Preliminary study on high-level expression of tandem-arranged tachyplesin-encoding gene in Bacillus subtilis Wb800 and its antibacterial activity

Antimicrobial Resistance and Recent Alternatives to Antibiotics for the Control of Bacterial Pathogens with an Emphasis on Foodborne Pathogens

Antimicrobial resistance (AMR) is one of the most important global public health problems. The imprudent use of antibiotics in humans and animals has resulted in the emergence of antibiotic-resistant bacteria. The dissemination of these strains and their resistant determinants could endanger antibiotic efficacy. Therefore, there is an urgent need to identify and develop novel strategies to combat antibiotic resistance. This review provides insights into the evolution and the mechanisms of AMR. Additionally, it discusses alternative approaches that might be used to control AMR, including probiotics, prebiotics, antimicrobial peptides, small molecules, organic acids, essential oils, bacteriophage, fecal transplants, and nanoparticles.

Characteristics of tylosin and enrofloxacin degradation in swine manure digested by black soldier fly (Hermetia illucens L.) larvae

Black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae) larvae (BSF larvae or BSFL) offer an environmental-friendly method for degrading antibiotics, such as tylosin (TYL) and enrofloxacin (EF), in swine manure. This study examined the impact of temperature on this process, role of associated microbes, dynamics of resistant genes, and a description of the microbial community associated with the BSF larval gut, how microbes isolated from the BSF larval gut as inoculants impact the process as well as enhance antibiotic digestion, and finally a quantification of antibiotics in BSF larvae fed manure with TYL or EF. Antibiotic degradation in manure was optimized at 28 °C with at least 10% greater than 23 °C and 37 °C. More than 40% reduction in TYL and EF concentrations in the manure occurred when BSF larval gut associated microbes were present. Furthermore, DNA extracted from the gut of non-sterile BSF larvae fed manure with TYL or EF indicated at least two 2^-△△Ct fold increase in antibiotic resistance genes for TYL and EF. We identified 250, 4, and 16 unique operational taxa for larvae fed control manure and manure with either TYL or EF. Intestinal microbes isolated from non-sterile larvae fed manure with TYL or EF, were identified, cultured, and examined for their ability to degrade TYL and EF in Luria-Bertani (LB) medium. Three strains (two strains of Enterococcus faecalis and one strain of Proteus mirabilis) resulted in at least 50% TYL or EF degradation within 96 h. Sterile BSF larvae inoculated with P. mirabilis recovered >60% of the degradation ability exhibited by non-sterile larvae. Finally, no TYL residuals were found in 14-d-old larvae, prepupae, or pupae of BSF immatures fed manure containing these antibiotics. While ∼65 μg/g and ∼20 μg/g of EF were found in larval contents and pupal exoskeleton, respectively.

Expression of recombinant tachyplesin I in Pichia pastoris

The development of antibiotic-resistant bacteria has become a major public health problem, prompting the search for alternative solutions. Tachyplesin I (TP-I) is an antimicrobial peptide, which exhibits potent and broad-spectrum activities against bacteria, fungi, viruses, and tumor cells. However, limited amounts of TP-I produced in horseshoe crab restrict its large-scale use. In order to solve this problem, a eukaryotic expression system of Pichia pastoris with high TP-I expression was constructed by gene engineering. To achieve high expression of TP-I, 74 amino acid-long peptide (4TP-1) was designed containing 4 copies of TP-I, and specific cleavage sites for pancreatic elastase (-Ala↓ or -Gly↓) and carboxypeptidase A (cleaves C terminal amino acid); these cleavage sites for enzymes were located between the four copies of TP-I. The gene sequence for the designed peptide was synthesized taking into consideration codon preferences for P. pastoris, and cloned into the highly efficient expression vector pGAPZα B. Host Pichia pastoris strain GS115 cells were transfected by the constructed expression vector pGAPZα B-4tp-I by electroporation. Tricine-SDS-PAGE electrophoresis was carried out to detect the expression of target peptides in the fermentation medium. This analysis showed a protein band of 3.3 kDa, identical to that of chemically synthesized TP-I, verifying that successful synthesis and secretion of TP-I by genetically engineered P. pastoris. The concentration of TP-I in the fermentation broth was 27.24-29.53 mg/L. High-resolution mass spectrometry analysis documented that the TP-I monomer had the same molecular weight, 2262.85, as the designed 17-amino acid sequence. The recombinant TP-I peptide displayed different levels of bactericidal activity against Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa, and Staphylococcus aureus. Thus, the present study demonstrated the feasibility of achieving high levels of expression of TP-I in P. pastoris.

Anti-infective biomaterials with surface-decorated tachyplesin I

Implants decorated with antimicrobial peptides (AMPs) can prevent infection and reduce the risk of creating antibiotic resistance. Yet the restricted mobility of surficial AMP often compromises its activity. Here, we report a simple but effective strategy to allow a more flexible display of AMP on the biomaterial surface and demonstrate its efficacy for wound healing. The AMP, tachyplesin I (Tac), is tagged with the polyhydroxyalkanoate-granule-associated protein (PhaP) and immobilized on haloarchaea-produced poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) via hydrophobic interaction. The PhaP-Tac coating effectively inhibits the growth of both Gram-negative and Gram-positive bacteria. It also increases the surface hydrophilicity to improve fibroblast proliferation in vitro, and accelerates wound healing by decreasing bacterial counts to below 10⁵ CFU per gram of tissue in a deep-wound mouse model in vivo. Taken together, these findings demonstrate an effective strategy to realize the full potential of AMPs in imparting implants with an anti-microbial activity that is localized and potent.

Experimental Induction of Bacterial Resistance to the Antimicrobial Peptide Tachyplesin I and Investigation of the Resistance Mechanisms

Tachyplesin I is a 17-amino-acid cationic antimicrobial peptide (AMP) with a typical cyclic antiparallel β-sheet structure that is a promising therapeutic for infections, tumors, and viruses. To date, no bacterial resistance to tachyplesin I has been reported. To explore the safety of tachyplesin I as an antibacterial drug for wide clinical application, we experimentally induced bacterial resistance to tachyplesin I by using two selection procedures and studied the preliminary resistance mechanisms. Aeromonas hydrophila XS91-4-1, Pseudomonas aeruginosa CGMCC1.2620, and Escherichia coli ATCC 25922 and F41 showed resistance to tachyplesin I under long-term selection pressure with continuously increasing concentrations of tachyplesin I. In addition, P. aeruginosa and E. coli exhibited resistance to tachyplesin I under UV mutagenesis selection conditions. Cell growth and colony morphology were slightly different between control strains and strains with induced resistance. Cross-resistance to tachyplesin I and antimicrobial agents (cefoperazone and amikacin) or other AMPs (pexiganan, tachyplesin III, and polyphemusin I) was observed in some resistant mutants. Previous studies showed that extracellular protease-mediated degradation of AMPs induced bacterial resistance to AMPs. Our results indicated that the resistance mechanism of P. aeruginosa was not entirely dependent on extracellular proteolytic degradation of tachyplesin I; however, tachyplesin I could induce increased proteolytic activity in P. aeruginosa Most importantly, our findings raise serious concerns about the long-term risks associated with the development and clinical use of tachyplesin I.

Mechanism of tachyplesin I injury to bacterial membranes and intracellular enzymes, determined by laser confocal scanning microscopy and flow cytometry

Tachyplesin I is a 17 amino acid, cationic, antimicrobial peptide with a typical cyclic antiparallel β-sheet structure. Interactions of tachyplesin I with living bacteria are not well understood, although models have been used to elucidate how tachyplesin I permeabilizes membranes. There are several questions to be answered, such as (i) how does tachyplesin I kill bacteria after it penetrates the membrane and (ii) does bacterial death result from the inactivation of intracellular esterases as well as cell injury? In this study, the dynamic antibacterial processes of tachyplesin I and its interactions with Escherichia coli and Staphylococcus aureus were investigated using laser confocal scanning microscopy in combination with electron microscopy. The effects of tachyplesin I on E. coli cell membrane integrity, intracellular enzyme activity, and cell injury and death were investigated by flow cytometric analysis of cells following single- or double-staining with carboxyfluorescein diacetate or propidium iodide. The results of microscopy indicated that tachyplesin I kills bacteria by acting on the cell membrane and intracellular contents, with the cell membrane representing the primary target. Microscopy results also revealed that tachyplesin I uses different modes of action against E. coli and S. aureus. The results of flow cytometry showed that tachyplesin I caused E. coli cell death mainly by compromising cell membrane integrity and causing the inactivation of intracellular esterases. Flow cytometry also revealed dynamic changes in the different subpopulations of cells with increase in tachyplesin I concentrations. Bacteria exposed to 5 μg/mL of tachyplesin I did not die instantaneously; instead, they died gradually via a sublethal injury. However, upon exposure to 10-40 μg/mL of tachyplesin I, the bacteria died almost immediately. These results contribute to our understanding of the antibacterial mechanism employed by tachyplesin I.

Cloning and enhancing production of a detergent- and organic-solvent-resistant nattokinase from Bacillus subtilis VTCC-DVN-12-01 by using an eight-protease-gene-deficient Bacillus subtilis WB800

Background

Nattokinases/Subtilisins (EC 3.4.21.62) belong to the second large family of serine proteases, which gain significant attention and play important role in many biotechnology processes. Thus, a number of nattokinases/subtilisins from various Bacillus species, especially from B. subtilis strains, extensively have been investigated to understand their biochemical and physical properties as well as to improve the production for industrial application. The purpose of this study was to clone a nattokinase gene from Bacillus subtilis strain VTCC-DVN-12-01, enhance its production in B. subtilis WB800, which is deficient in eight extracellular proteases and characterize its physicochemical properties for potential application in organic synthesis and detergent production.

Results

A gene coding for the nattokinase (Nk) from B. subtilis strain VTCC-DVN-12-01 consisted of an ORF of 1146 nucleotides, encoding a pre-pro-protein enzyme (30-aa pre-signal peptide, 76-aa pro-peptide and 275-aa mature protein with a predicted molecular mass of 27.7 kDa and pI 6.6). The nattokinase showed 98-99% identity with other nattokinases/subtilisins from B. subtilis strains in GenBank. Nk was expressed in B. subtilis WB800 under the control of acoA promoter at a high level of 600 mg protein per liter culture medium which is highest yield of proteins expressed in any extracellular-protease-deficient B. subtilis system till date. Nk was purified to homogeneity with 3.25 fold purification, a specific activity of 12.7 U/mg, and a recovery of 54.17%. The purified Nk was identified by MALDI-TOF mass spectrometry through three peptides, which showed 100% identity to corresponding peptides of the B. subtilis nattokinase (CAC41625). An optimal activity for Nk was observed at 65°C and pH 9. The nattokinase was stable at temperature up to 50°C and in pH range of 5–11 and retained more than 85% of its initial activity after incubation for 1 h. Mg²⁺ activated Nk up to 162% of its activity. The addition of Triton X-100, Tween 20, and Tween 80 showed an activation of Nk up to 141% of its initial activity but SDS strongly inhibited. The enzyme was highly resistant to organic solvents.

Conclusions

Our findings demonstrated that an eight-protease-gene-deficient Bacillus subtilis WB800 could overproduce the nattokinase from B. subtilis VTCC-DVN-12-01. Due to high resistance to detergents and organic solvents of this nattokinase, it could be potentially applied in organic synthesis and detergent production.

Development and characterization of a mouse monoclonal antibody against antimicrobial peptide tachyplesin I

Monoclonal antibodies against tachyplesin I (TP I) were developed to study its mechanisms of activity, a kind of cationic antimicrobial peptides (AMPs), in vivo or in vitro, and to purify TP I from expression products. The synthesized TP I was chemically conjugated with the carrier protein BSA and then injected into BALB/c mice. Positive hybridomas were screened by indirect enzyme-linked immunosorbent assay (ELISA) using TP I and subcloned three times with limiting dilution. Five MAbs effective in detecting the native TP I (named 2D8, 3B8, 5H2, 6B12, and 8F5) were obtained. Isotyping of all obtained MAbs indicated that MAbs 2D8, 3B8, 5H2, and 8F5 belong to IgG1, and MAb 6B12 belongs to IgG2a. Specificity assay showed that MAb 8F5 had almost the same level of specificity to natural TP I, recombinant TP I, and synthesized TP I and TP II, but did not cross-react with control peptides. These results suggest that the synthetic AMP conjugates can elicit antibodies against native AMPs and can be used to detect antimicrobial peptides.