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BIOL334 > BIOL334- Lecture 3- Legionella and Pathogen survival > Flashcards

BIOL334- Lecture 3- Legionella and Pathogen survival Flashcards

1
Q

What factors in the soil and water affect pathogen survival

A
  • 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)

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2
Q

Bacterial pathogen survival times (dry inanimate surfaces)

A

Campylobacter jejuni: causes food poisoning- 6 days
E.coli: causes gastroenteritis- 1.5 hours to 16 months
Vibrio cholera- cholera- 1-7 days

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3
Q

Viral survival time (dry inanimate surfaces)

A

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

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4
Q

Survival of pathogens in water

A

E.coli (8 degrees)- 91 days
Campylobacter (9 degrees)- 4-28 days
Mycobacterium avium paratuberculosis > 3years

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5
Q

Survival of E.coli O157:H7 in manure

A

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

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6
Q

Survival of pathogens in soil

A

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),

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7
Q

What is the impact of amoebae resistant bacteria?

A

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.

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8
Q

Two stages in the amoeba life cycle

A

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
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9
Q

Name a common amoeba host

A

Acanthamoeba

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10
Q

List some bacteria that are associated with Acanthamobeba

A

Legionella pneumophilia
E.coli
Mycobacterium tuberculosis

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11
Q

What does the bacterium Legionella pneumophilia cause?

A

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

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12
Q

Barrow in Furness Legionella case tudy

A
  • 7 fatalities, 180 ill

- From a leisure centre with a hot tub on show

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13
Q

How many species are within the genus Legionella?

A

57

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14
Q

Mortality rate of Legionella

A

10-20% (50% in nosocomial infections)

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15
Q

Main source of Legionella

A

Aquatic reservoir

  • Natural environments: lakes, rivers
  • Artificial environments: showers, AC, taps, cooling towers
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16
Q

Why is Legionella a new pathogen?

A
  • 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
17
Q

How many serogroups within Legionella pneumophilia? And which is the most virulent to humans?

A
  • 15 serotypes

- sg1 seems to be most virulent to humans (88% of Legionellosis- Pontiac fever and Legionnaires disease caused by sg1).

18
Q

Top destinations reported for Legionaries Disease

A

Sri Lanka
Thailand
UAE
Greece

19
Q

How does Legionella pneumophilia cause infection?

A
  • Inhalation of bacteria from water/soil

- manipulates host cell vesicular trafficking pathways and establishes a membrane bound vacuole

20
Q

Major virulence factors in Legionella species

A
  • Adhesins: Type 4 pilli
  • Endotoxin (LPS)
  • Iron uptake
  • Motility (flagella)
  • Enzymes (Mip)
  • Nutrient acquisiton
  • Regulatory genes
  • Secretion systems
  • Toxins (RtxA)
  • Stress proteins
21
Q

What advantages does Legionella pneumophilia have, as an intracellular parasite, compared to other microorganisms?

A
  • Nutrient acquisition through vacuolar membrane
  • Evasion of predators in the environment
  • Evasion of host immune system
22
Q

Two phases of growth (once in the vacuole) of Legionella pneumophilia

A
  1. Replicative phase: sodium resistance (there is hight Na+ in our bodies), non-flagellated, low cytotoxicity so it can grow.
  2. Infectious stage: short, thick, flagellated and high toxicity.
23
Q

What is the key to L.pneumophilia virulence?

A
  • Ability to resist/ prevent phagosome-lysosome fusion
24
Q

Life cycle of L.pneumophilia

A
  1. 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).
  2. 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.
  3. 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.
  4. The phagocyte host is lysed due to excessive growth and the microbes are released into the aquatic environment (they express transmissive traits).
  5. L.pneumophilia that do not immediately encounter a new phagocyte probably establish biofilms in water systems/ponds where they are resistant to biocidal agents.
  6. When planktonic microbes enter a new phagocyte the cycle begins anew.
25
Q

Formation of the replicative vacuole: Legionella pneumophilia

A
  1. After uptake into the target amoeba or macrophage the Legionella containing vacuole (LCV) evades transport to the lysosomal network.
  2. Within minutes of uptake vesicles derived from ER and mitochondria appear in close proximity to LCV surface. The Dot/Icm T4 SS delivers effector proteins that protect the LCV and recruit the vesicles and mitochondria- stopping lysosomal fusion
  3. The identity of the ER-derived vesicles is based on the presence of proteins that are known to be associated with the early secretory apparatus
  4. The vesicles that surround the LCV appear to be docked and extend out to the surface and eventually the membranes that surround the bacterium become similar to rough ER in appearance and become studded with ribosomes.
  5. Within this ER like compartment the bacterium replicates to high numbers and eventually lyses the host cell. The ER like compartment mimics the host cell and therefore evades lysosomes.
26
Q

What happens in terms of the vacuole for non pathogens (that Legionella avoids)

A

Normally, the membrane bound compartment acquires early and late endoscopes (membrane bound vesicles) before entering the lysosomal network.
- Dot/Ic, defect in organelle trafficking.

27
Q

Which receptor mediates attachment of Legionella pneumophilia to amoeba

A

Gal/Gal NAc receptor

28
Q

What is ppGpp?

A

An alarm that is involved in the stress response in L.pneumophilia bacteria (stress response to amino acid depletion), causing inhibition of RNA synthesis when aa’s are not present.

29
Q

What does RelA do?

A

RelA detects amino acid starvation

30
Q

What does SpoT do?

A

Monitors imbalances/ disturbances in fatty acid synthesis

31
Q

Describe the role of RelA and SpoT and downstream effectors

A

RelA and SpoT: ppGpp synthases

  • They detect amino acid and fatty acid depletion
  • depletion causes an accumulation of ppGpp
  • ppGpp accumulation leads to production of the alternative sigma factor RpoS.
  • RpoS regulates QS systems which control metabolism, replication, motility and virulence traits.
  • replication is turned off under depleted amino acid states and transmissive traits are turned on.
32
Q

What is the function of the CrsA regulator

A
  • RNA binding global regulator CrsA controls an on/off switch of replicative/ transmission phases in L.pneumophilia
33
Q

Describe why amoeba are described as training grounds for Legionella pneumophilia

A
  • In outbreaks of Legionnaires disease, amoebae and bacteria have been isolated from the same source of infection and the isolated amoebae supported intracellular replication of the pathogen.
  • Following intracellular replication within protozoa L.pneumophilia exhibit a dramatic increase in resistance to adverse conditions and infectivity for mammalian cells.
  • The number of bacteria from the source of infection is low/undetectable- enhanced infectivity compensates for low ID.
  • VBNC L.pneumophilia can be resuscitated by co-culture with amoeba.

BIOL334 (9 decks)

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