An Introduction to Medical Microbiology

Question 1

List the categories of micro-organisms that cause infection

Answer 1

1) Bacteria
2) Viruses
3) Fungi
4) Parasites
5) Prions - an abnormal form of a normally harmless protein found in the brain.

Question 2

List the common specimen types collected for culture

Answer 2

Sterile sites - blood, CSF, lung and bladder
Non - sterile sites - skin, nasopharynx, urethra, gut.
e.g. UTI - MSU
Chest infection - sputum
Tonsilitis - throat swab
Wound - swab of pus
Diarrhoea - Faeces
Bacteraemia - blood culture
Meningitis - CSF

Question 3

Microscopy

Answer 3

It takes only a few minutes to prepare a sample for microscopy so it is very quick however at 1000x magnification it can be easy to miss things. Viruses are not visible in light microscopy.
Unstained - pus cells, parasites
Gram stain - bacteria, yeast, fungi
ZN/auramine - mycobacteria

Question 4

Bacterial cultures

Answer 4

Used more often as they are sensitive to species but are slower than microscopy. You need some knowledge of organism in order to pick the best agar base. Culture conditions such as the media, atmosphere, temperature and duration can all affect the culture.

Question 5

Sterile site

Answer 5

Not normally associated with different organisms so any find is relevant making identification easier.

Question 6

Non - sterile site

Answer 6

Lots of organisms associated with the site

Question 7

Methods of detecting viruses

Answer 7

1. Molecular methods e.g. real time PCR
2. Antigen detection
3. Serology (blood test to detect antibodies)
   Rarely used
4. Electron microscopy
5. Cell or tissue culture

Question 8

Diagnostic principles of parasitology

Answer 8

1. Microscopy of different stages e.g. parasites, cysts and ova in faeces, blood films for malaria.
2. Culture is rarely possible
3. Serology is sometimes useful.

Question 9

Basic infection control measures

Answer 9

Hand hygiene, swab stethoscope between patients, isolation and barrier nursing