Chloramphenicol

Chemical structure: phenicole

Chloramphenicol is a synthetic antibiotic, isolated from strains of Streptomyces venezuelae. It is often used for bacterial selection in molecular biology applications at 10-20 μg/mL and as a selection agent for transformed cells containing chloramphenicol reistance genes.

Mode of Action: Chloramphenicol inhibits bacterial protein synthesis by blocking the peptidyl transferase step by binding to the 50S ribosomal subunit and preventing attachment of aminoacyl tRNA to the ribosome. It also inhibits mitochondrial and chloroplast protein synthesis and ribosomal formation of (p)ppGpp, de-pressing rRNA transcription.

Mode of Resistance: Use of chloramphenicol acetyltransferase will acetylate the product and inactivate it.

Antimicrobial Spectrum: This is a broad spectrum antibiotic against gram-positive and gram-negative bacteria, and is used mainly for ophthalmic and veterinary purposes.

Stock solutions should be stored at 2-8°C and are stable at 37°C for 5 days. Aqueous solutions are neutral and stable over a wide pH range, with 50% hydrolysis occurring after 290 days. Use of a borax buffered solution reduces this number to 14%. Solutions should be protected from light as photochemical decomposition results in a yellowing of the solution. Heating aqueous solutions at 115°C for 30 minutes results in a 10% loss of chloramphenicol.

Stock solutions can be prepared directly in the vial at any recommended concentration. A solution at 50 mg/mL in ethanol yields a clear, very faint, yellow solution. Degradation of chloramphenicol in aqueous solution is catalyzed by general acids and bases. This rate of degradation is independent of the ionic strength and pH.