Chloramphenicol O-acetyltransferase

Chloramphenicol O-acetyltransferase (CAT) is an enzyme that catalyzes the acetylation of chloramphenicol, a broad-spectrum antibiotic, rendering it inactive. This enzyme plays a significant role in bacterial resistance to chloramphenicol and is of considerable interest in both clinical and molecular biology fields. The presence of CAT in bacteria is a primary mechanism by which these organisms defend themselves against the antibiotic effects of chloramphenicol.

Function

Chloramphenicol O-acetyltransferase works by transferring an acetyl group from acetyl-CoA to one or both of the hydroxyl groups on chloramphenicol. This modification inhibits the binding of chloramphenicol to the bacterial ribosome, thereby preventing the antibiotic from interfering with protein synthesis. As a result, bacteria expressing this enzyme can grow and proliferate even in the presence of chloramphenicol.

Genetics

The gene encoding chloramphenicol O-acetyltransferase, commonly referred to as cat, can be found on both bacterial chromosomes and plasmids. Its presence on plasmids is particularly noteworthy because it facilitates the horizontal transfer of chloramphenicol resistance among different bacterial species. This has significant implications for the spread of antibiotic resistance.

Clinical Significance

The ability of bacteria to inactivate chloramphenicol via chloramphenicol O-acetyltransferase has had a profound impact on the clinical use of this antibiotic. Although chloramphenicol was once a widely used antibiotic for treating various bacterial infections, the emergence of resistant bacterial strains has limited its use. Today, chloramphenicol is often reserved for serious infections where alternative treatments are not available or are contraindicated.

Biotechnological Applications

In molecular biology, the cat gene is frequently used as a selectable marker to identify transformed cells. Cells that have successfully incorporated the cat gene can be selected for by growing them in the presence of chloramphenicol. Only those cells expressing chloramphenicol O-acetyltransferase will survive, allowing researchers to isolate and study genetically modified organisms.

See Also

• Antibiotic resistance
• Acetyltransferase
• Plasmid
• Protein synthesis