1.12. Molecular basis for bacterial virulence and survival within infected hosts and environment

Question 1

Pathogenicity:

Answer 1

the ability of an organism to cause diseases

Question 2

Virulence:

Answer 2

degree of pathogenicity
–Case fatality rate
–Ability to invade the host

Question 3

genetic diversity

Answer 3

•Limited number of microbial species
–Cause disease
–Produce products
•However, diversity is reflected in the complexity of 16S rRNAphylogenetic trees
•Whole genomes to discover subpopulations

Question 4

core genome

Answer 4

shared by all members of the bacterial species

Question 5

flexible (accessory/ dispensable) genome

Answer 5

some but not all of the same bacterial species

Question 6

Pseudomonas aeruginosa

Answer 6

Opportunistic pathogen
1.Able to switch between acute and chronic, adapt to environment
»Pathogenicity islands that can be excised and transferred
»Important for management of the disease and preventing transmission

Question 7

Intracellular survival

Answer 7

• Many bacteria have a facultative intracellular lifestyle
• Able to evade the immune system
• Contributes to their respective virulence
• E.g Listeria monocytogenes, Salmonella spp and Mycobacterium tuberculosis

Question 8

Listeria monoctytogenes

Answer 8

•Food borne pathogen•Able to cross 3 biological barriers (intestinal, boodbrain and foeto-placental)
- Once inside the cell these organisms escape from the phagosomeinto the cytoplasm, where it is propelled by actin-based motility forming comet tails

Question 9

Environmental survival

Answer 9

• Some organisms have the ability to survive under stressful situations (e.g. the environment)
• Sporeforming bacteria e.g. Clostridium difficile and non-enveloped viruses e.g. Norovirus
• Dormancy, hardiness, resistance to disinfectants
• Will germinate when conditions become favorable
• Regulated at molecular level

Question 10

Clostridium difficile

Answer 10

• Gram positive, anaerobic, spore forming bacillus
• Vegetative cells die quickly when exposed to the environment (aerobic)
• Spores can survive for long periods in the environment
• Sporulation is regulated by the alternative sigma factor SigH

Question 11

Antigenic variation

Answer 11

• Mechanism by which organisms change their surface proteins in order to evade the immune response
• Generates heterogeneous population
• Usually not reversible

Question 12

Molecular switching

Answer 12

• Phase variation
• Able to turn on/off
• Usually reversible
• Change the complete phenotype or population