different agars

[SKA]

how is tryptone soy agar different from nutrient agar?
How do they affect different bacteria?
anyone any info or links for them please?

[theprof]

Tryptone soy agar is technically a Soybean-Casein Digest Agar. TSA consists of agar, pancreatic digest of soybean meal, pancreatic digest of casein and sodium chloride, although there are sometimes slight variations from manufacturer to manufacturer � I required one a few months ago that also had a small quantity of glucose. The pancreatic digests provide the carbon, vitamins and nitrogen required and the sodium chloride provides osmotic balance. As well as tryptone soy agar and TSA, it is also known as tryptic soy agar and trypsin soy agar

TSA is probably the best general purpose nutrient medium. The medium is excellent for both fastidious and non-fastidious organism growth and can be used to cultivate a wide-range of moulds, fungi, bacteria and yeast. It is suitable for aerobic and anaerobic microorganisms. A substantial amount of TSA is used in hospital laboratories. Most species of Staphylococcus, Pseudomonas and Salmonella grow excellently in the medium. Culture maintenance is simple in comparison to nutrient agar and TSA is the medium of choice for good growth where advanced facilities are often not available such sixth-form colleges or high schools. In environmental laboratories, it is often the medium of choice for coliform identification.

(continued)

[theprof]

Often TSA is used only as a nutritious base and is enhanced with a variety of supplements including bovine or sheep blood. Around 5% of defibrinated blood will provide a suitably opaque medium. Some organisms such as Haemophillus and Neisseria spp prefer blood supplemented TSA which has been heated to 80 degrees C for a few minutes resulting in a chocolate-brown medium. Other additives such as yeast extract will often demonstrate a manyfold increase in organism growth. In the UK, TSA is available from many suppliers although we have found that Oxoid TSA maintains a consistently high quality. It is important to discard any TSA powder that does not free-flow or appears lumpy and/or unevenly coloured.

[theprof]

Nutrient agar is predominantly used for the growth of non-fastidious organisms. It is a relatively simple mixture of peptone, beef extract and agar. As a result it is often insufficiently nutritious for the growth of many bacteria and fastidious bacteria will often show no growth at all.

Pathogenic organisms tend to grow poorly in nutrient agar and where there is a risk of pathogenic growth due to the uncertainty of the micro-organisms present, it is often the medium of choice. Therefore, just like TSA, it is often used in school environments. Nevertheless, nutrient agar finds use in the dairy, pharmaceutical, water , fisheries and sewage industries and just like TSA it will grow moulds, fungi, bacteria and yeast as long as they are not too nutritionally demanding. Sometimes certain fungi spp will show no growth at all in nutrient agar so the medium is best avoided if a demonstration of fungal growth is required.

There are varieties of nutrient agar that contain vegetable derived peptone rather than animal peptone. Pseudomonas aeruginosa manufactures pyocyanin in nutrient agar which causes a turquoise colouration in the medium. Nutrient agar is available from many suppliers and tends to be fairly consistent in quality. Once again, any of the powder that does not free-flow or appears lumpy and/or unevenly coloured should be discarded.