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

Abstract 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.