Introduction To Infection

Question 1

What is an infection?

Answer 1

Invasion of host’s tissues by micro organisms & disease caused by microbial multiplication, host’s response and toxin production.

Question 2

How do people get infections?

Answer 2

From themselves- microbiota are normally and naturally carried on skin and mucosal surfaces where they are harmless but transfer to other sites can be harmful.
From a source - from another person through physical contact ,airborne or by a vector(an intermediary).
From the environment- ingestion of contaminated food or water, inhalation of contaminated air or contact with contaminated surfaces ( medical equipment )

Question 3

What are the modes of horizontal transmission?

Answer 3

Contact : direct , indirect ,vectors
Inhalation: droplets -large particles above 5 microns in diameter and can travel 1-2 metres.
Aerosols- smaller and remain suspended in air and have a larger range.

Question 4

What are the modes of vertical transmission?

Answer 4

Mother to child before or after birth

Question 5

How do micro organisms cause disease? (Steps)

Answer 5

1. Exposure of host with microorganism
2. Adherence to a cell surface
3. Invasion: can be intracellular or to tissues and spread between cells in intracellular matrix
4. Multiplication
5. Dissemination into blood stream & to other patients

Question 6

What are virulence factors, give examples.

Answer 6

Chemicals that can enhance the survival of microorganisms and their reproduction within the host
Can be exotoxins or endotoxins.
Exotoxins include : cytolytic- membrane damaging
AB toxins- 2 part toxin where B binds to cell and delivers A to cytosol.
Super antigens- activate T cells
Enzymes- destroy tissue that bacteria are trying to invade.
Endotoxins: cell wall components that either cause direct host cell damage or as a result of the response to the virulence factors.

Question 7

What determines if a pathogen will cause disease?

Answer 7

Virulence factors 
Inoculum size 
Anti microbial resistance 
Site if infection 
Co-morbidities

Question 8

how do we investigate bacteriology and virology?

Answer 8

collect specimen 
antigen detection 
nucleic acid detection- only DNA in bacteria but RNA/DNA in virus
culture
antibody detection

Question 9

features of exotoxins

Answer 9

heat labile-capable of changing or destruction when subjected to heat
usually gram positive
highly toxic and antigenic
often enzymes

Question 10

features of endotoxins

Answer 10

heat stable lipopolysaccharide-protein complexes
form structural components of cell wall of gram negative bacteria
mildly toxic and antigenic
don’t bind to receptors