Week 1 Intro

Question 1

What are the 4 common infective agents?

Answer 1

• Viruses
• Bacteria
• Fungi
• Parasites

Question 2

What are the 7 bacteria shapes?

Answer 2

• Coccus (circular)
• Bacillus (rod)
• Coccobacillus (round rod)
• Fusiform bacillus (pointy rod)
• Vibrio (curved rod)
• Spirillum (corkscrew)
• Spirochete (wiggly)

Question 3

What colour do Gram negative/positive bacteria stain and why?

Answer 3

Gram positive: Purple
- Thick peptidoglycan layer in the cell wall holds more of the crystal violet stain and retains it even after ethanol is added, thus staining the cells purple.

Gram negative: Pink
- Thin peptidoglycan layer in the cell wall does not hold the stain as well and is decolourized when the ethanol is added. Cell thus stains pink when safranin dye is added after ethanol.

Question 4

What is the difference between 1) commensal bacteria, 2) colonisation and 3) infection?

Answer 4

1) Commensal bacteria
- Bacteria that are commonly found in the human body and are not harmful
- May have beneficial effects on body

2) Colonisation
- The presence of more bacteria in an area, but with no infection or damage yet
- Usually in moist, warm body areas

3) Infection
- Invasion and multiplication of pathogens
- Produces tissue injury or disease

Question 5

In which group of people does bacterial colonisation increase in?

Answer 5

• Hospitalised patients
• Patients with medical conditions
• Patients given antibiotics (body flora has been changed and becomes more susceptible to other bacteria growing)

Question 6

What are the more common Gram positive bacteria? (9)

Answer 6

• Staphylococcus aureus
• Streptococcus pneumoniae
• Alpha-haemolytic strep
• Beta-hemolytic strep (A,B,C)
• Coagulase-negative staphylococci
• Enterococcus species
• Listeria monocytogenes
• Bacillus
• Corynebacterium

Question 7

What are some examples of Gram-negative bacteria? (6)

Answer 7

• Coliforms/Enterobacteriaceae
  ~ E. coli
  ~ Klebsiella
  ~ Enterobacter
• Pseudomonas aeruginosa
• Haemophilus
• Salmonella, Vibrio, Shigella, Campylobacter
• Neisseria meningitidis/gonorhhea
• Burkholderia pseudomallei

Question 8

What are some common Gram positive anaerobes?

Answer 8

• Clostridium spp
• Peptostreptococcus
• Actinomyces

Question 9

What are some Gram negative anaerobes?

Answer 9

• Bactreriodes fragilis
• Veilonella

Question 10

What are the tests usually done for 1) Viruses, 2) Bacteria, 3) Fungus, 4) Parasites, 5) Others?

Answer 10

• Virus: PCR and POCT
• Bacteria: Microscopy (Gram stain) , Culture and Sensitivity
• Fungus: Microscopy (fungal smear), Culture and Sensitivity
• Parasites: Microscopy
• Others/Virus + Parasite: Serology / Ab testing

Question 11

Factors of when bacterial culture results could be clinically insignificant or no growth?

Answer 11

• Depends on the type of bacteria
• Location of colonisation/infection etc
• If test is not sensitive enough
• If the test is formed too soon/too late after infection
• Poor sampling techniques (can also contribute to result contamination)