Development of a species-specific DNA probe for Moraxella (Branhamella) catarrhalis

Moraxella (Branhamella) catarrhalis is an aerobic Gram-negative diplococcus that is now recognized as a pathogen of the respiratory tract. Rapid and direct identification of this bacterium has become important to the clinical microbiology laboratory. Recently, rapid tests for the identification of Neisseria species and M. catarrhalis have been commercialized but they are primarily for Neisseriae; in these kits, M. catarrhalis is always identified presumptively. We have developed a DNA probe of chromosomal origin that is 100% specific for M. catarrhalis. The oligonucleotide probe was derived from a cloned Ase I chromosomal DNA fragment of M. catarrhalis that did not react with Haemophilus influenzae DNA in hybridization experiments. Three of the first 17 Ase I clones were selected randomly to be tested by colony hybridization against several different species that colonize the human respiratory tract. One of these three, pLQ121, has a 550 bp fragment inserted into pBR322 and was determined to be 100% specific to M. catarrhalis. This fragment was partially sequenced and a 30-mer oligonucleotide was synthesized from the sequence data. This probe was also shown to be 100% specific to the species.