Tackling antibiotic resistance with precision gene editing
Image provided by Cell Press: "Role of CRISPR-Cas systems and anti-CRISPR proteins in bacterial antibiotic resistance” (Kadkhoda et al., 2024)
The rise of antibiotic-resistant "superbugs" is one of the most pressing challenges in modern medicine. The World Health Organization (WHO) has declared antibiotic resistance a global health emergency, warning that without urgent action, routine infections and minor injuries could once again become life-threatening.
Antibiotic resistance is when bacteria, as they evolve, develop resistance to chemicals previously designed to kill them. Antibiotic resistance genes are often located on Mobile Genetic Elements and can spread among bacteria through Horizontal Gene Transfer(HGT).
Image provided by Spartha Medical.
HGT is the sharing of genetic materials among organisms that are not in a parent-offspring relationship. It contributes to the spread of ARGs (responsible for antibiotic resistance) through mechanisms like transformation (uptake of free DNA), transduction (phage-mediated transfer) and conjugation (plasmid-mediated transfer). Bacteria evolve quickly (in a matter of weeks) and share resistant mechanisms; this, combined with the overuse of antibiotics in healthcare, has accelerated the emergence of superbugs.
Routine treatments against infections caused by Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, etc. fail, resulting in prolonged illnesses, increased healthcare costs, and higher mortality rates.
Conventional antibiotic discovery/invention techniques are slow, resource-intensive and cannot meet the demands of the ever-growing population; therefore, researchers have turned to genome editing techniques like CRISPR/cas9, which offer many advantages.
Image provided by ResearchGate: “CRISPR-Cas9 for in vivo Gene Therapy: Promise and Hurdles” (Dai et al., 2016)
CRISPR- Clustered Regularly Interspaced Short Palindromic Repeats
The foundational discoveries leading to the development of CRISPR-Cas9 technology date back to 1987, when palindromic segments of DNA in bacteria were first identified. In 2007, researchers showed that CRISPR plays an important role in microbial innate immunity. In 2012, research groups of Doudna and Charpentier collaboratively deduced that the CRISPR cleavage mechanism involves RNA guiding Cas9. CRISPR-based genome editing requires two components: a guide RNA and a CRISPR-associated endonuclease protein (Cas). The guide RNA, analogous to a GPS system, directs the Cas nuclease to the specific target DNA sequence, which then cuts the DNA at that site. The most commonly used nuclease, SpCas9, is the one isolated from Streptococcus pyogenes. SpCas9 has 2 lobes, one for recognition and the other for cleavage( nuclease lobe). Upon binding to the target DNA with the help of guide RNA, the recognition lobe checks for complementarity and the nuclease lobe cleaves at the specific site causing double-stranded breaks (DSB). The cell tries to repair these breaks through Non-Homologous End Joining (NHEJ) or Homology Directed Repair(HDR) mechanisms.
The CRISPR system for editing human and mouse cell genomes was first used in 2013.
Since it specifically targets and cleaves DNA sequences encoding ARGs, CRISPR/Cas system has been developed into a new gene-editing tool for the prevention and control of bacterial drug resistance. It has a potentially important role in limiting HGT. For example, the I-F CRISPR-Cas system in Pseudomonas aeruginosa removed resistance genes or plasmids, thereby reducing the level of antibiotic resistance of the bacteria.
CRISPR-Cas9 is a promising strategy to combat antibiotic resistance. However, advancements in delivery systems, such as phage-mediated CRISPR/nanoparticle vectors and a higher degree of specificity are necessary for clinical success. Ethical concerns, such as unintended ecological impacts and equitable access, must be taken into consideration as well. With responsible development, CRISPR has the potential to revolutionize antibiotic resistance management, providing a sustainable, precision-based solution to the superbug crisis.
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