Legionella
LEGIONELLA
Morphology
- Gram negative
- Coccobacilli
- Non capsulated
- Motile by polar or subpolar flagella.
Culture
- Strict aerobe
- Has fastidious requirements and grow on complex media such as buffered charcol, yeast extract (BCYE) agar.
Transmission
- The nature habitats for L. pneumophila are aquatic bodies, including lakes and streams.
- The legionellae survive and multiply inside freeliving amebae and other protozoa.
Mode of transmissions :
1. Aerosolization
- Inhalation of aerosols produced by cooling towers, air conditioners and shower heads which act as disseminators.
2. Aspiration
- Predominant mode of transmission
3. Direct instillation in to the lung
Source
- Water
- No animal reservoir exists
- No carrier state is estabilished
- Man to man transmission does not occur.
Serotypes
- At least 14 serogroups of L. pneumophila have been identified.
- L. pneumophila serogroup 1 (SG 1) accounts nearly all severe infections.
- L. pneumophila serogroup 6 is more commonly involved in hospital – acquired legionnaire’s disease.
Predisposing factors
- Cigarette smoking, lung disease, or alcoholism
- Depressed cell-mediated immunity
Pathogenesis of legionella infection
- Enters the lungs through aspiration or direct inhalation.
- Attachment to host cells is mediated by bacterial type IV pili, heat-shock proteins, and the major outer-membrane protein.
- Cell-mediated immunity is the primary mechanism of host defense against Legionella
- Alveolar macrophages readily phagocytose Legionella.
- The attachment of the bacteria to phagocytes is mediated via Fc receptors and complement receptors, which attach to the bacterial major outer-membrane protein.
- Binding to these receptors promotes phagocytosis but fails to trigger an oxidative burst.
C/F s
- Legionnaire disease is an acute, severe pneumonia that is frequently fatal in immunocompromised patients.
- Pontiac fever is a mild, flu like illness that spares the lungs and is characterized by fever, headache, myalgia, and arthralgia
Diagnosis
- Legionella is grown on complex media such as Buffered Charcoal Yeast Extract agar (BCYE) with alpha ketoglutarate at pH 6.9, temp 35°C and 90% humidity.
- The definitive method for diagnosis of legionella is isolation of the organism from respiratory secretions and specimens.
Treatment
Pontiac fever
- Requires only symptom – based treatment, not antimicrobial therapy.
Legionnaire’s disease
- Azithromycin are DOCs
- Quinolones
- Levofloxacin Gemifloxacin Moxifloxacin
- Alternatives Tetracyclines, Co-trimoxazole, Rifampin (in combination with macrolide or quinolone).
- For transplant recipients quinolones are prefered.
Prevention
- Minimizing production of aerosols in public places from water that may be contaminated with Legionella.
- The bacteria have been isolated from hot water tanks held at over 50°C.
- Methods for decontaminating water systems are still under evaluation.
- Some outbreaks have been aborted by hyperchlorination, by correcting malfunctions in water systems, or by temporarily elevating the system temperature above 70°C.
- The installation of silver and copper ionization systems similar to those used in large swimming pools has been effective as a last resort in hospitals plagued with recurrent nosocomial legionellosis.
Exam Important
LEGIONELLA
Morphology
- Gram negative
Culture
- Has fastidious requirements and grow on complex media such as buffered charcol, yeast extract (BCYE) agar.
Mode of transmissions :
1. Aerosolization
- Inhalation of aerosols produced by cooling towers, air conditioners and shower heads which act as disseminators.
2. Aspiration
- Predominant mode of transmission
3. Direct instillation in to the lung
Source
- Water
Serotypes
- L. pneumophila serogroup 1 (SG 1) accounts nearly all severe infections.
Predisposing factors
- Depressed cell-mediated immunity
Pathogenesis of legionella infection
- Cell-mediated immunity is the primary mechanism of host defense against Legionella
- Alveolar macrophages readily phagocytose Legionella.
- The attachment of the bacteria to phagocytes is mediated via Fc receptors and complement receptors, which attach to the bacterial major outer-membrane protein.
- Binding to these receptors promotes phagocytosis but fails to trigger an oxidative burst.
C/F s
- Legionnaire disease
- Pontiac fever
Diagnosis
- Legionella is grown on complex media such as Buffered Charcoal Yeast Extract agar (BCYE) with alpha ketoglutarate at pH 6.9, temp 35°C and 90% humidity..
Treatment
Legionnaire’s disease
- Azithromycin are DOCs
Prevention
- Some outbreaks have been aborted by hyperchlorination, by correcting malfunctions in water systems, or by temporarily elevating the system temperature above 70°C.
- The installation of silver and copper ionization systems similar to those used in large swimming pools has been effective as a last resort in hospitals plagued with recurrent nosocomial legionellosis.
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