Vibriostatic effects of probiotic Bacillus licheniformis Dahb1 and its molecular phylogeny resolved through RAPD markers

Protective effects of dietary supplementation of probiotic Bacillus licheniformis Dahb1 against ammonia induced immunotoxicity and oxidative stress in Oreochromis mossambicus

The goal of this study was to assess the efficacy of probiotics in mitigating ammonia-induced toxicity in fish. Fish were divided into four groups: control, only probiotic, only ammonia, and combined ammonia + probiotic. For 8 weeks, the Oreochromis mossambicus were exposed to waterborne ammonia at 1.0 mg L^-1 and/or dietary Bacillus licheniformis Dahb1 at 10⁷ cfu g^-1. After the 4^th and 8^th weeks, the fish were evaluated for growth performance, enzymatic and non-enzymatic antioxidant activities (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) reduced glutathione (GSH), neurotoxicity (acetylcholinesterase - AChE), non-specific immune responses (lysozyme (LYZ), myeloperoxidase (MPO), reactive nitrogen and oxygen species (RNS and ROS) and oxidative stress effects (lipid peroxidation (LPO), DNA damage)). Our results showed that in the absence of waterborne ammonia exposure, B. licheniformis Dahb1 significantly improved growth performance, enzymatic and non-enzymatic antioxidant capacity, AChE activity, non-specific immune response and decreased oxidative stress effect. Ammonia exposure resulted in significantly lower growth performance, reduced enzymatic and non-enzymatic antioxidant ability, decreased AChE activity, decreased non-specific immune response and increased oxidative stress effect. When O. mossambicus were exposed to ammonia, supplementation with B. licheniformis Dahb1 in the diet significantly increased survival, indicating that it may have a significant protective effect against ammonia toxicity by enhancing enzymatic and non-enzymatic antioxidant ability, activity of AChE, non-specific immune response and reduced oxidative stress effect. According to our findings, diet supplementation of B. licheniformis Dahb1 (10⁷ cfu g^-1) has the potential to combat ammonia toxicity in O. mossambicus.

Structural characterization of Bacillus licheniformis Dahb1 exopolysaccharide-antimicrobial potential and larvicidal activity on malaria and Zika virus mosquito vectors

Microbial polysaccharides produced by marine species play a key role in food and cosmetic industry, as they are nontoxic and biodegradable polymers. This investigation reports the isolation of exopolysaccharide from Bacillus licheniformis Dahb1 and its biomedical applications. Bacillus licheniformis Dahb1 exopolysaccharide (Bl-EPS) was extracted using the ethanol precipitation method and structurally characterized. FTIR and ¹H-NMR pointed out the presence of various functional groups and primary aromatic compounds, respectively. Bl-EPS exhibited strong antioxidant potential confirmed via DPPH radical, reducing power and superoxide anion scavenging assays. Microscopic analysis revealed that the antibiofilm activity of Bl-EPS (75 μg/ml) was higher against Gram-negative (Pseudomonas aeruginosa and Proteus vulgaris) bacteria over Gram-positive species (Bacillus subtilis and Bacillus pumilus). Bl-EPS led to biofilm inhibition against Candida albicans when tested at 75 μg/ml. The hemolytic assay showed low cytotoxicity of Bl-EPS at 5 mg/ml. Besides, Bl-EPS achieved LC₅₀ values < 80 μg/ml against larvae of mosquito vectors Anopheles stephensi and Aedes aegypti. Overall, our findings pointed out the multipurpose bioactivity of Bl-EPS, which deserves further consideration for pharmaceutical, environmental and entomological applications.

Dietary supplementation of probiotic Bacillus licheniformis Dahb1 improves growth performance, mucus and serum immune parameters, antioxidant enzyme activity as well as resistance against Aeromonas hydrophila in tilapia Oreochromis mossambicus

The present study evaluated the dietary supplementation of probiotic Bacillus licheniformis Dahb1 on the growth performance, immune parameters and antioxidant enzymes activities in serum and mucus as well as resistance against Aeromonas hydrophila in Mozambique tilapia Oreochromis mossambicus. Fish (24 ± 2.5 g) were fed separately with three diets, 1) commercial diet (control), 2) diet containing probiotic at 10⁵ cfu g^-1 (D1) and 3) diet containing probiotic at 10⁷ cfu g^-1 (D2) for 4 weeks. Growth performance in term of final weight (FW) specific growth rate (SGR) and feed conversion ratio (FCR), immune parameters of total protein (TP), alkaline phosphatase (ALP), myeloperoxidase (MPO), lysozyme (LYZ), reactive oxygen species (ROS), reactive nitrogen species (RNS) and antioxidant parameters of superoxide dismutase (SOD) and glutathione peroxidase (GPx) in serum and mucus were evaluated after 2^nd and 4^th weeks. The FW, SGR, and FCR of fish fed with D1 and D2 significantly improved (p < 0.05). The activities of ALP, LYZ and MPO in the mucus were significantly higher (p < 0.05) in fish that fed D1 and D2. The TP, ROS, RNS, SOD and GPx in the serum were significantly higher (p < 0.05) in fish that fed D1 and D2. In addition, the challenge test showed that fish fed D1 and D2 enhanced significantly (p < 0.05) the resistance against A. hydrophila (1 × 10⁷ cells ml^-1). In conclusion, probiotic B. licheniformis Dahb1 can be applied in diet at 10⁷ cfu g^-1 to improve healthy status and resistance against A. hydrophila in tilapia farming.

Bacterial exopolysaccharide (EPS)-coated ZnO nanoparticles showed high antibiofilm activity and larvicidal toxicity against malaria and Zika virus vectors

In this study, a novel and effective approach was performed to synthesize ZnO nanoparticles (ZnO NPs) using the exopolysaccharides (EPS) from the probiotic strain Bacillus licheniformis Dahb1. EPS acted as reducing and stabilizing agent for the formation of EPS-ZnO NPs by co-precipitation method. Structural characterization was investigated by a surface plasma resonance centered at 375nm in UV-vis spectrum. FTIR spectrum exhibited functional groups with strong absorption peak at 3814.7-420cm^-1. XRD showed the crystalline nature of EPS-ZnO NPs. TEM showed that the EPS-ZnO NPs were hexagonal in shape, with size within the range of 10-100nm. The presence of Zn was confirmed by EDX analysis. Antibacterial activity of EPS-ZnO NPs was demonstrated as 100μg/ml significantly inhibited the effective growth control of Gram-negative (Pseudomonas aeruginosa and Proteus vulgaris) and Gram-positive (Bacillus subtilis and Bacillus pumilus) bacteria. Light microscopy and confocal laser scanning microscopy evidenced that the antibiofilm activity of EPS-ZnO NPs was higher against Gram-negative bacteria over Gram positive bacteria. EPS-ZnO NPs also inhibited the biofilm growth of Candida albicans at the concentration of 75μg/ml. The hemolytic test showed low cytotoxicity of EPS-ZnO NPs at 5mg/ml. In addition, EPS-ZnO NPs achieved 100% mortality against third instars mosquito larvae of Anopheles stephensi and Aedes aegypti at very low doses. Moreover, histology studies revealed the presence of damaged cells and tissues in the mid-gut of treated mosquito larvae. The multipurpose properties of EPS-ZnO NPs revealed in the present study can be further considered for pharmaceutical, parasitological and entomological applications.

In vitro antagonistic activity and the protective effect of probiotic Bacillus licheniformis Dahb1 in zebrafish challenged with GFP tagged Vibrio parahaemolyticus Dahv2

In vitro antagonistic activity and the protective effect of probiotic Bacillus licheniformis Dahb1 in zebrafish (Danio rerio) challenged with GFP tagged Vibrio parahaemolyticus Dahv2 was studied. The cell free extract of probiotic B. licheniformis Dahb1 at 100 μg mL^-1 showed growth inhibition of V. parahaemolyticus Dahv2 in vitro. B. licheniformis Dahb1 also inhibited the biofilm growth of GFP tagged V. parahaemolyticus Dahv2 at 100 μg mL^-1 in vitro. The growth and survival of zebrafish was tested using probiotic B. licheniformis Dahb1. Weight (1.28 g) of zebrafish that received the cell free extract was much higher than in control (1.04 g). The mortality of zebrafish infected with GFP tagged V. parahaemolyticus Dahv2 at 10⁷ Cfu mL^-1 (Group IV) was 100%, whereas a complete survival of zebrafish that received the cell free extract of B. licheniformis Dahb1 at 10⁷ Cfu mL^-1 (Group VII) was observed after 30 days. The number of GFP tagged V. parahaemolyticus Dahv2 colonies in the intestine and gills significantly reduced after treatment with the cell free extract of B. licheniformis Dahb1. Furthermore, a significant decrease in the fluorescent colonies of GFP tagged V. parahaemolyticus Dahv2 was observed after treatment with the cell free extract of B. licheniformis Dahb1 under confocal laser scanning microscopy (CLSM). In conclusion, the cell free extract of B. licheniformis Dahb1 could prevent Vibrio infection by enhancing the growth and survival of zebrafish.

GFP tagged Vibrio parahaemolyticus Dahv2 infection and the protective effects of the probiotic Bacillus licheniformis Dahb1 on the growth, immune and antioxidant responses in Pangasius hypophthalmus

In this study, the pathogenicity of GFP tagged Vibrio parahaemolyticus Dahv2 and the protective effect of the probiotic strain, Bacillus licheniformis Dahb1 was studied on the Asian catfish, Pangasius hypophthalmus. The experiment was carried out for 24 days with three groups and one group served as the control (without treatment). In the first group, P. hypophthalmus was orally infected with 1 mL of GFP tagged V. parahaemolyticus Dahv2 at two different doses (10(5) and 10(7) cfu mL(-1)). In the second group, P. hypophthalmus was orally administrated with 1 ml of the probiotic B. licheniformis Dahb1 at two different doses (10(5) and 10(7) cfu mL(-1)). In the third group, P. hypophthalmus was orally infected first with 1 mL of GFP tagged V. parahaemolyticus Dahv2 followed by the administration of 1 mL of B. licheniformis Dahb1 (combined treatment) at two different doses (10(5) and 10(7) cfu mL(-1)). The growth, immune (myeloperoxidase, respiratory burst, natural complement haemolytic and lysozyme activity) and antioxidant (glutathione-S-transferase, reduced glutathione and total glutathione) responses of P. hypophthalmus were reduced after post infection of GFP tagged V. parahaemolyticus Dahv2 compared to control. However, after administration with the probiotic B. licheniformis Dahb1 at 10(5) cfu mL(-1), P. hypophthalmus showed significant increase in the growth, immune and antioxidant responses compared to 10(7) cfu mL(-1). On the otherhand, the growth, immune and antioxidant responses of P. hypophthalmus infected and administrated with combined GFP tagged Vibrio + Bacillus at 10(5) cfu mL(-1) were relatively higher than that of GFP tagged V. parahaemolyticus Dahv2 and control groups but lower than that of probiotic B. licheniformis Dahb1 groups. The results of the present study conclude that the probiotic B. licheniformis Dahb1 at 10(5) cfu mL(-1) has the potential to protect the P. hypophthalmus against V. parahaemolyticus Dahv2 infection by enhancing the growth, immune and antioxidant responses. The probiotic B. licheniformis Dahb1 would be effectively used in the treatment of aquatic diseases for improvement of aquaculture industry.

Essential oils of Nigella sativa protects Artemia from the pathogenic effect of Vibrio parahaemolyticus Dahv2

The anti-Vibrio activity of essential oils (EOs) of nine medicinal plants was tested against 28 Vibrio spp. isolated from diseased Fenneropenaeus indicus. EO of Nigella sativa exhibited anti-Vibrio activity against all Vibrio spp. and greater inhibition was noted for the isolate V2 which was identified as Vibrio parahaemolyticus Dahv2. Further, EO of N. sativa effectively inhibited V. parahaemolyticus Dahv2 with an inhibition zone of 23.9mm at 101.2μgml(-1). Moreover, EO of N. sativa revealed anti-biofilm activity at 101.2μgml(-1) against V. parahaemolyticus Dahv2 and inhibited the growth of V. parahaemolyticus Dahv2 at 100μgml(-1).In vivo experimental infection studies showed that the survival of Artemia spp. infected with V. parahaemolyticus Dahv2 at 1×10(3)cfuml(-1) was only 40%. However, the survival of Artemia spp. was significantly increased after challenge with 100μgml(-1) of EO of N. sativa. EO of N. sativa showed higher anti-oxidant potential and total phenol content than other EOs tested. The anti-oxidant activity of EO of N. sativa was highly correlated to their total phenolic contents (r=0.836, P<0.05). This observation suggests that EO of N. sativa protected the Artemia spp. after experimental infection of V. parahaemolyticus Dahv2.

Biosynthesis of silver nanoparticles using a probiotic Bacillus licheniformis Dahb1 and their antibiofilm activity and toxicity effects in Ceriodaphnia cornuta

In the present study, we synthesized and characterized a probiotic Bacillus licheniformis cell free extract (BLCFE) coated silver nanoparticles (BLCFE-AgNPs). These BLCFE-AgNPs were characterized by UV-visible spectrophotometer, XRD, EDX, FTIR, TEM and AFM. A strong surface plasmon resonance centered at 422 nm in UV-visible spectrum indicates the formation of AgNPs. The XRD spectrum of silver nanoparticles exhibited 2θ values corresponding to the silver nanocrystal. TEM and AFM showed the AgNPs were spherical in shape within the range of 18.69-63.42 nm and the presence of silver was confirmed by EDX analysis. Light and Confocal Laser Scanning Microscope (CLSM) images showed a weak adherence and disintegrated biofilm formation of Vibrio parahaemolyticus Dav1 treated with BLCFE-AgNPs compared to control. This result suggests that BLCFE-AgNps may be used for the control of biofilm forming bacterial populations in the biomedical field. In addition, acute toxicity results concluded that BLCFE-AgNPs were less toxic to the fresh water crustacean Ceriodaphnia cornuta (50 μg/ml) when compared to AgNO3 (22 μg/ml). This study also reports a short term analysis (24 h) of uptake and depuration of BLCFE-AgNPs in C. cornuta.