Mike lecture 3

A good streak plate has

individual colonies

Different bacteria require

different growth media

Two basic culture media

1. Undefined

2. Defined

Nautral/complex - undefined media

based on nutrient extracts from animals or plants

BHI

Defined Media

The entire chemical composition and concentrations are known

Media Types

1. Selective

2. Differential

3. Enriching

Selective media

Contains one or more agetns that are inhibitory to all organisms excepted those selected for by growth conditions or chemical

eg Colistin/naladixic acid agar

Differential Media

Contains factor that allows colonies of one bacterial species to demonstrate metabolic or culture characterisitcs that distinguish it from other bacteria growin on the plate

Enriching Media

Contains specific nutrients required for growth of a particular organism

eg. chocolate agar

Selective and differential media examples

Mannitol salt agar

MacConkey agar

Selective and differential media

Allows to isolate or identify particular media

Macconkey agar

Selective - bile salts inhibit growth of some organisms

Differentiates - lactose ferment sugar to produce lactice acid. Reduces pH. Indicator changes colour

Mannitol Media

Selective - 7.5% NaCl high salt inhibits most bacterial growth

Differentiates - Manitol and ph indicator turns pink to yellow

Enriched Media have

additional nutrients to enhance the growth of fastidious microbes but are non-selective

Advantages of cultivation media

Relativly cheap

Removes non-pathogenic strains and allows growth of pathogen

Ability to grow on medium helps identification

Growth of microorganisms means more cells which make identification easier

Disadvantages of cultivation media

Microbial growth can be slow

Some microbes difficult to grow

many viruses difficult to grow

Benefits of isolation

Clinical isolates - diagnostics microbiology

Environmental isolates - monitoring in the food industry, preparation of pharmaceuticals

Epidemiology (outbreaks) - tracking infection across countries

Medical Microbiology

Need to identify between virus and bacterial infection

Identify organism for treatment

Track spread of disease

Collection and handling of sample

store and transport in approriate environments

Transporting Media sample

Maintain viability

Three factors of hazard

liklihood to cause disease

How likely it is to spread

availability of treatment

Hazard group 1

Very unlikely to cause disease

Hazard group 2

Can cause human disease but unlikely to spread to community. Usually effective prophylaxis or treatment available

Hazard group 3

Can cause severe human disease. May spread to community. Usually and effective prophylaxis or treatment available

Hazard group 4

causes severe human disease. Likely to spread to community and no effective prophylaxis or treatment

Identifying disease