introduction to medical microbiology

Question 1

list the categories of microorganisms which cause disease?

Answer 1

• Bacteria
• Fungi
• Parasites
• Viruses
• Prions

Question 2

List the common specimen types collected for culture.

Answer 2

Bacteria:

• Tonsilitis- throat swab
• UTI- mid-stream urine
• Site of infection- blood, pus
• Meningitis- CSF
• Diarrhoea- faeces
• Chest infection -sputum

Not viruses, limited use with parasites.

Question 3

Outline the role of microscopy and bacterial culture in the diagnosis of infection

Answer 3

Light microscopy- magnification x1000- Allows the presence of a bacteria to be established.
Different types of stain:
- Gram stain- very rapid, non specific, used for bacteria
- Unstained- used for pus and parasites
- ZN stain used for bacterium

Bacteria culture:
Very slow, specific
Use different types of medium- specific or non-specific ( e.g. blood)
need to control: temperature, atmosphere, duration of incubation.
Grows overnight- can be seen by naked eye

Bacteria can be identified based on

• growth patterns and colonial appearance
• DNA tests
• typing- distinguishes between different species of bacteria.

In order to identify a bacterium:

• need to know likely site of pathogen
• need to know normal flora at site

Question 4

difference between a sterile and a non-sterile site?

Answer 4

sterile: usually free from bacteria.
Blood, CSF, Lungs, Bladder
Non sterile: usually inhabited with Bacteria.
Nasopharynx, gut, skin, urethra

Question 5

Outline methods for detecting viruses?

Answer 5

• Serology for immunity- i.e. production of antibodies
• Antigen detection
• Molecular methods e.g. PCR
• Electron microscopy
• Cell/tissue culture
• Light microscopy does not work

Question 6

Describe basic infection prevention measures?

Answer 6

• Hospital acquired infections e.g. MRSA and clostridium difficile- have high expected spectrum beta-lactadase ( ESBL)
• medical microbiologists work to diagnose, run labs, treat and prevent these infections
• wash hands before and between patients, isolate patients and keep materials sterile, swab stethoscope between patients

Question 7

Outline the principles of parasitology

Answer 7

Know there are 3 different sub catergories.

Know that they cannot be detected via light microscopy