Infection Basics

Question 1

What is an infection?

Answer 1

invasion of a host tissue by micoorganisms, leading to damage

Question 2

What is disease caused by in an infection?

Answer 2

• microbial multiplication
• toxins
• host response (leading to classic infection symptoms)

Question 3

What is the difference between horizontal and vertical transmission of infection?

Answer 3

horizontal transmission is via contact, inhalation, ingestion etc.

vertical transmission is from mother to child e.g via breast milk

Question 4

What are the classical local and general symptoms of infection?

Answer 4

local- pain, discharge, coughing, sputum production, diarrhoea

general- pyrexia, general malaise, rash, headache, respiratory fatigue, septic shock

Question 5

What are some subclassifications of infectious agents?

Answer 5

e.g

toxin mediated
acute pyogenic
sub acute
chronic granulomatous

Question 6

What actions would you carry out on suspicion of infection, in clinical practice?

Answer 6

• full history
• testing which included full blood count + CRP
• tests to identify causative agent:

bacteriology- e.g. agar 18h incubation, microscopy, gram staining, PCR

virology- antigen detection, antibody detection

Question 7

How can organisms be classified? (obligate, facultative, anaerobes etc)

Answer 7

Obligate anaerobes are microorganisms killed by normal atmospheric concentrations of oxygen (unless spore forming e.g clostridium)

A facultative anaerobe is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation or anaerobic respiration if oxygen is absent.

An obligate aerobe is an organism that requires oxygen to grow.

Question 8

Describe the process of gram staining

Answer 8

1) crystal violet added
2) iodide added

These form a complex within the peptidoglycan layer of the bacteria.

3) ethanol added

washes out the the stain from thin peptidoglycan layers in gram negative bacteria

4) counterstain added

gram positive bacteria=violet
gram negative bacteria=red

Question 9

When isn’t gram staining appropriate?

Answer 9

mycobacterium require the ZN stain due to the thick, lipid rich wall

Parasites are detected in stool samples

Electron microscopy is used for virus identification

Fluorescence microscopy is used to identify RSV

Question 10

What are the benefits and drawbacks of culture dependent identification vs culture independent?

Answer 10

culture dependent:

• slow
• organims must be alive
• low yield post antibody response
• can test other properties e.g. sensitivity
• sensitive and specific

Question 11

What are some differences between eukaryotes and prokaryotes?

Answer 11

prokaryotes have circular dna plasmid with no nuclear envelope or nucleoli. no membrane bound organelles. cell wall usually present. 70S ribosomes.