A note on hydrolysis of tributyrin by Branhamella and Neisseria

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.

Branhamella catarrhalis: an organism gaining respect as a pathogen

Branhamella catarrhalis was formerly regarded as a common, essentially harmless inhabitant of the pharynx. This misapprehension was caused, in part, by confusion with another pharyngeal resident, Neisseria cinerea. The two organisms can now be differentiated by the positive reactions of B. catarrhalis in tests for nitrate reduction and hydrolysis of tributyrin and DNase. B. catarrhalis is currently recognized as the third most frequent cause of acute otitis media and acute sinusitis in young children. It often causes acute exacerbations of chronic bronchopulmonary disease in older or immunocompromised adults and is incriminated occasionally in meningitis, endocarditis, bacteremia, conjunctivitis, keratitis, and urogenital infections. Virulence-associated factors, such as pili, capsules, outer membrane vesicles, iron acquisition proteins, histamine-synthesizing ability, resistance to the bactericidal action of normal human serum, and binding to the C1q complement component, have been identified in some strains. beta-Lactamase producing strains, first detected in 1976, have risen to approximately 75% worldwide. Thus far, however, practically all American strains of B. catarrhalis remain susceptible to alternative antibiotics. A possible selective advantage of recent isolates is their reportedly heightened tendency for adherence to oropharyngeal cells from patients with chronic bronchopulmonary disease.

Branhamella catarrhalis: phenotypic characteristics

PURPOSE

This review provides a comprehensive description and discussion of recognized phenotypic characteristics of Branhamella catarrhalis. An emphasis is placed on attributes of this organism that are relevant to its recovery and identification in the clinical microbiology laboratory. In addition, characteristics useful in determining strain identity for use in epidemiologic investigations are addressed. Finally, factors are discussed that may account for the infection-causing potential of B. catarrhalis or at least are of potential consequence to investigations of the pathogenesis of Branhamella disease.

CONCLUSIONS

B. catarrhalis is readily isolated from human clinical specimens and can be easily identified using simple, rapid laboratory techniques. Restriction endonuclease analysis of chromosomal deoxyribonucleic acid has proven to be a useful tool in epidemiologic studies. Beta-lactamase isoelectric focusing is of limited value because of the small number of distinct patterns. The lipopolysaccharide and outer membrane proteins of B. catarrhalis have been characterized and found to be relatively non-varying among different strains. Circumstantial evidence exists in support of the hypothesis that the B. catarrhalis beta-lactamase is a virulence determinant.