Causative Agent

The causative agent of Legionnaires' disease is Legionella pneumophila (figure 23.20), a member of the y-proteobacteria. The organism is rod-shaped, Gram-negative, and requires a special medium for laboratory culture, which partly explains why it escaped detection for so long. Also, in tissue, L. pneumophila stains poorly with many of the usual microbiological stains. There are a number of different strains of L. pneumophila, some of which cause symptoms differing from Legionnaires' disease.

Table 23.9 Tuberculosis

© Airborne Mycobacterium tuberculosis bacteria are inhaled and lodge in the lungs

<2 The bacteria are phagocytized by lung macrophages and multiply within them, protected by lipid-containing cell walls

© Infected macrophages are carried to various parts of the body such as the kidneys, brain, lungs, and lymph nodes; release of M. tuberculosis occurs

@ Delayed hypersensitivity develops; wherever infected M. tuberculosis has lodged, an intense inflammatory reaction develops

© The bacteria are surrounded by macrophages and lymphocytes; growth of the bacteria ceases

© Intense inflammatory reaction and release of enzymes can cause caseation necrosis and cavity formation

@ With uncontrolled or reactive infection, M. tuberculosis exits the body through the mouth with coughing or singing

Symptoms Chronic fever, weight loss, cough, sputum production

Incubation period 2 to 10 weeks

Causative agent Mycobacterium tuberculosis; unusual cell wall with high lipid content

Pathogenesis Colonization of the alveoli incites inflammatory response; ingestion by macrophages follows; organisms survive ingestion and are carried to lymph nodes, lungs, and other body tissues; tubercle bacilli multiply; granulomas form

Epidemiology Inhalation of airborne organisms; latent infections can reactivate

Prevention and BCG vaccination, not used in the United treatment States; tuberculin (Mantoux) test for detection of infection, allows early therapy of cases; treatment of young people with positive tests and individuals whose skin test converts from negative to positive.Treatment: two or more antitubercular medications given simultaneously, such as isoniazid (INH) and rifampin

Nester-Anderson-Roberts: I IV. Infectious Diseases I 23. Respiratory System I I © The McGraw-Hill

Microbiology, A Human Infections Companies, 2003

Perspective, Fourth Edition

10 mm

Figure 23.20 Legionella pneumophila Stained with Fluorescent Antibody When present in tissue or sputum, the bacterium fails to stain with most of the usual microbiological stains.

23.5 Bacterial Infections of the Lower Respiratory System 585

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