Rapid identification of Mycobacterium xenopi from bacterial colonies or "Bactec" culture by the polymerase chain reaction and a luminescent sandwich hybridization assay.

Oligonucleotide primers were used in the polymerase chain reaction (PCR) to amplify a specific 584-bp DNA fragment, located in the 16S RNA gene of Mycobacterium xenopi. This set of primers, X222 and X224, was able to discriminate between the pathogen and other mycobacterial species as well as non-mycobacterial strains; it detected down to 3 fg of M. xenopi DNA, i.e. about one genome equivalent. These oligonucleotide primers proved suitable for the routine identification of M. xenopi cultures, starting from one single colony on solid medium or from a liquid culture in Middelbrook 12B "Bactec" medium. In addition, a luminescent hybridization assay was designed for use on PCR-amplified DNA. This system, which, for capture, relied on a matrix-bound oligonucleotide (M30) specific for the genus Mycobacterium and, for detection, on a biotinylated xenopi-specific X221 probe, proved fully specific, highly sensitive and rapid for the evaluation of M. xenopi Bactec cultures at low growth index.