In detail, the potential presence of the chloramphenicol marker is first screened using a real-time PCR method (see Related Methods QL-ELE-cat-F/R). In case a positive real-time PCR signal is obtained, the presence of the full-length chloramphenicol marker is then evaluated by a nested-PCR consisting of the related method QL-ELE-cat-F1/cat-R1 and this method.

For the nested PCR the majority of the chloramphenicol marker sequence is amplified using the primer pair cat-F1/cat-R1 (see Related Methods). A 1:100 dilution of the generated PCR product is then submitted to a second PCR reaction using the primer pair cat-F2/cat-R2 (this method) in order to increase the specific amplicon yield.