Lecture 3: microbial pathogenesis

Question 1

Koch’s postulates

Answer 1

1. suspected germ must be present in every case of disease
2. germ must be isolated and grown in pure culture
3. cultured germ must cause disease when inoculated into a healthy host
4. same germ must be reisolated from the diseased experimental host

Question 2

gold standard in establishing cause of infection

Answer 2

PCR

• identifies cause of disease using a single copy of DNA or RNA
• potential problems due to normal flora

Question 3

colonization

Answer 3

• involves a transient or permanently established microbial growth
• NO interference with normal body function

Question 4

Infection

Answer 4

• involves a transient or permanently established microbial growth
• may manifest disease

Question 5

disease

Answer 5

• abnormal condition of body structures and function
• occurs when interaction leads to pathogenesis
• CAN occur without presence of microbe
  
  • toxins from microbes can cause intoxications

Question 6

how can different organisms lead to disease with similar signs and symptoms

Answer 6

due to similar pathogenicity mechanisms

• ex: conjunctivitis

Question 7

how can the same organims lead to disease with different signs and symptoms

Answer 7

• due to different pathogenicity mechanisms

Question 8

stages of disease: incubation (preclinical) stage

Answer 8

• pathogen has entered body
• no signs or symptoms
• innate immune system has not been activated
• not contagious

Question 9

stages of disease: Prodromal (warning) stage

Answer 9

• appearance of signs and symptoms (non specific)
• activation of innate immune system
• pathogen numbers increase
• easily transmitted even before person realizes they are sick

Question 10

stages of disease: acute stage; clinical illness

Answer 10

• most severe time of illness
• characteristic signs and symptoms
• acquired immune system has been activated
• pathogen numbers are stationary
• communicable diseases are easily transmitted

Question 11

stages of disease: decline stage

Answer 11

• illness is still apparent but signs and symptoms dwindle
• immune system activity is reduced (Antibodies formed)
• pathogen cleared from host
• can be contagious if individual becomes carrier

Question 12

stages of disease: convalescent stage

Answer 12

• patient returns to full health
• signs and symptoms end
• no immune system activity
• not contagious

Question 13

mechanisms of bacterial virulence

Answer 13

• metabolites
• invasins
• adhesins
• toxins

Question 14

mechanisms of bacterial virulence: tissue damaging metabolites

Answer 14

• acids, gases, or other byproducts of metabolism formed during bacterial growth
• serve to directly damage host tissues
• ex: strep mutans produces lactic acid which results in dental caries

Question 15

mechanisms of bacterial virulence: invasins or “spreading factors”

Answer 15

• proteins or enzymes that act locally to damage host cells
• affect tissue matrices and intracellular spaces
  
  • allow for spread and replication of bacterium

Question 16

mechanisms of bacterial virulence: adhesins

Answer 16

• bind pathogens to receptors on host cells and tissues
• most bind to glycoproteins

Question 17

name 3 types of adhesins

Answer 17

1. glycocalyx material
   
   1. capsule and slime layers
2. fimbriae and pili
   
   1. attach to specific host molecules
3. afimbrial adhesins
   
   1. proteins associated with cell envelope (wall/membrane)

Question 18

mechanisms of bacterial virulence: toxins

Answer 18

proteins with high activity and specificity and are heat labile

Question 19

exotoxins are found in gram cells

Answer 19

both gram negative and positive cells

Question 20

exotoxins

Answer 20

• proteins taht are toxic to cells, usually direct in action
• secreted into the extracellular fluid or assocaited with the bacterial cell surface
• bind host cell receptors

Question 21

enterotoxins

Answer 21

exotoxins that cause GI signs and symptoms

Question 22

what are the two main categories of exo/enterotoxins

Answer 22

A-B exotoxins

Question 23

function of A and B in A-B exotoxins

Answer 23

• A- Attacks cells
• B- binds toxin to host receptor
  
  • after binding, A is transported into cell
  • can form toxoids

Question 24

toxoids

Answer 24

inactivated toxins

Question 25

superantigens

Answer 25

• toxins
• activate up to 40% T cells in absense of antigen
• result in massive release of cytokines

Question 26

name three membrane active exotoxins

Answer 26

1. proteases
   
   1. destroy protein in host cell (cell membrane)
2. lipases: destroy lipids in cell membranes
3. hemolysins: form pores in RBC and phagocytes

Question 27

Name endotoxin of gram negative organisms

Answer 27

• LPS (not very toxic until released)
  
  • O antigen
  • Lipid A

Question 28

virulence mechanisms: encapsulation

Answer 28

blocks phagocytosis

• ex: S. pneumoniae capsule

Question 29

virulence mechanisms: inactivation of antibody

Answer 29

• S. pneumoniae secretes IgA degrading proteases
• S. aureus binds to Fc region of IgG

Question 30

virulence mechanisms: intracellular growth

Answer 30

• escape detection so host can’t initiate an immune response

Question 31

virulence mechanisms: antigenic variation

Answer 31

• ability of a microbe to
  
  • change epitopes
  • present new antigens to immune system
  • initiates new cycle of disease

Question 32

Antigenic drift

Answer 32

• accumulation of genetic mutations
• alters protein products
• leads to variability in population
• form antigenically distinct strains

Question 33

Antigenic shift

Answer 33

• reassortment of viral genome
• in cell infected by 2 strains of influenza A
• produces a new subtype of virus
  
  • can create flu pandemics

Question 34

Antigenic switching

Answer 34

• can result from genetic conversion/shuffling
• due to recombination within group of genes
• results in new surface antigen, but no change in biological function