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Overview of Legionella: Pathogenicity, Clinical Syndromes, and Control Measures

Legionella, specifically Legionella pneumophila, is a Gram-negative bacterium requiring iron and cysteine for growth. It typically grows in buffered charcoal yeast extract agar (BCYE) at optimum temperatures of 35-36°C with a CO2 concentration of 2.5-5%. The most notable diseases caused by Legionella include Legionnaires’ Disease and Pontiac Fever, presenting with varying severity. Precise laboratory diagnosis involves culture on BCYE medium and antigen tests. Effective treatment options include high-dose Erythromycin and Rifampicin. Control strategies focus on eliminating bacteria from potential aerosol-generating water sources.

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Overview of Legionella: Pathogenicity, Clinical Syndromes, and Control Measures

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  1. بسم الله الرحمن الرحيم GENUS: LEGIONELLA Prof. Khalifa Sifaw Ghenghesh

  2. Gram-negative rods • Requires iron and cysteine for growth • Buffered charcoal yeast-extract agar (BCYE) • Optimum growth temp. >> 35-36oC • Grow better >> 2.5-5% CO2 • 39 species • Legionella pneumophila

  3. Legionella pneumophila • Divided into 3 subspecies • L. pneumophila ssp. pneumophila • L. pneumophila ssp. fraseri • L. pneumophila ssp. pascullei • L. pneumophila divided to >14 serogroups • Most infections caused by: • L. pneumophila, serogroup 1 (SG1)

  4. Legionella pneumophila (TEM)

  5. CLINICAL SYNDROMES 1. Legionnaires’ Disease • Pneumonia • Incubation period >> 2-10 days • High fever, respiratory distress, cough, confusion and local neurological signs. • Mortality • 10% in healthy individuals

  6. 2. Pontiac Fever • A brief febrile influenza-like illness • A high attack rate with no mortality • Source of infection usually is not identified

  7. Impression smear from the lung of a patient fatally infected with L. pneumophila serogroup 1, demonstrating many thin, Gram-negative bacilli (arrows).

  8. Lung cross-section of patient with L. pneumophila infectionGram-negative, coccoid rods

  9. LABORATORY DIAGNOSIS • SPECIMENS • Sputum, bronchial aspirate or washings • Pleural fluid, lung biopsy or autopsy material >> Microscopy examination • CULTURE • BCYE with or without antibiotics • Incubate for 48 hours at 36oC aerobically with 2.5% CO2 • Plates kept for least 10-14 days before discarded as negative • Colonies >> “cut-glass” appearance by plate microscopy or fluorescing blue-white under UV light • IDENTIFICATION • Specific antisera in an immunofluorescence test.

  10. ANTIGEN TESTS • Urine for legionella antigen by ELISA for identifying L. pneumophila SC1 • SEROLOGY • Not reliable

  11. Charcoal-yeast extract agar plate culture of Legionella pneumophila.

  12. Charcoal-Yeast extract agar plate culture of Legionella pneumophilia - Circular off-white colonies (day 6, at 36oC)

  13. L. pneumophila stained using direct FA technique (400x)

  14. TREATMENT • Erythromycin in high dosage (IV) • Rifampicin, Ciprofloxacin

  15. EPIDEMIOLOGY • Disease occurs in outbreak form due to dissemination of the bacteria in aerosols • Infected aerosols generated from warm water sources: • Ponds of cooling towers of refrigeration plants in air-conditioning systems • Domestic hot water systems in hotels and hospitals • Warm water in nebulizers and oxygen line humidifiers • Whirlpool spa baths and showers

  16. CONTROL • Eradication of Legionella organisms in various kinds of water sources that may give rise to aerosol production. • Eradication by • Heat or disinfection with chlorine or other biocides • Hot water should be above 60oC before distribution

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