Introduction to Medical Microbiology

Question 1

List the categories of micro-organism that cause disease.

Answer 1

o	Bacteria
o	Viruses
o	Fungi
o	Parasites
o	Prions

Question 2

List the common specimen types collected for culture.

Answer 2

o	UTI’s – Mid-stream Urine Sample
o	Chest Infection – Sputum
o	Tonsillitis/Pharyngitis – Throat Swab
o	Wound of site of infection – Swab of pus/tissue
o	Diarrhoea – Stool Sample
o	Bacteraemia – Blood culture
o	Meningitis – CSF sample

Question 3

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

Answer 3

Microscopy allows for the staining and quick detection (but not identification) of bacteria in samples. It is however, insensitive.

Cultures allow bacteria to be grown overnight on a specific medium. The colonies are visible to the naked eye after incubation. The strains can then be identified by colonial appearance and growth patterns. Growth of cultures can be slow though.

Question 4

Explain the difference between sterile and non-sterile sites.

Answer 4

Sterile sites should contain no micro-organisms, commensal or otherwise. These sites include:
o	Blood
o	CSF
o	Bladder
o	Lungs
Non-sterile sites however, can contain commensal microbes that may not harm the body, but still show up in microscopy or cultures.
o	Skin
o	Nasopharynx
o	Urethra
o	Gut

Question 5

Outline the methods of detecting viruses

Answer 5

Viruses can only grow inside other cells, so a cell line must be inoculated. Light microscopy cannot detect viruses, so electron microscopy is used instead. Antigen detection and nucleic acid amplification is more widely used now as a method of diagnosis. Serology is less common, but can still be used to determine immunity. PCR can be used.

Question 6

Define parasites

Answer 6

Parasites - an organism which lives in or on another organism (its host) and benefits by deriving nutrients at the other’s expense