A Novel and Efficient High-Yield Method for Preparing Bacterial Ghosts

Bacteriophage-encoded protein utilization in bacterial ghost production: a mini-review

Bacterial ghosts (BGs) are described as bacterial cell envelopes that retain their structure but lack cytoplasmic contents. The study of BGs spans multiple disciplinary domains, and the development of BG production techniques to obtain ample and stable BG samples holds significant implications for probing the biological characteristics of BGs, devising novel disease treatment strategies, and leveraging their industrial applications. Numerous products encoded within bacteriophage (phage) genomes possess the capability to lyse bacteria, thereby inducing BG formation primarily via disruption of bacterial cell wall integrity. This review comprehensively surveys the utilization of phage-encoded proteins in BG production techniques, encompassing methodologies such as phage E protein-mediated lysis, perforin protein-induced lysis, and strategies combining E protein with holin-endolysin systems. Additionally, discussions and summaries are provided on the current applications, challenges, and modification strategies associated with different techniques. Through a focused exploration of BG production techniques, with an emphasis on precise manipulation of BG formation using phage-encoded protein technologies, this study aims to furnish robust tools and methodologies for delving into the mechanisms underlying BG formation, as well as for the development of novel therapeutic strategies and applications based on BGs.

Construction and Mechanism Exploration of Highly Efficient System for Bacterial Ghosts Preparation Based on Engineered Phage ID52 Lysis Protein E

Bacterial ghosts (BGs) are hollow bacterial cell envelopes with intact cellular structures, presenting as promising candidates for various biotechnological and biomedical applications. However, the yield and productivity of BGs have encountered limitations, hindering their large-scale preparation and multi-faceted applications of BGs. Further optimization of BGs is needed for the commercial application of BG technology. In this study, we screened out the most effective lysis protein ID52-E-W4A among 13 mutants based on phage ID52 lysis protein E and optimized the liquid culture medium for preparing Escherichia coli Nissle 1917 (EcN). The results revealed a significantly higher lysis rate of ID52-E-W4A compared to that of ID52-E in the 2xYT medium. Furthermore, EcN BGs were cultivated in a fermenter, achieving an initial OD600 as high as 6.0 after optimization, indicating enhanced BG production. Moreover, the yield of ID52-E-W4A-induced BGs reached 67.0%, contrasting with only a 3.1% yield from φX174-E-induced BGs. The extended applicability of the lysis protein ID52-E-W4A was demonstrated through the preparation of Salmonella pullorum ghosts and Salmonella choleraesuis ghosts. Knocking out the molecular chaperone gene slyD and dnaJ revealed that ID52-mediated BGs could still undergo lysis. Conversely, overexpression of integral membrane enzyme gene mraY resulted in the loss of lysis activity for ID52-E, suggesting that the lysis protein ID52-E may no longer rely on SlyD or DnaJ to function, with MraY potentially being the target of ID52-E. This study introduces a novel approach utilizing ID52-E-W4A for recombinant expression, accelerating the BG formation and thereby enhancing BG yield and productivity.

Topical drug delivery strategies for enhancing drug effectiveness by skin barriers, drug delivery systems and individualized dosing

Topical drug delivery is widely used in various diseases because of the advantages of not passing through the gastrointestinal tract, avoiding gastrointestinal irritation and hepatic first-pass effect, and reaching the lesion directly to reduce unnecessary adverse reactions. The skin helps the organism to defend itself against a huge majority of external aggressions and is one of the most important lines of defense of the body. However, the skin's strong barrier ability is also a huge obstacle to the effectiveness of topical medications. Allowing the bioactive, composition in a drug to pass through the stratum corneum barrier as needed to reach the target site is the most essential need for the bioactive, composition to exert its therapeutic effect. The state of the skin barrier, the choice of delivery system for the bioactive, composition, and individualized disease detection and dosing planning influence the effectiveness of topical medications. Nowadays, enhancing transdermal absorption of topically applied drugs is the hottest research area. However, enhancing transdermal absorption of drugs is not the first choice to improve the effectiveness of all drugs. Excessive transdermal absorption enhances topical drug accumulation at non-target sites and the occurrence of adverse reactions. This paper introduces topical drug delivery strategies to improve drug effectiveness from three perspectives: skin barrier, drug delivery system and individualized drug delivery, describes the current status and shortcomings of topical drug research, and provides new directions and ideas for topical drug research.

Preparation of Escherichia coli ghost of anchoring bovine Pasteurella multocida OmpH and its immunoprotective effect

Pasteurella multocida is a pathogen that can infect humans and animals. A ghost is an empty bacterial body devoid of cytoplasm and nucleic acids that can be efficiently presented by antigen-presenting cells. To study a novel ghost vector vaccine with cross-immune protection, we used bacteriophage PhiX174 RF1 and Pasteurella multocida standard strain CVCC393 as templates to amplify the split genes E and OmpH to construct a bidirectional expression vector E'-OmpH-pET28a-ci857-E. This is proposed to prepare a ghost Escherichia coli (engineered bacteria) capable of attaching and producing Pasteurella multocida OmpH on the inner membrane of Escherichia coli (BL21). The aim is to assess the antibody levels and the effectiveness of immune protection by conducting a mouse immunoprotective test. The bidirectional expression vector E'-OmpH-pET28a-ci857-E was successfully constructed. After induction by IPTG, identification by SDS-PAGE, western blot, ghost culture and transmission electron microscope detection, it was proven that the Escherichia coli ghost anchored to Pasteurella multocida OmpH was successfully prepared. The immunoprotective test in mice showed that the antibody levels of Pasteurella multocida inactivated vaccine, OmpH, ghost (aluminum glue adjuvant) and ghost (Freund's adjuvant) on day 9 after immunization were significantly different from those of the PBS control group (P < 0.01). The immune protection rates were 100%, 80%, 75%, and 65%, respectively, and the PBS negative control was 0%, which proved that they all had specific immune protection effects. Therefore, this study lays the foundation for the further study of ghosts as carriers of novel vaccine-presenting proteins.

Prodigiosin-Functionalized Probiotic Ghosts as a Bioinspired Combination Against Colorectal Cancer Cells

Lactobacillus acidophilus ghosts (LAGs) with the unique safety of a probiotic, inherent tropism for colon cells, and multiple bioactivities offer promise as drug carriers for colon targeting. Our objective was to evaluate LAGs functionalized with prodigiosin (PG), apoptotic secondary bacterial metabolite, as a bioinspired formulation against colorectal cancer (CRC). LAGs were prepared by a chemical method and highly purified by density gradient centrifugation. LAGs were characterized by microscopic and staining techniques as relatively small-sized uniform vesicles (≈1.6 µm), nearly devoid of cytoplasmic and genetic materials and having a negatively charged intact envelope. PG was highly bound to LAGs envelope, generating a physiologically stable bioactive entity (PG-LAGs), as verified by multiple microscopic techniques and lack of PG release under physiological conditions. PG-LAGs were active against HCT116 CRC cells at both the cellular and molecular levels. Cell viability data highlighted the cytotoxicity of PG and LAGs and LAGs-induced enhancement of PG selectivity for HCT116 cells, anticipating dose reduction for PG and LAGs. Molecularly, expression of the apoptotic caspase 3 and P53 biomarkers in HCT116 intracellular proteins was significantly upregulated while that of the anti-apoptotic Bcl-2 (B-cell lymphoma 2) was downregulated by PG-LAGs relative to PG and 5-fluorouracil. PG-LAGs provide a novel bacteria-based combination for anticancer biomedicine.

Construction and In Vitro Evaluation of a Tumor Acidic pH-Targeting Drug Delivery System Based on Escherichia coli Nissle 1917 Bacterial Ghosts

Synthetic nanocarriers are a promising therapeutic delivery strategy. However, these systems are often hampered by inherent disadvantages such as strong biotoxicity and poor biocompatibility. To overcome these issues, biological carriers with commonly used chemotherapy drugs have been developed. In this work, engineered bacterial ghosts (BGs) originated from probiotic Escherichia coli Nissle 1917 (EcN) were devised to specifically target acidic extracellular environments of tumor tissue. To improve the production efficiency and safety, a novel lysis protein E from phage α3 was applied to produce EcN BGs under high growth densities in high quality. In addition, the acidity-triggered rational membrane (ATRAM) peptides were displayed in EcN BGs to facilitate specific cancer cell internalization within the acidic tumor microenvironment before drug release. In conclusion, the engineered EcN BGs offer a promising means for bionic bacteria construction for hepatocellular carcinoma therapy.

Efficient Robust Yield Method for Preparing Bacterial Ghosts by Escherichia coli Phage ID52 Lysis Protein E

Bacterial ghosts (BGs) are nonliving empty bacterial shells without cytoplasm retaining original morphology and identical antigenicity of natural bacteria, making them high potential and promising vaccine candidates and delivery vehicles. However, the low yield of commonly used BGs preparation methods limits its mass production and widely application. In order to improve BGs production, E. coli phage ID52 lysis protein E was introduced to generating BGs for the first time. Above all, we compared the lysis activity of lysis protein of E. coli phage φX174 and E. coli phage ID52 as well as the effects of promoters on the lysis activity of ID52-E, which shown that the lysis activity and BGs formation rate of protein ID52-E was significantly higher than protein φX174-E. Further, the lysis activity of ID52-E was significantly improved under the control of L-arabinose inducible promoter which initial induction OD₆₀₀ reached as high as 2.0. The applicability of lysis protein ID52-E induced by L-arabinose was proved by preparing probiotic E. coli Nissle 1917 BGs and pathogenic Salmonella typhimurium BGs in mass production. This paper introduced a novel and highly efficient method for BGs preparation depending on recombinant expression of E. coli phage ID52-E under eco-friendly and reasonable price inducer L-arabinose.

Protective Immunity against Listeria monocytogenes in Rats, Provided by HCl- and NaOH-Induced Listeria monocytogenes Bacterial Ghosts (LMGs) as Vaccine Candidates

Listeria monocytogenes (Lm) bacterial ghosts (LMGs) were produced by the minimum inhibitory concentration (MIC) of HCl, H₂SO₄, and NaOH. Acid and alkali effects on the LMGs were compared by in vitro and in vivo analyses. Scanning electron microscope showed that all chemicals form lysis pores on the Lm cell envelopes. Real-time qPCR revealed a complete absence of genomic DNA in HCl- and H₂SO₄-induced LMGs but not in NaOH-induced LMGs. HCl-, H₂SO₄- and NaOH-induced LMGs showed weaker or missing protein bands on SDS-PAGE gel when compared to wild-type Lm. Murine macrophages exposed to the HCl-induced LMGs showed higher cell viability than those exposed to NaOH-induced LMGs or wild-type Lm. The maximum level of cytokine expression (TNF-α, iNOS, IFN-γ, and IL-10 mRNA) was observed in the macrophages exposed to NaOH-induced LMGs, while that of IL-1β mRNA was observed in the macrophages exposed to HCl-induced LMGs. To investigate LMGs as a vaccine candidate, mice were divided into PBS buffer-injected, HCl- and NaOH-induced LMGs immunized groups. Mice vaccinated with HCl- and NOH-induced LMGs, respectively, significantly increased in specific IgG antibodies, bactericidal activities of serum, and CD4⁺ and CD8⁺ T-cell population. Antigenic Lm proteins reacted with antisera against HCl- and NOH-induced LMGs, respectively. Bacterial loads in HCl- and NaOH-induced LMGs immunized mice were significantly lower than PBS-injected mice after virulent Lm challenges. It suggested that vaccination with LMGs induces both humoral and cell-mediated immune responses and protects against virulent challenges.