Addition of the antibiotic chloramphenicol to bacterial culture medium can be used to amplify the copy number of plasmids. Chloramphenicol inhibits bacterial protein synthesis and thus bacteria chromosomal replication. Alex Aitken Page 1 Chloramphenicol - amplification of plasmids Prepared by Ms Alex Aitken When low-copy-number plasmids containing the pMB1 or ColE1 origin of replication are prepared, Cultures of bacteria containing low-copy number plasmids amplified in the presence of chloramphenicol should be treated as if they contain high-copy-number plasmids when choosing the appropriate culture volumes for the QIAGEN-tip to be used. The plasmid I'm trying to purify encodes the CAT gene, so Chloramphenicol isn't possible for this type of approach. If you are experiencing low yields from a plasmid whose copy number is unknown, it is entirely possible that you are working with a low copy plasmid. When increasing the culture volume, be aware that a higher volume of lysate passed over the binding matrix could clog the matrix when performing filter based plasmid prepping. Chloramphenicol is an antibiotic useful for the treatment of a number of bacterial infections. This includes use as an eye ointment to treat conjunctivitis. [4] By mouth or by injection into a vein , it is used to treat meningitis , plague , cholera , and typhoid fever. [3] When low-copy-number plasmids containing the pMB1 or ColE1 origin of replication are prepared using QIAGEN Plasmid Purification Kits, plasmid DNA yields can be improved by adding chloramphenicol to the culture medium (170 mg/liter) to amplify copy numbers. However, it will increase the copy number of your vector several times. Irrespective of the way you amplify your vector using chloramphenicol, treat the resulting culture as containing a high copy number vector. High-copy-number and low-copy-number plasmid vectors for lacZα-complementation and chloramphenicol- or kanamycin-resistance selection If you know you are working with a low-copy number plasmid, you shouldn’t be too surprised with a low yield and you might therefore decide to set up more cultures. On the other hand, if you get a poor yield from a high copy plasmid, then you know you have some troubleshooting to do, assuming your insert is not too large to begin with!.