Principles of Infection I

Question 1

What is symbiosis?

Answer 1

• living together - eg. microbes require human to survive + multiply
• does not distinguish between relationships that are harmful or beneficial to either party

Question 2

What is commensalism?

Answer 2

• microbe derives food/shelter from host
• normally does not harm

Question 3

What is mutualism?

Answer 3

• symbiosis which is beneficial to both organisms involved

Question 4

What is another term for commensals?

Answer 4

Normal flora

Question 5

Where are normal flora found?

Answer 5

• nose, nasopharynx + upper resp tract
• oral cavity - large bowel
• lower female genital tract
• skin

Question 6

What do normal flora/commensal microbes tend to do?

Answer 6

• COLONISE the host

Question 7

What is a pathogen?

Answer 7

A microbe that causes disease / harm to the host

Question 8

In which 3 instances can commensals be pathogenic?

Answer 8

• immunosuppression (eg. leukemia) -> OPPORTUNISTIC INFECTION
• commensal at 1 site, pathogen at another (eg. SA in nose vs post-op wound)
• commensal bypasses normal defences -> enters sterile site

Question 9

What are some normally sterile sites?

Answer 9

• lower resp tract
• blood
• bone, joint + subcutaneous tissue
• female upper genital tract
• urinary tract
• CNS - CSF + eye
• other viscera eg. liver, spleen, pancreas

Question 10

What is meant by the term ‘virulent’?

Answer 10

Highly pathogenic microbes

Question 11

What two things can fall out of balance to result in infection?

Answer 11

When the pathogenic mechanisms are STRONGER than the defensive mechanisms

Question 12

What are the 6 stages of infection?

Answer 12

1) survival of microbe + spread to host
2) adherence of microbe to host + entry
3) multiplication
4) evasion of host defences
5) damage to host
6) shedding of microbe + spread to env/other host

Question 13

What are some routes of spread for pathogens?

Answer 13

• airborne/droplet - tb, influenza
• GI tract - salmonella, cholera
• through skin - malaria
• inanimate objects - mrsa, rsv
• other epithelial surfaces (oral, genital) - ebv, gonorrhoea

Question 14

What is a fomite?

Answer 14

any nonliving object or substance capable of carrying infectious organisms eg. a teddy bear

Question 15

What are some local symptoms of infection?

Answer 15

• redness, swelling, warmth, pain, loss of function
• pus - pyogenic infection

Question 16

What are some systemic symptoms of infection?

Answer 16

• fever, rigors, chills, tachycardia, tachypnoea