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

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 r

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

<38.3°C (<101°F), and peripheral white blood cell counts are <10,000/µL in nearly one-quarter of cases

Microscopic examination of a high-quality sputum specimen after Gram's staining regularly reveals profuse organisms, and quantitative culture yields ~2 x

108 colony-forming units per milliliter The radiologic appearance is variable; in one study, 43% of subjects had segmental or lobar infiltrates, and the remainder had a mixed pattern of subsegmental, segmental, interstitial, and diffuse involvement These clinical, laboratory, and radiographic findings do not differ

from those of pneumococcal or Haemophilus pneumonia in an older patient population However, a far lesser degree of bloodstream invasion occurs in M

catarrhalis infection; in one series, none of 25 patients with M catarrhalis

pneumonia had bacteremia Nevertheless, pneumonia due to M catarrhalis is a

marker for severe underlying disease: nearly half of patients die within 3 months

of onset