BIOL334- Lecture 3- Legionella and Pathogen survival Flashcards
What factors in the soil and water affect pathogen survival
- Moisture
- Surface/ injected
- High/low organic matter- how much carbon is there? Is it carbon starved?
- Temperature
- UV- a lot of bacteria are damaged by UV
- Predators
- pH
- Salinity levels
(lots of abiotic and biotic factors)
Bacterial pathogen survival times (dry inanimate surfaces)
Campylobacter jejuni: causes food poisoning- 6 days
E.coli: causes gastroenteritis- 1.5 hours to 16 months
Vibrio cholera- cholera- 1-7 days
Viral survival time (dry inanimate surfaces)
Adenovirus- common cold, pneumonia, bronchitis- 7 days-3 months
Coronavirus- SARS, common cold- 3 hours
HIV- AIDS- 7 days +
Rotavirus- vomiting, watery diahorrea, fever- 6-60 days
Survival of pathogens in water
E.coli (8 degrees)- 91 days
Campylobacter (9 degrees)- 4-28 days
Mycobacterium avium paratuberculosis > 3years
Survival of E.coli O157:H7 in manure
Non aerated ovine (sheep) manure- >1 year
Aerated ovine manure- 4 months
Aerated bovine (cattle) manure- 47 days
Cattle/bovine manure at 20 degrees- 100 days
Ovine manure at 4/10 degrees- 100 days
Survival of pathogens in soil
E.coli (25 degrees- 56 days, 6.5-19 degrees- 99 days)
- Lower temp increases survival rate
Salmonella sp (22 degrees- 42 days, 5 degrees 63 days),
What is the impact of amoebae resistant bacteria?
Some microorganisms have evolved to become resistant to amoeba so can exit free living amoeba after internalisation, undamaged.
Legionella pneumophilia though to gain virulence factors whilst living intracellular in the amoeba host.
Two stages in the amoeba life cycle
Trophozoite:
-Metabolically active stage, feeds on bacteria and multiplies by binary fission
Cyst:
- Has two layers (ecto and endocyst), mesocyst present in some species
- Cyst provides resistance to adverse conditions (disinfection, pH, osmotic pressure, temperature)
- Stressed amoeba form cysts
Name a common amoeba host
Acanthamoeba
List some bacteria that are associated with Acanthamobeba
Legionella pneumophilia
E.coli
Mycobacterium tuberculosis
What does the bacterium Legionella pneumophilia cause?
Legionnaires disease- serious type of pneumonia (lung infection).
Pontiac fever- Mild flu-like illness caused by legionella bacteria. Symptoms can include fever, headaches and muscle aches. No pneumonia
Barrow in Furness Legionella case tudy
- 7 fatalities, 180 ill
- From a leisure centre with a hot tub on show
How many species are within the genus Legionella?
57
Mortality rate of Legionella
10-20% (50% in nosocomial infections)
Main source of Legionella
Aquatic reservoir
- Natural environments: lakes, rivers
- Artificial environments: showers, AC, taps, cooling towers
Why is Legionella a new pathogen?
- Ubiquitous in environment but never previously described (stained poorly for visualisation)
- It is a nutritionally demanding pathogen so not isolated on common microbiological media- needs irons salts and cysteine.
- Found to invade protozoans as well as humans
- Originally found in an ‘unsuitable’ environment- AC units
How many serogroups within Legionella pneumophilia? And which is the most virulent to humans?
- 15 serotypes
- sg1 seems to be most virulent to humans (88% of Legionellosis- Pontiac fever and Legionnaires disease caused by sg1).
Top destinations reported for Legionaries Disease
Sri Lanka
Thailand
UAE
Greece
How does Legionella pneumophilia cause infection?
- Inhalation of bacteria from water/soil
- manipulates host cell vesicular trafficking pathways and establishes a membrane bound vacuole
Major virulence factors in Legionella species
- Adhesins: Type 4 pilli
- Endotoxin (LPS)
- Iron uptake
- Motility (flagella)
- Enzymes (Mip)
- Nutrient acquisiton
- Regulatory genes
- Secretion systems
- Toxins (RtxA)
- Stress proteins
What advantages does Legionella pneumophilia have, as an intracellular parasite, compared to other microorganisms?
- Nutrient acquisition through vacuolar membrane
- Evasion of predators in the environment
- Evasion of host immune system
Two phases of growth (once in the vacuole) of Legionella pneumophilia
- Replicative phase: sodium resistance (there is hight Na+ in our bodies), non-flagellated, low cytotoxicity so it can grow.
- Infectious stage: short, thick, flagellated and high toxicity.
What is the key to L.pneumophilia virulence?
- Ability to resist/ prevent phagosome-lysosome fusion
Life cycle of L.pneumophilia
- Free Swimming Transmissive phase:
- Legionella that are engulfed by phagocytic cells establish vacuoles that provide protection against lysosomal digestion.
- When nutrients and other conditions are favourable the Legionella bacteria repress transmission traits and activate pathways that promote replication (low cytotoxicity). - Conditions in the lysosomal compartment deteriorate so the progeny stop dividing and co-ordinately express traits that promote survival in the environment and transmission to a new host.
- After a prolonged period the microbes may continue to develop into a MIF (mature intracellular form) a cell type that is highly infectious and resilient.
- The phagocyte host is lysed due to excessive growth and the microbes are released into the aquatic environment (they express transmissive traits).
- L.pneumophilia that do not immediately encounter a new phagocyte probably establish biofilms in water systems/ponds where they are resistant to biocidal agents.
- When planktonic microbes enter a new phagocyte the cycle begins anew.
