Pathogens in perspective

Question 1

Pathogenicity and virulence

Answer 1

Pathogenicity is an organism’s ability to cause disease

Virulence is a measure of the degree of disease that a pathogen causes

Question 2

Microbial antagonism

Answer 2

Bacterial flora prevent overgrowth of harmful microbes

Question 3

Environmental pathogen

Answer 3

Microorganisms that spend a substantial part of lifecycle outside of humans. When introduced to humans cause disease

Question 4

Gut microflora

Answer 4

Breaking of foetal membrane exposes infant to microbial world
Greatest diversity is in the colon
Anaerobic bacteria predominate
Bacteroides spp. (obligate anaerobe)

Question 5

Microbial entrance to body

Answer 5

Skin (nicks, abrasions, incisions)
Gastrointestinal tract
Respiratory tract
urogenital tract
Transplacental entry

Question 6

Infectious dose

Answer 6

Minimum number of microbes required for infection to proceed
Microbe with smaller ID has greater virulence
Measles (1 virus)
Typhoid (10,000 cells)

Question 7

Surviving host defences

Answer 7

Antiphagocytic factors
Leukocidins are toxic to white blood cells (Staphylococcus and streptococcus)
Slime layer or capsule makes phagocytosis difficult
Legionella pneumophila able to survive intracellular phagocytosis

Question 8

Virulence factors

Answer 8

Exoenzymes digest epithelial tissues and permit invasion

Endotoxins (LPS of gram-negative) and exotoxins (positive and negative)

Question 9

Latency

Answer 9

Microbe can remain and becomes periodically active (herpes virus)
Chronic carrier is latent person who sheds infectious agent