Editing Chloramphenicol (section)

===Resistance===

Three mechanisms of [[Antibiotic resistance|resistance]] to chloramphenicol are known: reduced membrane permeability, mutation of the [[50S ribosomal subunit]], and elaboration of chloramphenicol acetyltransferase. It is easy to select for reduced membrane permeability to chloramphenicol ''in vitro'' by serial passage of bacteria, and this is the most common mechanism of low-level chloramphenicol resistance. High-level resistance is conferred by the ''cat''-gene;<ref name="m586">{{cite journal | vauthors = Gil JA, Kieser HM, Hopwood DA | title = Cloning of a chloramphenicol acetyltransferase gene of Streptomyces acrimycini and its expression in Streptomyces and Escherichia coli | journal = Gene | volume = 38 | issue = 1–3 | pages = 1–8 | date = 1985 | pmid = 3905512 | doi = 10.1016/0378-1119(85)90197-0 }}</ref> this [[gene]] codes for an [[enzyme]] called [[chloramphenicol acetyltransferase]], which inactivates chloramphenicol by covalently linking one or two [[acetyl]] groups, derived from acetyl-''S''-coenzyme A, to the [[hydroxyl]] groups on the chloramphenicol molecule. The acetylation prevents chloramphenicol from binding to the ribosome. Resistance-conferring mutations of the 50S ribosomal subunit are rare.{{medical citation needed|date=August 2022}}

Chloramphenicol resistance may be carried on a plasmid that also codes for resistance to other drugs. One example is the [[ACCoT]] plasmid (A=[[ampicillin]], C=chloramphenicol, Co=[[co-trimoxazole]], T=[[tetracycline]]), which mediates [[multiple drug resistance]] in typhoid (also called [[R factors]]).{{medical citation needed|date=August 2022}}

As of 2014 some ''[[Enterococcus faecium]]'' and'' [[Pseudomonas aeruginosa]]'' strains are resistant to chloramphenicol. Some ''[[Veillonella]]'' spp. and ''[[Staphylococcus capitis]]'' strains have also developed resistance to chloramphenicol to varying degrees.<ref>{{cite web |title= Chloramphenicol spectrum of bacterial susceptibility and Resistance |url=http://www.toku-e.com/Upload/Products/PDS/20120618001452.pdf|access-date=15 May 2012|url-status=dead|archive-url=https://web.archive.org/web/20140211211304/http://www.toku-e.com/Upload/Products/PDS/20120618001452.pdf | work = Product Data Safety Sheet | publisher = TOKU-E | date = December 2010 |archive-date=11 February 2014}}</ref>

Some other resistance genes beyond ''cat'' are known, such as chloramphenicol hydrolase,<ref name="b716">{{cite journal | vauthors = Mosher RH, Ranade NP, Schrempf H, Vining LC | title = Chloramphenicol resistance in Streptomyces: cloning and characterization of a chloramphenicol hydrolase gene from Streptomyces venezuelae | journal = Journal of General Microbiology | volume = 136 | issue = 2 | pages = 293–301 | date = February 1990 | pmid = 2324705 | doi = 10.1099/00221287-136-2-293 | doi-access = free }}</ref> and chloramphenicol phosphotransferase.<ref name="u157">{{cite journal | vauthors = Mosher RH, Camp DJ, Yang K, Brown MP, Shaw WV, Vining LC | title = Inactivation of chloramphenicol by O-phosphorylation. A novel resistance mechanism in Streptomyces venezuelae ISP5230, a chloramphenicol producer | journal = The Journal of Biological Chemistry | volume = 270 | issue = 45 | pages = 27000–27006 | date = November 1995 | pmid = 7592948 | doi = 10.1074/jbc.270.45.27000 | doi-access = free }}</ref>