAB isolated from hydrogen-producing bioreactors. These interactions might impact the dynamics of the microbial population during hydrogen generation. Our work lays a foundation for strategies that allow controlling bacteria that can affect hydrogen production.

Thurincin H Is a Nonhemolytic Bacteriocin of Bacillus thuringiensis with Potential for Applied Use

Thurincin H, a bacteriocin produced by Bacillus thuringiensis, exhibits antibacterial activity against Gram-positive and Gram-negative bacteria. While much is known about its expression and antimicrobial spectrum, its hemolytic property has yet to be established. In this study, thurincin H was produced in a plasmid-free acrystalliferous strain of B. thuringiensis (Bt Cry^-B) that naturally lacked antimicrobial and hemolytic activities. When grown in Tryptic Soy Broth (TSB), the bacteriocin's maximal production in Bt Cry^-B harboring the thurincin H genetic cluster (Bt Cry^-B/pThur) was observed at 24 h. Thurincin H was purified as a sole peptide of ~5 kDa using three purification steps, i.e., salt precipitation, ultrafiltration, and gel filtration chromatography. The bacteriocin showed inhibitory activity against B. cereus (5631 U), Bt Cry^-B (8827 U), E. faecium wild type (11,197 U), and E. faecium ATCC 19,434 (6950 U), but not against Bt Cry^-B/pThurH and Bt Cry^-B/pThurHΔThnA. In addition, a minimum inhibitory concentration (MIC) of 5.0 μg/mL against B. cereus 183 was observed. In silico predictions suggested that thuricin H lacks hemolytic activity, which was validated in vitro using 4 × the MIC, i.e., 20 μg/ml. Our data lay a foundation for the potential safe use of thurincin H as an antibacterial peptide for medical use, in food products, and for expression in probiotic bacteria.

In vitro and in silico approach for characterization of antimicrobial peptides from potential probiotic cultures against Staphylococcus aureus and Escherichia coli

The focus of the present study was to characterize antimicrobial peptide produced by potential probiotic cultures of Enterococcus durans DB-1aa (MCC4243), Lactiplantibacillus plantarum Cu2-PM7 (MCC4246) and Limosilactobacillus fermentum Cu3-PM8 (MCC4233) against Staphylococus aureus MTCC 96 and Escherichia coli MTCC118. The growth kinetic assay revealed 24 h of incubation to be optimum for bacteriocin production. The partially purified compound of all the three selected cultures after ion-exchange chromatography was found to be thermoresistant and stable under a wide range of pH. The compound was sensitive to proteinase-K, but resistant to trypsin, α-amylase and lipase. Comparatively, bacteriocins from L. fermentum Cu3-PM8 and L. plantarum Cu2-PM7 showed higher stability under studied parameter, hence was taken up for further investigation. The apparent molecular weight of bacteriocin from L. fermentum MCC4233 and L. plantarum MCC4246 was found to be 3.5 kDa. Further, plantaricin gene from MCC4246 was characterized in silico. The translated partial amino acid sequence of the plnA gene in MCC4246 displayed 48 amino acids showing 100 % similarity with plantaricin A of Lactobacillus plantarum (WP_0036419). The sequence revealed 7 β sheets, 6 α sheets, 6 predicted coils and 9 predicted turns. The predicted properties of the peptide included an isoelectric point of 10.82 and a hydrophobicity of 48.6 %. The molecular approach of using Geneious Prime software and protein prediction data base for characterization of bacteriocin is novel and predicts "KSSAYSLQMGATAIKQVKKLFKKWGW" to be a peptide responsible for antimicrobial activity. The study provides information about a broad spectrum bacteriocin in native probiotic culture and paves a way towards its application in functional foods as a biopreservative agent.

Purification, characterization, and mode of action of Paracin 54, a novel bacteriocin against Staphylococci

Staphylococci belong to conditionally pathogenic bacteria, and the pathogenicity of Staphylococcus aureus is the strongest among them. Enterotoxin produced by it can contaminate food and cause food poisoning. Bacteriocin is a kind of polypeptide with antibacterial activity synthesized by some bacteria during metabolism. In this study, we report on purification, characterization, and mode of action of the bacteriocin named Paracin 54, produced by Lactobacillus paracasei ZFM54. Paracin 54 was purified by precipitation with 80% ammonium sulfate, strong cation-exchange chromatography, G-25 gel column, and reversed-phase high-performance liquid chromatography (HPLC). The molecular weight of Paracin 54 (5718.1843 Da) was determined by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Paracin 54 showed broad-spectrum inhibitory activity. It had a strong inhibitory effect on Staphylococci with minimum inhibitory concentration values of 3.00-4.50 μg/mL. Paracin 54 was heat-stable and active only in acidic pH range (2-6). After treatment with proteases, the activity was lost. The results of mode of action showed Paracin 54 damaged the cell membrane and cell wall of Staphylococcus aureus, and then the cytoplasm leaked out, leading to death of the bacteria. These properties make Paracin 54 a promising candidate to prevent the growth of spoilage bacteria and control food poisoning caused by Staphylococci. KEY POINTS: • Paracin 54 was purified from Lactobacillus paracasei ZFM54 with good biochemical characteristics. • Paracin 54 had a strong effect against Staphylococci, making it a promising preservative to prevent the growth of Staphylococci in food. • The mode of action of Paracin 54 on Staphylococcus aureus was revealed.

The duo Clostridium and Lactobacillus linked to hydrogen production from a lignocellulosic substrate

The study aimed to identify interspecies interactions within a native microbial community present in a hydrogen-producing bioreactor fed with two wheat straw cultivars. The relationships between the microbial community members were studied building a canonical correspondence analysis and corroborated through in vitro assays. The results showed that the bioreactor reached a stable hydrogen production of ca. 86 mL/kg·d in which the cultivar change did not affect the average performance. Lactobacillus and Clostridium dominated throughout the whole operation period where butyric acid was the main metabolite. A canonical correspondence analysis correlated positively Lactobacillus with hydrogen productivity and hydrogen-producing bacteria like Clostridium and Ruminococaceae. Agar diffusion testing of isolated strains confirmed that Lactobacillus inhibited the growth of Enterococcus, but not of Clostridium. We suggest that the positive interaction between Lactobacillus and Clostridium is generated by a division of labor for degrading the lignocellulosic substrate in which Lactobacillus produces lactic acid from the sugar fermentation while Clostridium quickly uses this lactic acid to produce hydrogen and butyric acid. The significance of this work lies in the fact that different methodological approaches confirm a positive association in the duo Lactobacillus-Clostridium in a bioreactor with stable hydrogen production from a complex substrate.

Bacillus sp. Bacteriocins: Natural Weapons against Bacterial Enemies

BACKGROUND

Currently, antibiotic-resistant pathogenic bacteria are emerging as an important health problem worldwide. The search for new compounds with antibiotic characteristics is the most promising alternative. Bacteriocins are natural compounds that are inhibitory against pathogens, and Bacillus species are the major producers of these compounds, which have shown antimicrobial activity against clinically important bacteria. These peptides not only have potential in the pharmaceutical industry but also in food and agricultural sectors.

OBJECTIVE

We provide an overview of the recent bacteriocins isolated from different species of Bacillus including their applications and the older bacteriocins.

RESULTS

In this review, we have revised some works about the improvements carried out in the production of bacteriocins.

CONCLUSION

These applications make bacteriocins very promising compounds that need to study for industrial production.

Dissecting the Environmental Consequences of Bacillus thuringiensis Application for Natural Ecosystems

Bacillus thuringiensis (Bt), a natural pathogen of different invertebrates, primarily insects, is widely used as a biological control agent. While Bt-based preparations are claimed to be safe for non-target organisms due to the immense host specificity of the bacterium, the growing evidence witnesses the distant consequences of their application for natural communities. For instance, upon introduction to soil habitats, Bt strains can affect indigenous microorganisms, such as bacteria and fungi, and further establish complex relationships with local plants, ranging from a mostly beneficial demeanor, to pathogenesis-like plant colonization. By exerting a direct effect on target insects, Bt can indirectly affect other organisms in the food chain. Furthermore, they can also exert an off-target activity on various soil and terrestrial invertebrates, and the frequent acquisition of virulence factors unrelated to major insecticidal toxins can extend the Bt host range to vertebrates, including humans. Even in the absence of direct detrimental effects, the exposure to Bt treatment may affect non-target organisms by reducing prey base and its nutritional value, resulting in delayed alleviation of their viability. The immense phenotypic plasticity of Bt strains, coupled with the complexity of ecological relationships they can engage in, indicates that further assessment of future Bt-based pesticides' safety should consider multiple levels of ecosystem organization and extend to a wide variety of their inhabitants.

Alternative Anti-Infective Treatments to Traditional Antibiotherapy against Staphylococcal Veterinary Pathogens

The genus Staphylococcus encompasses many species that may be pathogenic to both humans and farm animals. These bacteria have the potential to acquire multiple resistant traits to the antimicrobials currently used in the veterinary or medical settings. These pathogens may commonly cause zoonoses, and the infections they cause are becoming difficult to treat due to antimicrobial resistance. Therefore, the development of novel alternative treatments to traditional antibiotherapy has gained interest in recent years. Here, we reviewed the most promising therapeutic strategies developed to control staphylococcal infections in the veterinary field to overcome antibiotic resistance.

Improving the yields of thurincin H in a native producer strain

Thurincin H is a bacteriocin produced by Bacillus thuringiensis with activity against a wide range of bacteria, including Gram positive and Gram negative. Disadvantages of producing thurincin H in B. thuringiensis is the low production level in the native strain probably due to the highly regulated mechanism of biosynthesis. The present study aimed to increase the synthesis of thurincin H produced by the native strain (Btm) through the establishment of additional copies of the structural gene (i.e. thnA) and the genes responsible for the bacterial self-immunity (thnRDE). Here, three recombinant strains of Btm were generated, harboring three, six and nine additional copies of thnA, and three with one copy of thnRDE upstream to the thnA copies. Data showed that the highest yield was obtained at 16 h using three additional copies of thnA (Btm/pHT-One) with a bacteriocin activity of 20,000 U/mg compared with the parental strain which showed 10,000 U/mg, increase of 100% in the production of the bacteriocin. Also, the addition of the genes responsible for self-immunity showed that recombinant B. thuringiensis (Btm/pHT-TwoRDE) can support six additional copies of thnA with an increase of 60% compared with the parental strain.

Class I defensins (BraDef) from broccoli (Brassica oleracea var. italica) seeds and their antimicrobial activity

The objective of this study was to determine whether seeds of Brassica oleracea var. italica (i.e. broccoli, an edible plant) produce defensins that inhibit phytopathogenic fungi and pathogenic bacteria of clinical significance. Crude extracts obtained from broccoli seeds were fractioned by molecular exclusion techniques and analyzed by liquid chromatography-high-resolution mass spectrometry. Two peptides were identified, BraDef1 (10.68 kDa) and BraDef2 (9.9 kDa), which were categorized as Class I defensins based on (a) their primary structure, (b) the presence of four putative cysteine disulfide bridges, and (c) molecular modeling predictions. BraDef1 and BraDef2 show identities of, respectively, 98 and 71%, and 67 and 85%, with defensins from Brassica napus and Arabidopsis thaliana. BraDef (BraDef1 + BraDef2) disrupted membranes of Colletotrichum gloeosporioides and Alternaria alternata and also reduced hyphal growth of C. gloeosporioides by ~ 56% after 120 h of incubation. Pathogenic bacteria (Bacillus cereus 183, Listeria monocytogenes, Salmonella typhimurium, Pseudomonas aeruginosa, and Vibrio parahaemolitycus) were susceptible to BraDef, but probiotic bacteria such as Bifidobacterium animalis, Lactobacillus acidophilus, and Lactobacillus casei were not inhibited. To our knowledge, this is the first report of defensins present in seeds of B. oleracea var. italica (i.e. edible broccoli). Our findings suggest an applied value for BraDef1/BraDef2 in controlling phytopathogenic fungi and pathogenic bacteria of clinical significance.

New bacteriocin-like substances produced by Streptomyces species with activity against pathogens

Streptomyces spp. are Gram-positive bacteria well-known for their ability to produce antibiotics and other metabolites, but few studies on bacteriocins produced by these bacteria have been reported. We tested eight Streptomyces strains against different pathogenic bacteria, and selected S. griseus, S. nigrescens, S. bottroprensis, and S. violaceoruber for further study based on their inhibitory effects against bacteria, including human pathogens. S. bottropensis reached its highest activity at 312 h and was higher than the activities of S. violaceoruber and S. nigrescens. The best condition for bacteriocin precipitation was using diammonium sulfate at 50% saturation. Bacteriocins were susceptible to proteinase treatments and stable at high temperature (up to 100 °C). The highest inhibitory activities were observed between pH 5 and 6. Cross-activity assays indicated that each Streptomyces strain produced different bacteriocins. When preparations of S. griseus and S. nigrescens were subjected to SDS-PAGE, bands of inhibition were observed in the gel overlay assay at a position corresponding to ~ 2 and 3 kDa, respectively, suggesting that both strains are potential sources for novel bacteriocins.

Identification and partial purification of thuricin 4AJ1 produced by Bacillus thuringiensis

Thuricin 4AJ1, produced by Bacillus thuringiensis strain 4AJ1, showed inhibition activity against Bacillus cereus 0938 and ATCC 10987. It began to appear in the stationary phase and reached its maximum activity level of 209.958 U at 18 h against B. cereus 0938 and 285.689 U at 24 h against B. cereus ATCC 10987. Tricine-SDS-PAGE results showed that the partly purified thuricin 4AJ1 was about 6.5 kDa. The molecular weights of the known B. thuringiensis bacteriocins and the ones obtained by the two mainstream websites for predicting bacteriocins were inconsistent with the size of the thuricin 4AJ1, indicating that the bacteriocin obtained in this study may have a novel structure. Based on the biochemical properties, the thuricin 4AJ1 activities increased after treatment with proteinase K and lipase II, and were not affected by a-amylase, catalase, α-chymotrypsin VII and α-chymotrypsin II. It was heat tolerant, being active up to 90º C. In the pH 3-10 range, it maintained most of its activity. Finally, the sensitivity of the strain 4AJ1 to commonly used antibiotics was tested. In view of its stability and antibacterial activity, thuricin 4AJ1 may be applied as a food biopreservative.

Burkholderia pseudomallei-absent soil bacterial community results in secondary metabolites that kill this pathogen

Burkholderia pseudomallei is a Gram-negative bacterium found in soil and the causative agent of a severe disease in humans and animals known as melioidosis. It is intrinsically resistant to many antibiotics and has been reported resistant to the drugs of choice; ceftazidime. Microbial communities in soil in the presence and absence of B. pseudomallei were investigated using metagenomics approach. The variation in bacterial species diversity was significantly higher in soil samples without B. pseudomallei. Abundances of phyla Actinobacteria and Firmicutes were found significantly higher in B. pseudomallei-negative soils. Bacillus amyloliquefaciens KKU1 in phylum Firmicutes was discovered from negative soil and its secondary metabolites could inhibit clinical, environmental and drug resistant isolates of B. pseudomallei, together with some pathogenic Gram-negative but not Gram-positive bacteria. The antimicrobial activity from KKU 1 against B. pseudomallei was abolished when treated with proteinase K, stable in a wide range of pH and remained active after heating at 100 °C for 15 min. Precipitated proteins from KKU1 were demonstrated to cause lysis and corrugated surfaces of B. pseudomallei. The minimum inhibitory concentrations and minimum bactericidal concentrations of the precipitated proteins from KKU1 against B. pseudomallei were 0.97 μg/ml and 3.9 μg/ml. Interestingly, Native SDS-PAGE showed small active compounds of less than 6 kDa, along with other information collectively suggesting the properties of antimicrobial peptides. For the first time, culture-independent information in melioidosis endemic area could lead to a suspected source of metabolites that may help defense against B. pseudomallei and other pathogenic Gram-negative bacteria.

Preliminary studies on the inhibition potential of Indian domestic curd against coliforms, an emerging periodontal pathogen

Background:

Coliforms colonize in dental plaques via oral route and may lead to systemic complications. Escherichia coli and its lipopolysaccharide-induced periodontitis is an emerging threat. Clinical management necessitates antibiotic regimens with risk of resistance and upsetting the gut. There is urgent need for better, sustainable, and economical alternative.

Aim:

To investigate the inhibition of coliforms, a potential periodontopathogen directly by Indian domestic curd (IDC) “in situ".

Materials and Methods:

Coliforms from natural habitat (Municipal sewage in Agartala, Tripura), a source of infection through food and water, were used as target organism. Domestically prepared curd without any fortification is used to explore its true inhibition potential. Assays of agar well diffusion performed with IDC (ultraviolet sterilized and pH adjusted 6.5) against isolated pure cultures of coliforms. The study protocol nullified effect of organic acids, volatile compounds, bacteriophages, and peroxides in IDC. Peptide nature of inhibitory ingredient was studied by Sodium Dodecyle Sulphate Polyacrylamide Gel Electrophoresis (SDS-PAGE), urea treatment. Computational phylogenetics revealed structural features of inhibitory ingredient. Statistical comparisons were done by analysis of variance. Second-order polynomial regression was done to evaluate the effect of IDC dilution on coliform inhibition. Mann–Whitney U-test performed to analyze different sample treatments.

Results:

Agar well diffusion (sealed bottom wells) shows inhibition of catalase-negative coliforms (confirmed by Gram staining and triple sugar iron agar assay) in pure culture (MacConkey agar). Activity diminished in urea, potentiated in ethylene diamine tetra acetic acid, remains unchanged by heat treatment (121°C, 15 min). SDS-PAGE revealed three distinct peptides (>10–15KDa). Hence, thermostable inhibitory peptides attached to target cell lead to observed activity (titer up to 1204.82 AU/ml with minimum 8 mm inhibition).

Conclusions:

IDC adequately inhibits sewage coliforms and may prevent dental plaques coliform colonization and its associated risks.

Prevalence of Vibrio cholerae in Coastal Alternative Supplies of Drinking Water and Association with Bacillus-Like Spore Formers

The scarcity of hygienic drinking water is a normal phenomenon in the coastal areas of Bangladesh due to the high salinity of ground water. The inhabitants of this locality, therefore, live on alternative supplies of water including rain-fed pond water, and rainwater with persistent complex microbial interactions therein, often contaminated with life-threatening pathogens. Hence, this study was aimed at analyzing the prevalence of Vibrio cholerae (Vc) in the alternative drinking waters of Mathbaria, a coastal subdistrict neighboring the Bay of Bengal, the efficacy of pond sand filter (PSF) and the co-association among Bacillus-like spore formers (Sf) and Vc. Vc presumably entrapped into the membrane filter was enriched in alkaline peptone water medium and was isolated on selective thiosulfate-citrate-bile salts-sucrose and taurocholate-tellurite-gelatin agar media. They were finally identified by immunochromatographic one step rapid test and serology test. A total of 26% Vc positive samples were obtained out of 100 [ponds—48, household (HH)—29, and PSFs—23] where 13% cases were pathogenic (Vc O1) and 13% were non-pathogenic (Vc non-O1/non-O139). The distribution of Vc as observed was 33, 26, and 13.8% in waters derived from pond surface, PSF, and HH reservoirs, respectively, and for pathogenic type, it was 62.5%, 50%, and nil, respectively. Although none of the samples was identified with pathogenic Vc O139, the statistics represents a significant and augmentative risk of cholera outbreak in the focused area. The antibiotic sensitivity pattern in this study resembled the trend observed during last few years for Vc. The PSF demonstrated its inability to remove Vc from any of the samples and in addition, the filter itself was evidenced to be the source of pathogens and spores in further contamination and transmission. The development of biofilm in the PSF could be hypothesized as the reservoir in contaminating pathogen-free water samples. From the test of homogeneity, the risk levels of alternative water sources were estimated equal regarding Vc. Simultaneously, it was determined statistically that the prevalence of Vc, by no means, is influenced by Bacillus-like Sf be it for pond surface, HH, or PSF derived water.

Antimicrobial activity of broccoli (Brassica oleracea var. italica) cultivar Avenger against pathogenic bacteria, phytopathogenic filamentous fungi and yeast

AIMS

The objective of this study was to show whether the edible part of broccoli has antibacterial and antifungal activity against micro-organism of importance in human health and vegetable spoilage, and to test if this effect was partially due to antimicrobial peptides (AMPs).

METHODS AND RESULTS

Crude extracts were obtained from florets and stems of broccoli cultivar Avenger and the inhibitory effect was demonstrated against pathogenic bacteria (Bacillus cereus, Staphylococcus xylosus, Staphylococcus aureus, Shigella flexneri, Shigella sonnei, Proteus vulgaris), phytopathogenic fungi (Colletotrichum gloeosporioides, Asperigillus niger) and yeasts (Candida albicans and Rhodotorula sp.). It was shown that samples treated with proteolytic enzymes had a reduction of approximately 60% in antibacterial activity against Staph. xylosus, suggesting that proteinaceous compounds might play a role in the inhibitory effect. Antimicrobial components in crude extracts were thermoresistant and the highest activity was observed under acidic conditions. It was shown that antifungal activity of broccoli's crude extracts might not be attributed to chitinases.

CONCLUSIONS

Organic broccoli cultivar Avenger has antimicrobial activity against pathogenic bacteria, yeast and phytophatogenic fungi. Data suggest that this effect is partially due to AMPs.

SIGNIFICANCE AND IMPACT OF THE STUDY

Broccoli's crude extracts have activity not only against pathogenic bacteria but also against phytophatogenic fungi of importance in agriculture. We suggest for first time that the inhibitory effect is probably due to AMPs.

Secondary metabolites from Bacillus amyloliquefaciens isolated from soil can kill Burkholderia pseudomallei

Bacillus species are Gram-positive bacteria found in abundance in nature and their secondary metabolites were found to possess various potential activities, notably antimicrobial. In this study, Bacillus amyloliquefaciens N2-4 and N3-8 were isolated from soil and their metabolites could kill Burkholderia pseudomallei, a Gram-negative pathogenic bacterium also found in soil in its endemic areas. Moreover, the metabolites were able to kill drug resistant isolates of B. pseudomallei and also inhibit other pathogenic bacteria such as Staphylococcus aureus, Escherichia coli and Acinetobacter baumannii but not the non-pathogenic Burkholderia thailandensis, which is closely related to B. pseudomallei. Since the antimicrobial activity of N3-8 was not partially decreased or abolished when treated with proteolytic enzymes or autoclaved, but N2-4 was, these two strains should have produced different compounds. The N3-8 metabolites with antimicrobial activity consisted of both protein and non-protein compounds. The inhibition spectrum of the precipitated proteins compared to the culture supernatant indicated a possible synergistic effect of the non-protein and peptide compounds of N3-8 isolates against other pathogens. When either N2-4 or N3-8 isolates was co-cultured with B. pseudomallei the numbers of the bacteria decreased by 5 log₁₀ within 72 h. Further purification and characterization of the metabolites is required for future use of the bacteria or their metabolites as biological controls of B. pseudomallei in the environment or for development as new drugs for problematic pathogenic bacteria.

Considerações sobre o tratamento das mastites

RESUMO: A mastite é considerada o maior problema dos animais destinados à produção de leite. Altera a sua composição e aumenta a contagem de células somáticas (CCS). Os micro-organismos envolvidos na doença podem ser origem infecciosa, como Staphylococcus aureus, ou ambiental, tal como Escherichia coli. A cultura bacteriana é uma ferramenta de diagnóstico e auxilia na detecção do patógeno causador da mastite. No entanto, fatores como fagocitose podem desencadear um resultado negativo. Quando estabelecido um programa de controle de mastite, o diagnóstico precoce e o início do tratamento adequado dos casos clínicos são fundamentais para se atingir os objetivos e seu sucesso, está relacionado com o patógeno envolvido. A indicação do tratamento de longa duração, ou terapia estendida, tem melhorado a resposta ao tratamento em casos de mastite por S. aureus, no entanto, com 30-50% de cura. Do ponto de vista do manejo dos animais, devido a alta contagiosidade deste patógeno, sua persistência no rebanho e custo em função ao tratamento, muitas vezes, o descarte do animal tem sido priorizado a fim de controlar os casos de mastite em propriedades. As medidas de controle são muito importantes para contribuir com a redução de casos de mastite por este patógeno. A indicação do tratamento intramamário associada com sistêmico tem poder efetivo em casos de mastite por E. coli, cujos casos agudos apresentam-se com sepse e toxemia. São abordados ainda aspectos de tratamentos alternativos das mastites, utilizados principalmente no processo orgânico de produção leiteira.

Bacillus thuringiensis: a successful insecticide with new environmental features and tidings

Bacillus thuringiensis (Bt) is known as the most successful microbial insecticide against different orders of insect pests in agriculture and medicine. Moreover, Bt toxin genes also have been efficiently used to enhance resistance to insect pests in genetically modified crops. In light of the scientific advantages of new molecular biology technologies, recently, some other new potentials of Bt have been explored. These new environmental features include the toxicity against nematodes, mites, and ticks, antagonistic effects against plant and animal pathogenic bacteria and fungi, plant growth-promoting activities (PGPR), bioremediation of different heavy metals and other pollutants, biosynthesis of metal nanoparticles, production of polyhydroxyalkanoate biopolymer, and anticancer activities (due to parasporins). This review comprehensively describes recent advances in the Bt whole-genome studies, the last updated known Bt toxins and their functions, and application of cry genes in plant genetic engineering. Moreover, the review thoroughly describes the new features of Bt which make it a suitable cell factory that might be used for production of different novel valuable bioproducts.

Purification and Characterization of a Novel Cold Shock Protein-Like Bacteriocin Synthesized by Bacillus thuringiensis

Bacillus thuringiensis (Bt), one of the most successful biopesticides, may expand its potential by producing bacteriocins (thuricins). The aim of this study was to investigate the antimicrobial potential of a novel Bt bacteriocin, thuricin BtCspB, produced by Bt BRC-ZYR2. The results showed that this bacteriocin has a high similarity with cold-shock protein B (CspB). BtCspB lost its activity after proteinase K treatment; however it was active at 60 °C for 30 min and was stable in the pH range 5-7. The partial loss of activity after the treatments of lipase II and catalase were likely due to the change in BtCspB structure and the partial degradation of BtCspB, respectively. The loss of activity at high temperatures and the activity variation at different pHs were not due to degradation or large conformational change. BtCspB did not inhibit four probiotics. It was only active against B. cereus strains 0938 and ATCC 10987 with MIC values of 3.125 μg/mL and 0.781 μg/mL, and MBC values of 12.5 μg/mL and 6.25 μg/mL, respectively. Taken together, these results provide new insights into a novel cold shock protein-like bacteriocin, BtCspB, which displayed promise for its use in food preservation and treatment of B. cereus-associated diseases.

Bacteriocins synthesized by Bacillus thuringiensis: generalities and potential applications

The members of the Bacillus thuringiensis group, commonly known as Bt, produce a huge number of metabolites, which show biocidal and antagonistic activity. B. thuringiensis is widely known for synthesizing Cry, Vip and Cyt proteins, active against insects and other parasporins with biocidal activity against certain types of cancerous cells. Nevertheless, B. thuringiensis also synthesizes compounds with antimicrobial activity, especially bacteriocins. Some B. thuringiensis bacteriocins resemble lantibiotics and other small linear peptides (class IIa) from the lactic acid bacteria bacteriocins classification system. Although many bacteriocins produced by Bt have been reported, there is no proper classification for them. In this work, we have grouped these based on molecular weight and functionality. Bacteriocins are small peptides synthesized by bacteria, presenting inhibitory activity against Gram-positive and Gram-negative bacteria and to a lesser extent against fungi. These molecules represent a good study model in the search for microbial control alternatives. Lactic acid bacteria produces a huge number of these types of molecules with great potential. Nonetheless, members of the Bacillus, cereus group, especially B. thuringiensis, emerge as an attractive alternative for obtaining bacteriocins showing novel activities. This review describes the potential applications of B. thuringiensis bacteriocins in the control of foodborne pathogens, environment and medical area.

Bacteriocinogenic Bacteria Isolated from Raw Goat Milk and Goat Cheese Produced in the Center of México

Currently, there are few reports on the isolation of microorganisms from goat milk and goat cheese that have antibacterial activity. In particular, there are no reports on the isolation of microorganisms with antibacterial activity from these products in central Mexico. Our objective was to isolate bacteria, from goat products, that synthesized antimicrobial peptides with activity against a variety of clinically significant bacteria. We isolated and identified Lactobacillus rhamnosus, L. plantarum, L. pentosus, L. helveticus and Enterococcus faecium from goat cheese, and Aquabacterium fontiphilum, Methylibium petroleiphilum, Piscinobacter aquaticus and Staphylococcus xylosus from goat milk. These bacteria isolated from goat cheese were able to inhibit Staphylococcus aureus, Bacillus cereus, Escherichia coli, Listeria monocytogenes, L. inoccua, Pseudomona aeruginosa, Shigella flexneri, Serratia marcescens, Enterobacter cloacae and Klebsiella pneumoniae. In addition, bacteria from goat milk showed inhibitory activity against B. cereus, L. lactis, E. coli, S. flexneri, E. cloacae and K. pneumonia; S. aureus, L. innocua, S. agalactiae and S. marcescens. The bacteriocins produced by these isolates were shown to be acid stable (pH 2-6) and thermotolerant (up to 100 °C), but were susceptible to proteinases. When screened by PCR for the presence of nisin, pediocin and enterocin A genes, none was found in isolates recovered from goat milk, and only the enterocin A gene was found in isolates from goat cheese.

Isolation and biochemical characterisation of a bacteriocin-like substance produced by Bacillus amyloliquefaciens An6

This study focuses on the isolation and characterisation of a peptide with bacteriocin-like properties from Bacillus amyloliquefaciens An6. Incubation conditions were optimised, and the effects of the incubation period and of carbon and nitrogen sources were investigated. The produced bacteriocin was partially purified with ammonium sulphate precipitation, dialysis and ultrafiltration and was then biochemically characterised. Maximum bacteriocin production was achieved after 48h of incubation in a culture medium containing 20g/L starch and 10g/L yeast extract, with an initial pH 8.0 at 30°C under continuous agitation at 200rpm. The bacteriocin was sequentially purified and its molecular weight was determined to be 11kDa by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The bacteriocin was relatively heat-resistant and was not sensitive to acid and alkaline conditions (pH 4.0-10.0). Its inhibitory activity was sensitive to proteinase K but was resistant to the proteolytic action of alcalase, trypsin, chymotrypsin and pepsin. In conclusion, bacteriocin An6, owing its wide spectrum of activity as well as its high tolerance to acidic and alkaline pH values, temperature and proteases shows great potential for use as a food biopreservative.

Diversity in the antibacterial potential of probiotic cultures Bacillus licheniformis MCC2514 and Bacillus licheniformis MCC2512

The aim of the present study was to investigate the characteristic diversity and stability of antimicrobial compounds produced by two probiotic strains of Bacillus licheniformis (MCC2514 and MCC2512). Antimicrobial compounds from the two strains notably varied, related to stability and potency. The inhibitory spectrum of B. licheniformis MCC2512 was higher than MCC2514, but, related to the effect on Micrococcus luteus ATCC9341, MCC2514 (LD50 = 450 AU ml(-1)) was more potent than MCC2512 (LD50 = 750 AU ml(-1)). The compounds were thermo-resistant and stable at a wide range of pH and exhibited considerable resistance to digestive enzymes and bile salts (anionic biological detergents), contributing to their appropriate application in various food systems. The isolate B. licheniformis MCC2512 gave a positive response to Bacillus subtilis-based biosensors BSF2470 and BS168.BS2, confirming the mode of action on the cell wall and subtilin-type, respectively. For B. licheniformis MCC2514, the mode of action was characterized by constructing B. subtilis reporters that interfered in five major biosynthetic pathways, i.e., biosynthesis of DNA, RNA, protein, the cell wall and fatty acids. B. licheniformis MCC2514 responded to the yvgS reporter, indicating it as an RNA synthesis inhibitor. Overall, the investigation reveals variability of the antimicrobial compounds from B. licheniformis of different origins and for their possible application as biopreservative agents.

Isolation and characterization of bacteriocinogenic lactic bacteria from M-Tuba and Tepache, two traditional fermented beverages in México

Mexican Tuba (M-Tuba) and Tepache are Mexican fermented beverages prepared mainly with pineapple pulp and coconut palm, respectively. At present, reports on the microbiota and nutritional effects of both beverages are lacking. The purpose of this study was to determine whether M-Tuba and Tepache contain cultivable lactic acid bacteria (LAB) capable of producing bacteriocins. Tepache and M-Tuba contain mesophilic aerobic bacteria, LAB, and yeast. Bacillus subtilis, Listeria monocytogenes, Listeria innocua, Streptococcus agalactiae, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Salmonella typhimurium, and Salmonella spp, were the microorganisms most susceptible to metabolites produced by bacterial isolates. M-Tuba and Tepache contain bacteria that harbor genes coding for nisin and enterocin, but not pediocin. The presence of Lactococcus lactis and E. faecium in M-Tuba and Tepache, was identified by 16S rDNA. These bacteria produced bacteriocins of ∼3.5 kDa and 4.0–4.5 kDa, respectively. Partial purified bacteriocins showed inhibitory effect against Micrococcus luteus, L. monocytogenes, L. innocua, Str. agalactiae, S. aureus, Bacillus cereus, B. subtilis, E. faecalis, and K. pneumoniae. We characterized, for the first time, cultivable microbiota of M-Tuba and Tepache, and specifically, identified candidate lactic bacteria (LAB) present in these beverages that were capable of synthesizing antimicrobial peptides, which collectively could provide food preservative functions.

Molecular detection and sensitivity to antibiotics and bacteriocins of pathogens isolated from bovine mastitis in family dairy herds of central Mexico

Thirty-two farms (n = 535 cows) located in the state of Guanajuato, Mexico, were sampled. Pathogens from bovine subclinical mastitis (SCM) and clinical mastitis (CLM) were identified by 16S rDNA and the sensitivity to both antibiotics and bacteriocins of Bacillus thuringiensis was tested. Forty-six milk samples were selected for their positive California Mastitis Test (CMT) (≥3) and any abnormality in the udder or milk. The frequency of SCM and CLM was 39.1% and 9.3%, respectively. Averages for test day milk yield (MY), lactation number (LN), herd size (HS), and number of days in milk (DM) were 20.6 kg, 2.8 lactations, 16.7 animals, and 164.1 days, respectively. MY was dependent on dairy herd (DH), LN, HS, and DM (P < 0.01), and correlations between udder quarters from the CMT were around 0.49 (P < 0.01). Coagulase-negative staphylococci were mainly identified, as well as Staphylococcus aureus, Streptococcus uberis, Brevibacterium stationis, B. conglomeratum, and Staphylococcus agnetis. Bacterial isolates were resistant to penicillin, clindamycin, ampicillin, and cefotaxime. Bacteriocins synthesized by Bacillus thuringiensis inhibited the growth of multiantibiotic resistance bacteria such as S. agnetis, S. equorum, Streptococcus uberis, Brevibacterium stationis, and Brachybacterium conglomeratum, but they were not active against S. sciuri, a microorganism that showed an 84% resistance to antibiotics tested in this study.

Bacteriocins from the rhizosphere microbiome - from an agriculture perspective

Bacteria produce and excrete a versatile and dynamic suit of compounds to defend against microbial competitors and mediate local population dynamics. These include a wide range of broad-spectrum non-ribosomally synthesized antibiotics, lytic enzymes, metabolic by-products, proteinaceous exotoxins, and ribosomally produced antimicrobial peptides (bacteriocins). Most bacteria produce at least one bacteriocin. Bacteriocins are of interest in the food industry as natural preservatives and in the probiotics industry, leading to extensive studies on lactic acid bacteria (colicin produced by Escherichia coli is a model bacteriocin). Recent studies have projected use of bacteriocins in veterinary medicine and in agriculture, as biostimulants of plant growth and development and as biocontrol agents. For example, bacteriocins such as Cerein 8A, Bac-GM17, putidacin, Bac 14B, amylocyclicin have been studied for their mechanisms of anti-microbial activity. Bac IH7 promotes tomato and musk melon plant growth. Thuricin 17 (Th17) is the only bacteriocin studied extensively for plant growth promotion, including at the molecular level. Th17 functions as a bacterial signal compound, promoting plant growth in legumes and non-legumes. In Arabidopsis thaliana and Glycine max Th17 increased phytohormones IAA and SA at 24 h post treatment. At the proteome level Th17 treatment of 3-week-old A. thaliana rosettes led to >2-fold changes in activation of the carbon and energy metabolism pathway proteins, 24 h post treatment. At 250 mM NaCl stress, the control plants under osmotic-shock shut down most of carbon-metabolism and activated energy-metabolism and antioxidant pathways. Th17 treated plants, at 250 mM NaCl, retained meaningful levels of the light harvesting complex, photosystems I and II proteins and energy and antioxidant pathways were activated, so that rosettes could better withstand the salt stress. In Glycine max, Th17 helped seeds germinate in the presence of NaCl stress, and was most effective at 100 mM NaCl. The 48 h post germination proteome suggested efficient and speedier partitioning of storage proteins, activation of carbon, nitrogen and energy metabolisms in Th17 treated seeds both under optimal and 100 mM NaCl. This review focuses on the bacteriocins produced by plant-rhizosphere colonizers and plant-pathogenic bacteria, that might have uses in agriculture, veterinary, and human medicine.

Bacteriocins ofBacillus thuringiensiscan expand the potential of this bacterium to other areas rather than limit its use only as microbial insecticide

Various strains of Bacillus thuringiensis are among the most successful entomopathogenic bacteria used commercially as biopesticides owing to their ability to synthesize insecticidal crystal (Cry) and cytolytic (Cyt) protein toxins during sporulation, and vegetative insecticidal (VIPs) proteins during the vegetative phase of growth. Whereas much is known about the molecular biology of Cry, Cyt, and VIPs, comparatively little is known about other proteins and metabolites synthesized by B. thuringiensis that could also have applied value. Here, we review recent reports on bacteriocins synthesized by this bacterium as they relate to antibacterial activity, molecular genetics, biophysical and biochemical properties, and methods used to separate and purify these antimicrobial peptides. We highlight the potential of bacteriocins for use as food preservatives, antibiotics, plant protection, and plant growth promoters. We suggest that B. thuringiensis could be used not only in biological control of insects but also in other agronomical and industrial areas of public interest.

Expanding the use of a fluorogenic method to determine activity and mode of action of Bacillus thuringiensis bacteriocins against Gram-positive and Gram-negative bacteria

Previously we described a rapid fluorogenic method to measure the activity of five bacteriocins produced by Mexican strains of Bacillus thuringiensis against B. cereus 183. Here we standardize this method to efficiently determine the activity of bacteriocins against both Gram-positive and Gram-negative bacteria. It was determined that the crucial parameter required to obtain reproducible results was the number of cells used in the assay, that is, ~4 × 10⁸ cell/mL and ~7 × 10⁸ cell/mL, respectively, for target Gram-positive and Gram-negative bacteria. Comparative analyses of the fluorogenic and traditional well-diffusion assays showed correlation coefficients of 0.88 to 0.99 and 0.83 to 0.99, respectively, for Gram-positive and Gram-negative bacteria. The fluorogenic method demonstrated that the five bacteriocins of B. thuringiensis have bacteriolytic and bacteriostatic activities against all microorganisms tested, including clinically significant bacteria such as Listeria monocytogenes, Proteus vulgaris, and Shigella flexneri reported previously to be resistant to the antimicrobials as determined using the well-diffusion protocol. These results demonstrate that the fluorogenic assay is a more sensitive, reliable, and rapid method when compared with the well-diffusion method and can easily be adapted in screening protocols for bacteriocin production by other microorganisms.

Isolation of a new Mexican strain of Bacillus subtilis with antifungal and antibacterial activities

Although several strains of B. subtilis with antifungal activity have been isolated worldwide, to date there are no published reports regarding the isolation of a native B. subtilis strain from strawberry plants in Mexico. A native bacterium (Bacillus subtilis 21) demonstrated in vitro antagonistic activity against different plant pathogenic fungi. Under greenhouse conditions, it was shown that plants infected with Rhizoctonia solani and Fusarium verticillioides and treated with B. subtilis 21 produced augment in the number of leaves per plant and an increment in the length of healthy leaves in comparison with untreated plants. In addition, B. subtilis 21 showed activity against pathogenic bacteria. Secreted proteins by B. subtilis 21 were studied, detecting the presence of proteases and bacteriocin-like inhibitor substances that could be implicated in its antagonistic activity. Chitinases and zwittermicin production could not be detected. Then, B. subtilis 21 could potentially be used to control phytopathogenic fungi that infect strawberry plants.

Effects of physical culture parameters on bacteriocin production by Mexican strains of Bacillus thuringiensis after cellular induction

We have shown previously that in the presence of inducer Bacillus cereus 183, significant increases in bacteriocin production and bactericidal activity of B. thuringiensis occur when the latter is cultivated at pH 7.2, 28°C, and 180 rpm. Here we show that this activity can be further improved when B. thuringiensis is induced with B. cereus 183 and then cultivated with modification of pH, temperature, and agitation. Five native strains of B. thuringiensis, LBIT 269, LBIT 287, LBIT 404, LBIT 420, and LBIT 524 which synthesize, respectively, morricin 269, kurstacin 287, kenyacin 404, entomocin 420, and tolworthcin 524, were cultivated in four different fermentation media. Of these, fermentation in tryptic soy broth (TSB) yielded the highest level of bacteriocin activity (~100–133 FU). Bacteria grown in TSB were induced with B. cereus 183 and cultivated at different pH (6.0, 7.2, 8.0), temperature (26, 28, 30°C), and agitation (150, 180, 210 rpm). Full factorial design was performed and results were analyzed with analysis of variance (ANOVA) and Tukey multiple comparison tests at significant level of α ≤ 0.05 to study the influence of the three variables on bacterial growth and bacteriocin production. Our data show that the highest bacteriocin activity was found with LBIT 269 and LBIT 404 with an increase of ~95–100% compared with induced B. thuringiensis strains cultivated under fixed conditions (pH 7.2, 28°C, 180 rpm), for which the data were set at 0%. The optimal conditions for morricin 269 and kenyacin 404 production were, respectively, pH 8, 30°C, 210 rpm and pH 7.2, 26°C, 210 rpm.

Antimicrobial factor from Bacillus amyloliquefaciens inhibits Paenibacillus larvae, the causative agent of American foulbrood

Bacillus amyloliquefaciens LBM 5006 produces an antimicrobial factor active against Paenibacillus larvae, a major honeybee pathogen. The antagonistic effect and the mode of action of the antimicrobial factor were investigated. The antibacterial activity was produced starting at mid-logarithmic growth phase, reaching its maximum during the stationary phase. Exposure of cell suspensions of P. larvae to this antimicrobial resulted in loss of cell viability and reduction in optical density associated with cell lysis. Scanning electron microscopy showed damaged cell envelope and loss of protoplasmic material. The antimicrobial factor was stable for up to 80°C, but it was sensitive to proteinase K and trypsin. Mass spectrometry analysis indicates that the antimicrobial activity is associated with iturin-like peptides. The antimicrobial factor from B. amyloliquefaciens LBM 5006 showed a bactericidal effect against P. larvae cells and spores. This is the first report on iturin activity against P. larvae. This antimicrobial presents potential for use in the control of American foulbrood disease.

Diversity and applications of Bacillus bacteriocins

Members of the genus Bacillus are known to produce a wide arsenal of antimicrobial substances, including peptide and lipopeptide antibiotics, and bacteriocins. Many of the Bacillus bacteriocins belong to the lantibiotics, a category of post-translationally modified peptides widely disseminated among different bacterial clades. Lantibiotics are among the best-characterized antimicrobial peptides at the levels of peptide structure, genetic determinants and biosynthesis mechanisms. Members of the genus Bacillus also produce many other nonmodified bacteriocins, some of which resemble the pediocin-like bacteriocins of the lactic acid bacteria (LAB), while others show completely novel peptide sequences. Bacillus bacteriocins are increasingly becoming more important due to their sometimes broader spectra of inhibition (as compared with most LAB bacteriocins), which may include Gram-negative bacteria, yeasts or fungi, in addition to Gram-positive species, some of which are known to be pathogenic to humans and/or animals. The present review provides a general overview of Bacillus bacteriocins, including primary structure, biochemical and genetic characterization, classification and potential applications in food preservation as natural preservatives and in human and animal health as alternatives to conventional antibiotics. Furthermore, it addresses their environmental applications, such as bioprotection against the pre- and post-harvest decay of vegetables, or as plant growth promoters.

Isolation of Salmonella spp. from lettuce and evaluation of its susceptibility to novel bacteriocins of Bacillus thuringiensis and antibiotics

In this study, 13% of fresh lettuce (Lactuca sativa) samples collected from markets and supermarkets in two cities of Mexico were contaminated with Salmonella spp. From those samples, amplicons of ∼300 base pairs (bp) were amplified, corresponding to the expected size of the invasion (invA) and internal transcribed spacer regions of the 16S and 23S rRNA genes of Salmonella spp. Additionally, Salmonella strains were isolated and harbored plasmids ranging from ∼9 to 16 kbp. From these strains, 91% were resistant to ampicillin and nitrofurantoin, whereas 55% were resistant to cephalothin and chloramphenicol. No resistance was detected to amikacin, carbenicillin, cefotaxime, gentamicin, netilmicin, norfloxacin, and sulfamethoxazole-trimethoprim. When Salmonella isolates were tested against novel bacteriocins (morricin 269, kurstacin 287, kenyacin 404, entomocin 420, and tolworthcin 524) produced by five Mexican strains of Bacillus thuringiensis, 50% were susceptible to these antimicrobial peptides. This is the first report showing that Salmonella strains isolated from lettuce are susceptible to bacteriocins produced by the most important bioinsecticide worldwide, suggesting the potential use of these antibacterial peptides as therapeutic agents or food preservatives to reduce or destroy populations of Salmonella spp.

Generation of chitin-derived oligosaccharides toxic to pathogenic bacteria using ChiA74, an endochitinase native to Bacillus thuringiensis

AIMS

To demonstrate that an endochitinase (ChiA74) native to Bacillus thuringiensis can be used to generate chitin-derived oligosaccharides (OGS) with antibacterial activity against a number of aetiological agents of disease, including bacteria that cause diarrhoeal and emetic syndromes in humans.

METHODS AND RESULTS

The intact chiA74 with its cis elements was cloned into high and moderately high copy number Escherichia coli expression vectors. Functionally secreted ChiA74 was produced, and the endochitinase cleaved substrate colloidal chitin to produce OGS with 3, 5 and 6 degrees of polymerization. The enzyme was active for an extended period of incubation (24 h), but its activity showed a decrement of 73% and 87%, respectively, after 24 h of incubation at 37 and 55 degrees C. OGS showed inhibitory activity against Bacillus cereus, Listeria inoccua, E. coli, Staphylococcus xylosus, Salmonella species, Staphylococcus aureus, Pseudomona aeruginosa, Shigella flexneri, and Proteus vulgaris.

CONCLUSIONS

Endochitinase ChiA74 is able to stably maintain hydrolytic activity during prolonged incubation in a mix reaction with chitin to produce bioactive OGS with inhibitory activity against important food-borne pathogenic bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study showing that an endochitinase (ChiA74) native of the most important bioinsecticide used worldwide (B. thuringiensis), but here produced in E. coli, is able to generate chitin-derived OGS with antibacterial activity against clinically significant food-borne pathogenic bacteria.

Generation of antibacterial oligosaccharides derived from chitin using heterologous endochitinase synthesized in Escherichia coli

AIMS

To synthesize two heterologous endochitinases in Escherichia coli and demonstrate their potential for applied use in generating antibacterial chitin-derived oligosaccharides (OGS).

METHODS AND RESULTS

Heterologous endochitinase genes, chiA Nima and chiA74, were expressed in E. coli. Endochitinases were secreted by the E. coli export machinery and by approximately 20 h maximal chitinolytic activity was observed. The highest chitinolytic activity was observed with ChiA Nima, which produced antibacterial OGS with activities against Enterobacter cloacae, Escherichia coli, Staphylococcus aureus and S. xylosus.

CONCLUSIONS

It was shown that the export machinery of E. coli is well suited for the secretion of bioactive ChiA74 and ChiA Nima endochitinases, and that the latter can generate antibacterial OGS.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our study suggests that it is feasible to synthesize endochitinases ChiA Nima and ChiA74 codified by E. coli and mass-produce these enzymes in culture supernatants. As signal peptides in native ChiA Nima and ChiA74 were recognized by the protein export molecular apparatus in E. coli, these short peptides could be included as signal sequences for transport in E. coli of other proteins with applied value. This is the first report suggesting that ChiA Nima can be used to produce OGS to control food-borne pathogenic bacteria.

Gut bacteria are not required for the insecticidal activity of Bacillus thuringiensis toward the tobacco hornworm, Manduca sexta

It was recently proposed that gut bacteria are required for the insecticidal activity of the Bacillus thuringiensis-based insecticide, DiPel, toward the lepidopterans Manduca sexta, Pieris rapae, Vanessa cardui, and Lymantria dispar. Using a similar methodology, it was found that gut bacteria were not required for the toxicity of DiPel or Cry1Ac or for the synergism of an otherwise sublethal concentration of Cry1Ac toward M. sexta. The toxicities of DiPel and of B. thuringiensis HD73 Cry(-) spore/Cry1Ac synergism were attenuated by continuously exposing larvae to antibiotics before bioassays. Attenuation could be eliminated by exposing larvae to antibiotics only during the first instar without altering larval sterility. Prior antibiotic exposure did not attenuate Cry1Ac toxicity. The presence of enterococci in larval guts slowed mortality resulting from DiPel exposure and halved Cry1Ac toxicity but had little effect on B. thuringiensis HD73 Cry(-) spore/Cry1Ac synergism. B. thuringiensis Cry(-) cells killed larvae after intrahemocoelic inoculation of M. sexta, Galleria mellonella, and Spodoptera litura and grew rapidly in plasma from M. sexta, S. litura, and Tenebrio molitor. These findings suggest that gut bacteria are not required for B. thuringiensis insecticidal activity toward M. sexta but that B. thuringiensis lethality is reduced in larvae that are continuously exposed to antibiotics before bioassay.

Activity of bacteriocins synthesized by Bacillus thuringiensis against Staphylococcus aureus isolates associated to bovine mastitis

Antimicrobial therapy is a useful tool to control bovine mastitis caused by Staphylococcus aureus, as consequence an increase in staphylococci resistant cases has been registered. Alternative strategies are desirable and bacteriocins represent attractive control agents to prevent bovine mastitis. The aim of this work was to evaluate the activity of five bacteriocins synthesized by Bacillus thuringiensis against S. aureus isolates associated to bovine mastitis. Fifty S. aureus isolates were recovered from milk composite samples of 26 Holstein lactating cows from one herd during September 2007 to February 2008 in México and susceptibility of those isolates to 12 antibiotics and 5 bacteriocins from B. thuringiensis was evaluated. S. aureus isolates were mainly resistant to penicillin (92%), dicloxacillin (86%), ampicillin (74%) and erythromycin (74%); whereas susceptibility to gentamicin, trimethoprim and tetracycline was detected at, respectively, 92%, 88%, and 72%. All S. aureus isolates showed susceptibility to the five bacteriocins synthesized by B. thuringiensis, mainly to morricin 269 and kurstacin 287 followed by kenyacin 404, entomocin 420 and tolworthcin 524. Our results showed that S. aureus isolates had differences in the antimicrobial resistance patterns and were susceptible to bacteriocins produced by B. thuringiensis, which could be useful as an alternative method to control bovine mastitis.