tailieunhanh - Chapter 138. The gram-negative coccus

Moraxella catarrhalis is a component of the normal bacterial flora of the upper airways and has been increasingly recognized as a cause of otitis media, sinusitis, and bronchopulmonary infection. Over the past several decades, this organism has been variously designated as Micrococcus catarrhalis, Neisseria catarrhalis, and Branhamella catarrhalis. Bacteriology and Immunity On Gram's staining, M. catarrhalis organisms appear as gram-negative cocci, sometimes occurring in pairs and having the side-by-side kidneybean configuration of Neisseria (Fig. 138-1). These cocci tend to retain crystal violet during the decolorizing step and may be confused with Staphylococcus aureus. Moraxella colonies grow well on blood. | Chapter 138. The gram-negative coccus Moraxella catarrhalis is a component of the normal bacterial flora of the upper airways and has been increasingly recognized as a cause of otitis media sinusitis and bronchopulmonary infection. Over the past several decades this organism has been variously designated as Micrococcus catarrhalis Neisseria catarrhalis and Branhamella catarrhalis. Bacteriology and Immunity On Gram s staining M. catarrhalis organisms appear as gram-negative cocci sometimes occurring in pairs and having the side-by-side kidneybean configuration of Neisseria Fig. 138-1 . These cocci tend to retain crystal violet during the decolorizing step and may be confused with Staphylococcus aureus. Moraxella colonies grow well on blood or chocolate agar but may be overlooked because of their resemblance to the Neisseria spp. that are major components of the normal pharyngeal flora. Moraxella is readily distinguishable from Neisseria spp. by biochemical tests. Figure 138-1 Source Fauci AS Kasper DL Braunwald E Hauser SL Longo DL Jameson JL. Loscalzo J Hãrrisữ í s Principỉes c ỉnternãị M Jicirie. 17th Edition http Copyright @ The McGraw-Hill Companies Inc. All rights reserved. Gram-stained sputum from a patient with acute purulent tracheobronchitis. Many polymorphonuclear neutrophils and a few macrophages are seen along with many gram-negative cocci Moraxella catarrhalis a few of which appear as pairs. Nearly all organisms are cell associated and probably have been taken up by phagocytes consistent with the notion that Moraxella is a lower-grade pathogen than organisms that are found extracellularly in sputum specimens . Streptococcus pneumoniae . Strains of M. catarrhalis show a surprising degree of homogeneity in terms of their outer-membrane proteins. Antibody to some of these proteins is generally present in serum of children 4 years old however colonizing or disease-causing isolates may survive in serum despite this .