The COVID-19 and mpox crisis has reminded the world of the potentially catastrophic consequences of biological agents. Aside from the natural risk, biological agents can also be weaponized or used for bioterrorism. Dissemination in a population or among livestock could be used to destabilize a nation by creating a climate of terror, by negatively impacting the economy and undermining institutions. The Centers for Disease Control and Prevention (CDC) classify biological agents into three categories (A or Tier 1, B and C) according to the risk they pose to the public and national security. Category A or Tier 1 consists of the six pathogens with the highest risk to the population (Bacillus anthracis, Yersinia pestis, Francisella tularensis, botulinum neurotoxins, smallpox and viral hemorrhagic fevers). Several medical countermeasures, such as vaccines, antibodies and chemical drugs, have been developed to prevent or cure the diseases induced by these pathogens. This review presents an overview of the primary medical countermeasures, and in particular, of the antibodies available against the six pathogens on the CDC’s Tier 1 agents list, as well as against ricin.

The development of new and effective antimicrobial compounds is urgent due to the emergence of resistant bacteria. Natural plant flavonoids are known to be effective molecules, but their activity and selectivity have to be increased. Based on previous aurone potency, we designed new aurone derivatives bearing acetamido and amino groups at the position 5 of the A ring and managing various monosubstitutions at the B ring. A series of 31 new aurone derivatives were first evaluated for their antimicrobial activity with five derivatives being the most active (compounds 10, 12, 15, 16, and 20). The evaluation of their cytotoxicity on human cells and of their therapeutic index (TI) showed that compounds 10 and 20 had the highest TI. Finally, screening against a large panel of pathogens confirmed that compounds 10 and 20 possess large spectrum antimicrobial activity, including on bioweapon BSL3 strains, with MIC values as low as 0.78 µM. These results demonstrate that 5-acetamidoaurones are far more active and safer compared with 5-aminoaurones, and that benzyloxy and isopropyl substitutions at the B ring are the most promising strategy in the exploration of new antimicrobial aurones.

Cystic fibrosis (CF)-associated lung infections caused by Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) remain difficult to treat due to multidrug resistance and the redox instability of the pulmonary environment, which can impair antibiotic efficacy. In this study, we investigated alvinellacin (ALV), a disulfide-stabilized β-hairpin antimicrobial peptide (AMP) derived from the deep-sea polychaete Alvinella pompejana (A. pompejana), as a potential therapeutic agent naturally adapted to redox-fluctuating conditions. The antibacterial and antibiofilm activities of ALV were evaluated against multidrug-resistant (MDR) clinical isolates under CF-like reducing conditions (6 mM dithiothreitol (DTT)). Circular dichroism (CD) analysis showed that DTT did not alter the β-hairpin secondary structure of ALV, supporting its structural stability in CF-like environments. Mechanistic analyses included pore-forming assay, membrane interaction studies, scanning electron microscopy (SEM), lipid-binding assays, cytotoxicity testing, and resistance induction assays, while in vivo efficacy was assessed using the Galleria mellonella infection model. ALV demonstrated strong bactericidal activity that was maintained in the presence of NaCl or human serum. ALV did not induce bacterial resistance and effectively inhibited early-stage biofilm formation and disrupted preformed biofilms, including those of the clinical isolate, even under reducing conditions. The peptide showed selective permeabilization of bacterial membranes linked to its stronger affinity for bacterial membrane lipids and negligible interaction with host-like membranes, with no observed cytotoxicity. In vivo, ALV significantly improved survival in infected larvae. These findings highlight ALV as a promising redox-resilient antimicrobial candidate for treating MDR CF lung infections.

The development of new and effective antimicrobial compounds is an urgent need with the emergence of resistant bacteria. Natural plant flavonoids are known to be effective molecules but their activity and selectivity have to be increased. Based on previous aurone potency, we designed new aurone derivatives bearing acetamido and amino groups at the position 5 of the A ring and managing various monosubstitutions at the B ring. A series of 31 new aurone derivatives were first evaluated for their antimicrobial activity with five derivatives being the most active (compounds 10, 12, 15, 16, and 20). The evaluation of their cytotoxicity on human cells and of their therapeutic index (TI) showed that compounds 10 and 20 have the highest TI. Finally, screening against a large panel of pathogens confirmed that compounds 10 and 20 possess a large spectrum antimicrobial activity, including on bioweapon BSL3 strains, with MIC values as low as 0.78 µM. These results demonstrate that 5-acetamidoaurones are far more active and safest compared with 5-aminoaurones, and that benzyloxy and isopropyl substitutions at the B ring are the most promising strategy in the exploration of new antimicrobial aurones.

Trimethoprim–sulfamethoxazole (SXT) remains central to melioidosis eradication therapy, yet the genetic basis of resistance evolution in Burkholderia pseudomallei is not fully defined. Using Burkholderia thailandensis as a biosafe surrogate, we subjected populations to stepwise in vitro evolution under increasing SXT concentrations. Whole-genome sequencing revealed rapid population diversification followed by selective sweeps leading to fixation of fitter resistant variants. Early adaptation involved mutations in regulators of RND efflux systems and folate-associated genes, consistent with multifactorial resistance. Despite this heterogeneity, all evolutionary trajectories converged on a single nonsynonymous substitution, I99L, in dihydrofolate reductase (DHFR/FolA), which rose to fixation at high SXT concentrations. This substitution mirrors changes reported in SXT-resistant B. pseudomallei isolates from chronic infections. Allelic reconstruction demonstrated that Bt-DHFR(I99L) is sufficient to confer a 4- to 16-fold increase in trimethoprim MIC. Biochemical and structural analyses showed preserved catalytic activity but reduced trimethoprim binding, consistent with an allosteric resistance mechanism. Together, these findings establish DHFR as a dominant evolutionary target under SXT pressure and support B. thailandensis as a robust model for dissecting resistance evolution in B. pseudomallei.