The WHO and the EU have recognized the One-Health concept; thus, human, animal, and environmental health are tightly connected, and the impact on one affects the others. In the previous decades, the misuse and abuse of antibiotics in human health and intensive farming have led to the appearance of microbial strains that are resistant to known antimicrobials, including last resort ones. With the COVID-19 crisis, antibiotics were prescribed to about 70% of the patients. However, only a 10% really needed it, with the subsequent risk of emergence of bacterial superpathogens. Since human-animal zoonosis is a key factor for pathogen spread in pandemies, it is essential to develop new strategies that address both human and animal health, and at the same time ensure farm production and food security.
One of the key issues in the search for new antimicrobials is their selectivity; since in many cases they affect the beneficial microbiota, which is vital for a long-term good general health and plays a crucial role to control pathogens and avoid virulence against the host. Furthermore, a generalized action against the microbial ecosystems puts a high evolutionary pressure towards the appearance of resistances, and once a resistant strain has evolved (pathogenic or not), it can transfer its resistance genome to other microorganisms, eventually reaching different pathogens. The horizontal acquisition of antimicrobial resistance is often due to bacterial conjugation, where mobile genetic elements such as conjugative plasmids are transferred.
To address this challenge, two promising strategies have been developed in the last years. The first one is interfering bacterial communication and coordinated responses (quorum sensing), which is essential for virulence, coordinated attacks on the host, and building of microbial-protecting biofilms. With this strategy, microbes are not killed, and thus, the pressure towards resistant strains is greatly reduced.
The second strategy is the development of species-selective antimicrobials, which affect only the desired pathogen while sparing the other microbiota. This strategy includes the development of new selective delivery systems. The project will focus on these new strategies, and their application both to human and animal health.
Therefore, the Subproject 1 (SP1) is oriented towards the development of novel quorum sensing and conjugation inhibitors that are effective against resistant pathogens, by applying our methodologies for the transformation of customizable amino acid units and for the site-selective peptide modification. These methodologies, that generate compound libraries by selective modification of a few starting substrates, would save time and materials in the drug discovery process.
On the other side, the project will develop species-selective antimicrobials by attaching selected peptides and other drugs to species-recognition systems. Thus, the development of hybrids of antimicrobial peptides and bacterial pheromones would allow the selective targeting of pathogens.
Moreover, species-selective delivery systems based on nanoparticles could be developed. Thus, 2,5-diketopiperazine (DKP) scaffolds or dendrimers decorated with pathogen recognition motifs and transporting different sorts of antimicrobials (from our new antimicrobial peptides to natural products and control commercial drugs) would fight the desired pathogens while leaving the beneficial microbiota unharmed.
The effectiveness of these new systems would be tested in vitro not only with EUCAST microbial strains (Subproject 2, SP2), but also with multidrug resistant (MDR) human pathogens from clinical isolates (SP1) and MDR animal pathogens from veterinary practice (SP2). The selected compounds will be also studied in vivo using animal infection models such as the nematode C. elegans (SP1/SP2) and vertebrates (SP2), not only in mice but also in farm animals. Finally, Subproject 2 will test the selectivity of these compounds in two ways. The first approach will compare the effects of the selected agents on the pathogens and on beneficial components of the gut microbiota, such as Lactobacillus and Bifidobacterium. Once these preliminary studies are completed, the most promising compounds will be tried in complex gut microbiota ecosystems, using the model developed by our external advisors in the University of Reading, and already implemented in ULPGC. Thus, a complex microbiota cultured from faeces in a gut model vessel will be treated with the selected agents. The evolution of the microbiota will monitored by cytometry analysis and metagenomic techniques. In this way, the fine-tuning of these ecosystems in the presence of a drug agent will be studied, and the better understanding of microbial interactions will help to the design of more effective, selective quorum sensing inhibitors and antimicrobial systems. These compounds will be able to fight the emerging superpathogens while sparing our allies in the beneficial microbiota.
