Microbiology

Question 1

What is commensalism?

Answer 1

association between organisms where one benefits and other neither gains nor harms

Question 2

Describe gram-staining

Answer 2

crystal violet - iodine treatment - decolourisation - safranin as counter-stain

gram-positive = retain violet (shows up purple/blue)
gram-negative = do not retain violet (shows up pink/red)

Question 3

Living + non-living characteristics of viruses

Answer 3

Living = can reproduce (but only in host cells), can mutate
Non-living = acellular (no organelles), no metabolism on own, most possess RNA or DNA but not both

Question 4

What is a prion?

Answer 4

protein-containing particles - no detectable nucleic acid
highly resistant infectious agent
no inflammation or immune response unaffected

Question 5

Describe antibiotic resistance

Answer 5

resistant + non-resistant bacteria exist
bacteria that have resistant DNA may transfer a copy of these genes to other bacteria
non-resistant bacteria become resistant
in presence of drugs, only drug-resistant bacteria survive
drug-resistant bacteria multiply + thrive

Question 6

Antibiotic resistance causes

Answer 6

over-prescription of antibiotics
patients not completing antibiotic course
overuse of antibiotics in livestock + fish farming
poor healthcare infection control
poor hygiene + sanitation
absence of new antibiotics discoveries

Question 7

Drug-resistant superbugs examples

Answer 7

MRSA (methicillin-resistant staphylococcus aureus)
Clostridium difficile
ESBL (extended spectrum beta-lactamases)
VRE (vancomycin-resistant enterococcus)

Question 8

List innate mechanical defences to infection

Answer 8

Respiratory tract (nasal hair, secretions, mucociliary apparatus)
GI tract = secretions, stomach pH, peristalsis
Skin = waterproof, tight junctions

Question 9

List innate chemical defences to infection

Answer 9

Lysozyme
Iron-binding proteins (eg lactoferrin)
Defences (eg cathelicidins)

Question 10

How does skin protect against infection?

Answer 10

tight junctions between epithelial cells = physical barrier to pathogens

Question 11

How does mucus prevent against infection?

Answer 11

viscous = traps pathogens
mucus on top of cells with cilia
cilia wafts mucus towards throat to be swallowed/coughed up
contains antimicrobial proteins (eg lysozyme)

Question 12

List methods of infection spread

Answer 12

• airborne (tiny particles)
• droplet (larger particles)
• vertical transmission (mother to baby from vagina, bloodstream or breastmilk)
• faecal oral
• sex
• food/waterborne
• via needles

Question 13

Methods to prevent community-acquired infection

Answer 13

reduce susceptible population (immunisation)
reduce infectious population (diagnosis + treatment)
reduce person-person spread (handwashing, food hygiene, safe sex etc)
preventing animal-human spread (pasteurise milk, kill infected livestock, treat animals)