Insights into the Spectrum of Activity and Mechanism of Action of MGB-BP-3.

MGB-BP-3 is a potential first-in-class antibiotic, a Strathclyde Minor Groove Binder (S-MGB), that has successfully completed Phase IIa clinical trials for the treatment of Clostridioides difficile associated disease. Its precise mechanism of action and the origin of limited activity against Gram-negative pathogens are relatively unknown. Herein, treatment with MGB-BP-3 alone significantly inhibited the bacterial growth of the Gram-positive, but not Gram-negative, bacteria as expected. Synergy assays revealed that inefficient intracellular accumulation, through both permeation and efflux, is the likely reason for lack of Gram-negative activity. MGB-BP-3 has strong interactions with its intracellular target, DNA, in both Gram-negative and Gram-positive bacteria, revealed through ultraviolet-visible (UV-vis) thermal melting and fluorescence intercalator displacement assays. MGB-BP-3 was confirmed to bind to dsDNA as a dimer using nano-electrospray ionization mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy. Type II bacterial topoisomerase inhibition assays revealed that MGB-BP-3 was able to interfere with the supercoiling action of gyrase and the relaxation and decatenation actions of topoisomerase IV of both Staphylococcus aureus and Escherichia coli. However, no evidence of stabilization of the cleavage complexes was observed, such as for fluoroquinolones, confirmed by a lack of induction of DSBs and the SOS response in E. coli reporter strains. These results highlight additional mechanisms of action of MGB-BP-3, including interference of the action of type II bacterial topoisomerases. While MGB-BP-3's lack of Gram-negative activity was confirmed, and an understanding of this presented, the recognition that MGB-BP-3 can target DNA of Gram-negative organisms will enable further iterations of design to achieve a Gram-negative active S-MGB.

Early onset and long lasting protection in pigs provided by a classical swine fever E2-vaccine candidate produced in the milk of goats.

For vaccination against classical swine fever virus (CSFV), it is strongly desirable to induce a rapid and long lasting protection. At present, only live attenuated CSFV vaccines have shown early onset of protection, differing with the recombinant subunit-based vaccines reported so far. Recently, a new vaccine formulation based on E2 envelope viral glycoprotein produced in the milk of goats (E2his) has been shown to induce a highly protective response in pigs against CSFV infection. Pigs immunized with a single dose of this vaccine candidate, formulated as a water-in oil emulsion, elicited an effective response against CSF as early as 7 days post-vaccination. No severe CSF clinical signs were observed and no animals died although the challenge dose was 10(5)PDL(50) of a highly pathogenic CSFV strain. Noticeably, this response completely prevented CSFV infection in pigs when they were challenged under the same conditions 2 weeks after a single dose of the recombinant E2his vaccine formulation. A schedule consisting of a primary immunization with the same vaccine candidate, followed by a booster dose 2 weeks later induced a highly protective response against CSFV infection for as long as 9 months post-vaccination. These promising results demonstrate by far the feasibility of using the E2his-based vaccine in regional programs for preventing and controlling CSF.