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.