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
- Legionella 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.
- Because the organisms possess pili that may mediate adherence to respiratory tract epithelial cells, conditions that impair mucociliary clearance, including cigarette smoking, lung disease, or alcoholism, predispose to Legionnaires’ disease.
- Cell-mediated immunity is the primary mechanism of host defense against Legionella.
- Alveolar macrophages readily phagocytose Legionella. T
- 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.
Don’t Forget to Solve all the previous Year Question asked on Legionella
Click Here to Start Quiz
Click Here to Start Quiz
