Chapter 138. Moraxella Infections (Part 1) Harrison's Internal Medicine Chapter 138. Moraxella

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Harrison's Internal Medicine Chapter 138. Moraxella Infections Moraxella catarrhalis 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 kidney-bean configuration of Neisseria (Fig. 138-1). These cocci tend to retain crystal violet during the decolorizing step and may be confused...

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Chapter 138. Moraxella Infections (Part 1) Harrison's Internal Medicine > Chapter 138. Moraxella Infections Moraxella catarrhalis 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 kidney-bean 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 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 (e.g., 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 naturally present antibody and complement. Bactericidal antibody emerges after natural infection and may be directed against one or more conserved outer-membrane proteins—a property of potential value in vaccine development. The presence of certain outer-membrane proteins is associated with virulence in mice, and antibody to these proteins may be protective. Antibody to lipooligosaccharide may also provide some degree of protection. These and other bacterial constituents are under investigation for use as vaccines. Epidemiology With repeated cultures and the use of selective media, M. catarrhalis can be isolated from the upper respiratory tract or saliva of >50% of healthy children and 3–7% of healthy adults. When conventional microbiologic techniques are used, Moraxella can be isolated from sputum of ~10% of persons who have chronic bronchitis and ~25% of those who have bronchiectasis in the absence of acute infection. Investigators in both the northern and southern hemispheres have
reported a striking seasonal variation in the isolation of this organism from clinical specimens, with a peak in late winter/early spring and a nadir in late summer/early fall. Direct contact has not been shown to contribute to community-acquired infection, but nosocomial spread of infection has been documented occasionally. Clinical Manifestations Otitis Media and Sinusitis M. catarrhalis is the third most common bacterial isolate from middle-ear fluid of children with otitis media, being surpassed only by Streptococcus pneumoniae and nontypable Haemophilus influenzae. This organism is also a prominent isolate from sinus cavities in acute and chronic sinusitis. Purulent Tracheobronchitis and Pneumonia M. catarrhalis causes acute exacerbations of chronic bronchitis (increased production and/or purulence of sputum, which may be accompanied by fever and leukocytosis) and pneumonia. Acquisition of a new bacterial strain is often responsible. The great majority of infected persons are >50 years old and have a long history of cigarette smoking and underlying chronic obstructive pulmonary disease (COPD); many have lung cancer as well. In one study, 76% of affected persons had COPD (severe in many cases), and one-third of those with COPD had lung cancer; most patients also had clinical evidence of malnutrition. In one
extensive series of cases, M. catarrhalis pneumonia did not occur in otherwise- healthy hosts. Recent prospective studies implicate this organism in ~10% of exacerbations of chronic bronchitis. Symptoms of M. catarrhalis infection have been regarded as modest in severity. Both cough and the amount and purulence of sputum are usually increased above baseline. Chills are reported in one-quarter of patients, pleuritic pain in one-third, and malaise in 40%. Most patients have peak temperatures of