Combinations of early generation antibiotics and antimicrobial peptides are effective against a broad spectrum of bacterial biothreat agents

The misuse of infectious disease pathogens as agents of deliberate attack on civilians and military personnel is a serious national security concern, which is exacerbated by the emergence of natural or genetically engineered multidrug resistant strains. In this study, the therapeutic potential of combinations of an antibiotic and a broad-spectrum antimicrobial peptide (AMP) was evaluated against five bacterial biothreats, the etiologic agents of glanders (Burkholderia mallei), melioidosis (Burkholderia pseudomallei), plague (Yersinia pestis), tularemia (Francisella tularensis), and anthrax (Bacillus anthracis). The therapeutics included licensed early generation antibiotics which are now rarely used. Three antibiotics and one 24- amino acid AMP were selected based on MIC assay data. Combinations of the AMP and tigecycline, minocycline, or novobiocin were screened for synergistic activity by checkerboard MIC assay. The combinations each enhanced the susceptibility of several strains. The tetracycline-peptide combinations increased the sensitivities of Y. pestis, F. tularensis, B. anthracis and B. pseudomallei, and the novobiocin-AMP combination augmented the sensitivity of all five. In time-kill assays, down-selected combinations of the peptide and minocycline or tigecycline enhanced killing of B. anthracis, Y. pestis, F. tularensis, and Burkholderia mallei but not B. pseudomallei. The novobiocin-AMP pair significantly reduced viability of all strains except B. mallei, which was very sensitive to the antibiotic alone. The results suggested that antibiotic-AMP combinations are useful tools for combating diverse pathogens. Future studies employing cell culture and animal models will utilize virulent strains of the agents to investigate the in vivo availability, host cytotoxicity, and protective efficacy of these therapeutics.

Characterization of the immune response elicited by the vaccinia virus L3 protein delivered as naked DNA

Poxviruses are complex dsDNA viruses with over 200 genes, many of them with unknown role in the stimulation of immune responses. Among these, the vaccinia virus (VACV) L3L ORF encodes an essential protein for the transcription of the VACV early genes. To the best of our knowledge, the immune response elicited by L3 has not been characterized. In this regard, our data describes a DNA L3-coding plasmid (pL3L) that stimulates both, humoral- and cell-mediated immune responses in a mouse model. Cell-mediated immune responses were measured by IFN-γ and IL-4 ELISPOT assays. We performed CD8⁺ cells depletion and flow cytometry analysis to account for the contribution of cytotoxic T lymphocytes in the IFN-γ production. Moreover, results from ELISPOT were confirmed by measuring the concentration of IL-4 and IFN-γ in supernatant of antigen-stimulated splenocytes by cytokine ELISA. Additionally, dominant antigenic regions of L3 protein were identified by epitope mapping analysis. Humoral immune responses were assessed by ELISA. Specifically, the production of total IgG, IgG1 (TH-2) and IgG2a (TH-1) were determined one week after the final immunization. Our ELISPOT data shows pL3L-immunized animals to produce significantly higher frequencies of IFN-γ Spot-Forming Cells (SFC) versus controls. IL-4 levels remained unchanged in all three groups, demonstrating the increase in antigen-specific IFN-γ releasing cells. Flow cytometry assay results showed that CD8⁺ T cells are a major contributor to the production of IFN-γ. Moreover, our formulation enhances the production of total IgG, predominantly IgG2a isotype. Immunization with pL3L promotes a robust cytotoxic immune response, crucial against viral pathogens. In addition, our vaccine candidate promotes an increase in IgG levels, especially IgG2a (TH-1 type). Our data encourages further studies of L3 as a novel antigen in vaccine development against poxviruses.

Utilizing Ayurvedic literature for the identification of novel phytochemical inhibitors of botulinum neurotoxin A

ETHNOPHARMACOLOGICAL RELEVANCE

Ayurveda, an ancient holistic system of health care practiced on the Indian subcontinent, utilizes a number of multi-plant formulations and is considered by many as a potential source for novel treatments, as well as the identification of new drugs. Our aim is to identify novel phytochemicals for the inhibition of bacterial exotoxin, botulinum neurotoxin A (BoNT/A) based on Ayurvedic literature. BoNT/A is released by Clostridium species, which when ingested, inhibits the release of acetylcholine by concentrating at the neuromuscular junction and causes flaccid paralysis, resulting in a condition termed as botulism, and may also lead to death due to respiratory arrest.

METHODS

Fifteen plants were selected from the book 'Diagnosis and treatment of diseases in Ayurveda' by Vaidya Bhagwan Dash and Lalitesh Kashyap, based on their frequency of use in the formulations used for the treatment of six diseases with neuromuscular symptoms similar to botulism. Phytochemicals from these plants were screened using in silico, and in vitro methods. Structures of 570 reported phytochemicals from 14 plants were docked inside six reported BoNT/A light chain crystal structures using ensemble docking module in Maestro (Schrödinger, LLE).

RESULTS

From the docking scores and structural diversity, nine compounds including acoric acid 1, three flavonoids, three coumarins derivatives, one kava lactone were selected and screened using an in vitro HPLC-based protease assay. The bioassay results showed that several compounds possess BoNT/A LC inhibition of 50-60% when compared to positive controls NSC 84094 and CB7967495 (80-95%).

CONCLUSION

Further testing of the active compounds identified from Ayurvedic literature and structure-activity studies of acoric acid 1 using more sensitive bioassays is under way. The identification of acoric acid 1, a novel scaffold against BoNT/A, exemplifies the utility of Ayurvedic literature for the discovery of novel drug leads.