Environmental interactions

Question 1

Amoeba life cycle

Answer 1

Trophozoite is metabolically active. Feeds on bacteria and multiplies by binary fission. Chases bacteria
Cysts (endo/ectocyst) provides resistance to adverse conditions
Excyst when environmental conditions are favourable

Question 2

Legionella

Answer 2

Flagellated gamma-proteobacteria.
Non-sporulating, gram negative rod
Causes Legionnaire’s disease
Pneumophila, longbeachae and micdadei are most pathogenic genera

Question 3

Legionella pneumophila

Answer 3

Inhalation of infected aerosols (no person to person transfer)
Pontiac fever in health people, legionnaire’s disease in older and immunocompromised
Reservoir is water (lakes, rivers, showers, taps)
Free living or within amoebae
Associated with 91% of cases

Question 4

Intracellular L. pneumophila

Answer 4

Dual host system. Can grow in amoeba or human macrophages (lung)
Manipulates host vesicular trafficking pathways and establishes a membrane-bound replication vacuole.
Allows evasion of environmental predators, immune responses and access to nutrients

Question 5

L. pneumophila growth phases

Answer 5

Replicative phase. Sodium resistance, non-flagellated, low cytotoxicity
Infectious phase. Short, thick, flagellated and high cytotoxicity.

Ability to prevent phagosome-lysosome fusion is key to virulence

Question 6

L. pneumophila genome

Answer 6

Large number of genes encoding proteins
High similarity to eukaryotic proteins
May have acquired mechanisms of cross-talk with host

Question 7

L. pneumophila life cycle

Answer 7

Free swimming transmissive (engulfed and establish protective vacuoles)
Repress transmission traits and promote replication traits when nutrients are favourable
When conditions deteriorate, express traits that promote survival and transmission (new host)
Develop into mature intracellular form (highly resilient and infectious)
Host lysed and microbe released
Establish biofilm in water if do not encounter host
(biocidal resistance)

Question 8

L. pneumophila in the macrophage

Answer 8

Normally, phagosome with bacterium is trafficked along endosomal route and matures into a lysosome
L. pneumophila escapes with pathway with effector proteins (released via Dot/Icm type IV secretion system)
Legionella-containing vacuole (LCV) transformed into ribosome-studded compartment that mimic RER

Question 9

Alarmone

Answer 9

ppGpp
Stringent response in bacteria
Inhibition of RNA synthesis when there is a shortage of amino acids present

Question 10

ppGpp synthases

Answer 10

ReIA (detects amino acid starvation) and SpoT (disturbances in fatty acid synthesis)
ppGpp accumulates in bacteria
Production of alternative sigma factor RpoS
RpoS regulates quorum sensing systems (CpxRA, PmrAB) which control metabolism, replication and motility