section_path: Antibiotic pipeline/Replenishing the antibiotic pipeline and developing other new therapies/CRISPR-Cas9-based treatments
section_name: CRISPR-Cas9-based treatments
paragraph_text: CRISPR-Cas9-based treatments
  
  In the early 2000s, a system was discovered that enables bacteria to defend themselves against invading viruses. The system, known as CRISPR-Cas9, consists of (a) an enzyme that destroys DNA (the nuclease Cas9) and (b) the DNA sequences of previously encountered viral invaders (CRISPR). These viral DNA sequences enable the nuclease to target foreign (viral) rather than self (bacterial) DNA.
  
  Although the function of CRISPR-Cas9 in nature is to protect bacteria, the DNA sequences in the CRISPR component of the system can be modified so that the Cas9 nuclease targets bacterial resistance genes or bacterial virulence genes instead of viral genes. The modified CRISPR-Cas9 system can then be administered to bacterial pathogens using plasmids or bacteriophages. This approach has successfully been used to silence antibiotic resistance and reduce the virulence of enterohemorrhagic E. coli in an in vivo model of infection.