Editing Antibiotic (section)

==== 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.<ref name="pmid29358495">{{cite journal | vauthors = Ishino Y, Krupovic M, Forterre P | title = History of CRISPR-Cas from Encounter with a Mysterious Repeated Sequence to Genome Editing Technology | journal = Journal of Bacteriology | volume = 200 | issue = 7 | pages = e00580-17 | date = April 2018 | pmid = 29358495 | pmc = 5847661 | doi = 10.1128/JB.00580-17 }}</ref>

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 [[antimicrobial resistance|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.<ref name="pmid31295426"/><ref name="pmid30683453"/> This approach has successfully been used to [[Gene silencing|silence]] antibiotic resistance and reduce the virulence of [[Shigatoxigenic and verotoxigenic Escherichia coli|enterohemorrhagic ''E. coli'']] in an ''in vivo'' model of infection.<ref name="pmid30683453"/>