Chloramphenicol is a bacteriostatic antimicrobial agent that is effective against a wide variety of microorganisms. Chloramphenicol interferes with microbial protein synthesis by binding to the 50S ribosomal subunit and inhibiting the peptidyltransferase step in protein synthesis.
There are three known mechanisms of resistance to chloramphenicol: reduced membrane permeability; mutation of the 23S ribosomal subunit; and elaboration of chloramphenicol acetyltransferase. Mutations in 23S rRNA have been previously reported in chloramphenicol-resistant strains of E. coli and Ehrlichia.
High-level resistance to chloramphenicol is conferred by the cat gene, which encodes an enzyme called chloramphenicol acetyltransferase that inactivates chloramphenicol. This enzyme is usually encoded on a plasmid and can be transferred along with genes conferring resistance to a number of other antibiotics. Whole genome analysis data showed the presence of a cat gene in the genome of Bartonella.
