Medical microbiology

Question 1

What are categories of microorganism that cause infection?

Answer 1

• Bacteria
• Viruses
• Fungi
• Parasites
• Prions

Question 2

What are the two main sites of specimen collection?

Answer 2

Sterile and non-sterile sites

Question 3

What are examples of sterile sites?

Answer 3

Bloods
CSF
Lung
Bladder

Question 4

What are examples of non-sterile sites?

Answer 4

Skin
Nasopharynx
Urethra
Gut

Question 5

Give examples of infections and how you would sample them

Answer 5

UTI - Mid-stream urine
Chest infection - sputum
Tonsilitis/pharyngitis - throat swab
Wound or site infection - swab or pus
Diarrhoea - faeces
Bacteraemia - blood culture
Meningitis - cerebro-spinal fluid

Question 6

What is the role of microscopy in diagnosis of bacterial infection?

Answer 6

Useful technique for sterile samples where you want to get a quick result.

Gives in initial idea of the type of bacteria

Question 7

What is the role of Gram stain in diagnosis of bacterial infection?

Answer 7

Relatively quick test that lacks sensitivity

Can’t usually identify particular species

Question 8

What is the role of bacterial culture in diagnosis of bacterial infection?

Answer 8

Sensitive
Can identify different bacterium and stave off others depending on what conditions you’re interested in
Slow, can take a couple of days or up to a week for TB

Question 9

Conditions you can alter for bacterial culture

Answer 9

Type of media, non-selective (blood, chocolate) or selective (MacConkey)
Atmosphere
Temperature
Duration of incubation

Question 10

How do you detect viruses?

Answer 10

• Molecular methods, real time PCR
• Antigen detection
• Serology
• Rarely used methods, electron microscopy or cell or tissue culture

Question 11

How do you diagnose parasites?

Answer 11

• Microscopy: parasites, cysts, ova in faces or blood films for malaria
• Sometimes serology to see past exposure