CRISPR-BASED ENGINEERING OF BACTERIOPHAGES AGAINST ANTIBIOTIC-RESISTANT BACTERIA

Abstract

Antimicrobial resistance is now a leading infectious cause of death worldwide, and the small-molecule pipeline is not replacing the drugs it is eroding. Bacteriophages offer a self-amplifying, narrow-spectrum alternative unaffected by the mechanisms that disable antibiotics, but wild phages are poorly matched to clinical requirements: host range is too narrow, bacteria escape within hours, temperate phages carry lysogeny and virulence cargo, and their genomes long resisted deliberate modification. CRISPR-Cas changed this twice over. It supplied a counterselection method efficient enough to make phage genomes routinely editable, turning phage therapy from a screening exercise into a design discipline; and it supplied a payload — a programmable nuclease that, delivered into a bacterium and aimed at its chromosome or a resistance plasmid, kills or disarms that cell by sequence rather than by biochemical class. Combining the two gives an agent whose host range, resistance profile and kill mechanism are all specified in DNA. This review covers the mechanistic basis of CRISPR self-targeting; the toolbox for editing phage genomes; design strategies including receptor-binding protein swapping, lysogeny deletion and anti-CRISPR counter-defence; the delivery problem that remains the field's binding constraint; the clinical pipeline, where engineered CRISPR-phages have now completed controlled human trials; and Pakistan as a regional case study in which XDR typhoid presents an unusually well-matched target. We conclude that the engineering is largely solved and that delivery, pharmacology and manufacturing now determine the pace.