Legionella pneumophilia - MegaMicro

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Legionella pneumophilia

Micro > Bacteriology > Gram-negative bacteria
Legionella pneumophila

1. Structure
a. Gram-negative
b. Bacilli
c. Non-encapsulated
d. Single, polar flagellum

2. Pathobiology:
a. Aerobic
b. Spread primarily through aerosolized water droplets
i. Can also be transmitted via aspirating water containing bacteria, or after using contaminated potting soil
c. Life cycle consists of 2 phases: replicative phase, infectious phase
i. Replicative: non-motile bacteria with low or nonexistent toxicity
ii. Infectious: growth of flagella allows for motility; more toxic
d. Main hosts are amoeba and human macrophages
i. Bacterium begins infection by being phagocytosed by macrophages. Vacuole forms and protects bacterium; prevents delivery to lysosome in replicative phase
ii. Replicate
1. Transformation to infectious phase --> growth of flagella, lysosome avoidance factors, surface modifications
iii. Newly replicated bacteria move into transmissive phase once host nutrients are depleted, lyse host macrophage, and restart infection process

3. Epidemiology
a. Largely aquatic, inhabit non-marine water sources
b. May inhabit man-made water distribution systems
i. Hot tubs, cooling towers, fountains, swimming pools, water systems in hotels and hospitals

4. Laboratory diagnosis
a. Culture
i. Can detect all species and serogroups, but technically difficult and slow to culture
ii. Requires BCYE agar (buffered charcoal yeast extract)
b. Urinary antigen test
i. Most commonly used lab test for diagnosis
ii. Detects a part of the bacterium in urine
iii. Only detects L. pneumophilia type I
c. Paired serology
i. requires acute and convalescent serologies
ii. not useful for acute diseae - for epidemiologic purposes only
d. DFA stain
      i. only valid for Legionella pneumophilia type I
e. PCR

5. Disease manifestations
a. Legionnaires’ Disease
i. Similar to other types of pneumonia
      1. lobar or multilobar consolidation
ii. Symptoms: cough (may produce blood-streaked sputum), shortness of breath, fever, muscle aches, headaches, chills
1. Can also be associated with diarrhea, nausea and confusion
2. Begin 2-10 days after exposure to the bacteria, but can also take longer

b. Pontiac fever
i. Less serious infection than Legionnaires’
ii. Different than Legionnaires’ because someone with Pontiac fever does not have pneumonia
iii. Flu-like symptoms
iv. Mechanism of disease is inhalatin of bacterial antigens and endotoxin from infected aerosols (eg. air conditioning units), leading to symptoms. Disease is not due to infection / invastion of the organism in tissue.

d. Therapy, Prevention, Control
i. Can be treated with antibiotics
1. resistant to penicillins and cephalosporins
2. Treated only with antibiotics that can enter host cells, like macrolides (azithromycin), quinolones (ciprofloxacin, levofloxacin), tetracycline, doxycycline
ii. Pontiac fever goes away on its own
     1. Remove exposure through treatment of air handling systems

e. Prevention and control
i. Minimize bacteria growth in buildings’ water systems and devices (hot tubs, fountains, cooling towards) to prevent infection

Key Words:
1.       Legionnaires’ Disease
2.       Pontiac fever
3.       Macrolides
4.       Quinolones
5.       Public water systems
 
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