Abstract

The discovery of RNA-guided nucleases among the CRISPR associated (Cas) proteins has led to a large number of exciting technological developments. While targeted DNA cleavage in mammalian cells enables accurate genetic modification, the main outcome of Cas cleavage within the bacterial genome is cell death. This observation has enabled researchers to design sequence-specific CRISPR-based antimicrobials. A CRISPR associated nuclease would be delivered to bacteria by modified bacteriophages or conjugative plasmids along with one or several guide RNAs targeting an antibiotic resistance gene or virulence factor. Pathogens carrying that gene would be eliminated without affecting the rest of the microbiome. Beyond targeted bacterial killing, CRISPR antimicrobials could be used to eliminate resistance genes or undesired genetic elements without actually killing the bacteria. They could also be used to immunize bacteria against the acquisition of such genetic elements in the first place. Here we review the mode of action of CRISPR antimicrobials, how they can be delivered to target bacteria and the many challenges that remain to be overcome in order to design effective drugs, including resistance to CRISPR antimicrobials and delivery issues.