Antimicrobial resistance

Molecular Microbiology is happy to offer a collection of of recently published articles that address various aspects of antimicrobial resistance. The entire collection is accessible here. Modern medicine has benefited from the use of antimicrobial drugs to treat infectious diseases caused by bacteria, fungi, parasites and viruses. However, the recurrent use of these drugs in human, animal and environmental settings have contributed to the appearance of antimicrobial resistance (AMR) across different genera. Therefore, it is not surprising that AMR has emerged as one of the biggest threats to public and environmental health in the past 20 years. On one hand we have compiled reviews that give the readers of this special issue a historical perspective into the field (Davies & Behroozian 2020) and their role in the environment (Pishchany & Kolter 2020; Baquero et al., 2020). AMR is associated with the ability of a population (mother cells and its progeny) to survive in the presence of these antimicrobial agents. Mechanisms of AMR seem to be conserved from prokaryotes to eukaryotes and are normally associated with processes that limit the uptake or inactivate an antimicrobial drug, modify the drug target or that actively pump the drug out of the cell. Cells can therefore survive in the presence of antimicrobial drugs by reducing permeability of the outer membrane and the activity of porins and by using/increasing multidrugefflux pumps. Examples of resistance by modulation of porins/efflux pumps are seen in the Gramnegative bacteria Stenotrophomonas maltophilia (Calvopiña et al., 2020), Acinetobacter baumannii (Leus et al., 2020), Pseudomonas aeruginosa (Piselli & Benz 2021) and the fungal pathogen Candida lusitanie (Biermann et al., 2021). Acquisition of antibiotic resistance genes from other organisms' plasmids and conjugative transposons is also linked to AMR. More on the mobile elements and possible recombination mechanisms associated with A. baumannii AMR mechanisms can be read in this issue (Balalovski & Grainge 2020). To survive in the presence of antimicrobial drugs bacteria, fungi and parasites need to be able to sense and respond to their environment. Hence, identifying how these signalling pathways coordinate an effective response against the deleterious effects of antibiotics might provide clues towards the development of novel antimicrobial strategies. Activation of BceS histidine kinases in the Grampositive Bacillus subtilis, for example, signals to ensure that resistance transporters are produced in a drug dosedependent manner with minimum energy costs (Koh et al., 2021). Furthermore, Ca2+ signalling seems to be key in mediating Neurospora crassa resistance to the antifungal peptide PAF26 (Alexander et al., 2020). The understanding of such mechanisms provides the opportunity to identify putative inhibitors either against sensor kinases such as histidine kinases in B. subtilillis or Ca2+ transporters in fungi to abrogate AMR in these organisms. Hence, there is a need for the development of specific antimicrobial compounds that will affect microbes but will pose no threat to its host. In this issue, we highlight work that explores the use of novel antibiotics produced by microorganisms in the warfare against its competitors in the environment (Singh et al., 2020; Yan et al., 2020), the development of programmable RNA antibiotics for microbiome editing (Vogel 2020) and the use of techniques, such as cryoEM, to aid in structurebased drug discovery and vaccine development (Shepherd et al., 2022). From multidrug resistant bacteria to panresistant fungi there is a need for the development of novel antimicrobial strategies. In this special issue, we have compiled articles that mirror the efforts made by this community to understand the basis and mechanisms driving AMR in bacteria, fungi and protozoans and therefore pave the way to possible solutions against the AMR threat that has taken its toll in public health systems and environmental sectors.