Legionella and Pseudomonas Flashcards
environmental niches and routes of exposure are typical for Legionella
Environmental Niches -most commonly spread through aerosols -replicates anywhere between 5 to 63 C -often correlated with the presence of free-living amebas in natural water sources -loves biofilms Routes of Exposure -air-conditioning cooling towers -whirlpool spas -sink taps and shower heads
environmental niches and routes of exposure are typical for Pseudomonas
Environmental niches
-“Water Bugs” found is soil and water
-Ubiquitous in environment
-Abundant on fresh fruits and vegetables
Routes of exposure
-Frequent contaminants of whirlpools, sinks, respiratory therapy equipment
-Very prevalent in hospital setting due to patient susceptibility and antibiotic selection
Compare the intracellular life styles of Legionella in nature and in the host.
Nature:
-“Coiling phagocytosis” – special mechanism of uptake of Legionella in macrophages AND amebas
-Legionella lives intracellularly in amebas in a fashion analogous to its life in macrophages in the human host!!
In human Hosts:
-Legionella is a facultative intracellular pathogen that survives in macrophages
-Coiling phagocytosis brings it into phagosome- doesn’t acidify or fuse w/ lysosome
-Phagosome surrounded by ribosome studded ER
-Legionella multiplies in the phagosome
-Phagosome ruptures and releases bacteria
-Cell lyses and releases bacteria out
Indicate patient factors predisposing individuals to infections with Legionella:
- immunosuppression
- cigarette smoking
- renal failure
- age greater than 50 years
- AIDS
- hematologic malignancies
- lung cancer
- males at higher risk than women
- Alcohol abuse a possible factor
Predominant respiratory diseases associated with Legionella
Legionellosis -first recognized in 1976 -fever, chills, headache -severe pneumonia -nausea, vomiting, GI symptoms -overall mortality rate 15-30% -attack rate (# who become ill of those exposed) 5% Pontiac Fever -Pontiac, MI Health Dept outbreak 1968 -influenza-like -fever, chills, myalgia, headache -no evidence of pneumonia -self-limiting -no agent cultured (serum samples saved) -retrospectively determined to also be Legionella
key laboratory characteristics of Legionella
- Gram-negative slender bacilli
- BUT they do not take up the Gram stain well:
- hard to see in clinical samples
- Fluorescence staining on specimens (or after growth on cultures) or Dieterle’s Silver Stain used instead of Gram Stain
- Growth requirements include amino acids, iron and other trace metals –
- Special media required: Buffered Charcoal Yeast Extract agar.
- Slow growing 4 days to a week
environmental niches and routes of exposure are typical for Pseudomonas.
Environmental niches
-“Water Bugs” found is soil and water
-Ubiquitous in environment
-Abundant on fresh fruits and vegetables
Routes of exposure
-Frequent contaminants of whirlpools, sinks, respiratory therapy equipment
-Very prevalent in hospital setting due to patient susceptibility and antibiotic selection
patient factors predispose individuals to infections with Pseudomonas
pneumonia in cystic fibrosis patients burn infections hospital acquired infections Catheters Any other break in barrier Neutropenia diabetes Prematurity
predominant respiratory diseases associated with pseudomonas
Most recognized Ps.aeruginosa diseases pneumonia in cystic fibrosis patients burn infections hospital acquired infections cellulitis folliculitis urinary tract infection swimmer’s ear Will attack almost any system
role of biofilms in disease and resistance to antimicrobial infections
- P. aeruginosa and other agents (Burkholderia cepacia) form biofilm
- Bacteria are surrounded with breakdown products of bacteria and immune cells
- Matrix makes bacteria more resistant to both antibiotics and the immune system
- Less susceptible to antibiotics in biofilm!
key laboratory characteristics and methods for identifying Pseudomonas.
- Growth on MacConkey (Lac -)
- Oxidase-positive
- Pigment production Pyocyanin
- Glucose oxidation (failure to oxidize other common carbohydrates)
- Characteristic smell! Artificial grape-like odor
