1 Culture and Culture Media
A culture medium is a substrate that support the growth of microorganisms. Such media can be specially compounded or natural which may be soil or garbage, what ever a culture media is it must contain certain components tobe able to support microbial growth, these components maybe a source of carbon example carbohydrate, nitrogen example organic ones like amino acids and peptone or inorganic ones like ammonium nitrate and some growth factors like metallic ions, vitamins and water. For us to continue I will like us to know what a pure culture is: a pure culture is one that contains only a single kind of microorganisms. They are three types of culture media:
1) Natural or Emperical Culture Media.
2) Synthetic or Defined Culture Media.
3) Living Culture Media.
1) Natural or Emperical Culture Media: This include meat, blood , vegetable, milk just to name a few. Most natural media contain either one or a major ingredient example peptone( hydrolysed proteins) peptone sources are animals example meat or vegetable example soyabean and cotton seeds. To any of the Emperical media many different substances can be added for different purposes, for example blood can be added to infusion broth to become blood infusion broth, lactose maybe added to broth to become lactose broth
2) Synthetic or Defined Culture Media: These consiste only of dilute reproducible solution of chemically pure known organic and or inorganic compounds. The formulation and use of this media requires an exact knowledge of the nutritional requirements of the microorganism to be cultivated. Commercially available dehydrated powdered bottle mixture of a great variety are in use, which are prepared simply by adding weighed portion of the ingredients to the require amount of water following the manufacturer's instructions
3) Living Culture Media: Some microbes cannot grow on artificial media, so they require life cells for culture. Sheep embryos are commonly used for cultivation of viruses.
Rickettsiae, Chlamydiae and Ehrlichiae are obligate intracellular bacteria that require living culture media.
Culture media can be classified base on:
1)-Consistency we have;
a) Liquid Media: These are available for use in test tubes, bottles or flask. Liquid medium are sometimes refered to as broth example nutrient broth. In liquid medium, bacteria grow uniformly producing general turbidity.
b) Solid Media: Any medium can be made solid by addition of certain solidifying agents. Agar agar is the most commonly used solidifying agent. It has a melting point of 95 degrees centigrade and solidifies at 42 degrees centigrade
c) Semi solid media: Reducing the amount of agar to 0.2-0.5 renders a medium semi solid. Such media are fairly soft and are useful in demonstrating bacteria motility certain transport media such as Stuart's and Amies media are semi solid in consistency.
d) Biphasic media: Sometimes culture system comprises of both liquid and solid media in thesame bottle, this is known as Biphasic medium.
2)- Classification based on functional use
a) Basal Media: They are basically simple media that support the growth of most non fastidious bacteria. Examples include peptone water, nutrient broth and nutrient agar.
b) Enriched Media: Addition of extra nutrients in the form of blood, serum to a Basal Media makes them enriched. Enriched Media are used to grow fastidious bacteria. Examples blood agar, chocolate agar, New York City medium.
c) Enrichment Media: They are liquid media that serve to inhibit commendable in clinical specimens. This medium is used for those microbes which are in small numbers in the sample and whose growth is slower than other species present. The principle is to control the nutrient and culture conditions such as temperature, pH, Oxygen in such a way that it suites only a given species.
d) Differential Media: They contain dyes,reagents or chemicals which allows the observer to distinguish between types of bacteria colonies after incubation. Example include Macconkey's agar and thiosulphate citrate bile salt sucrose agar.
e) Selective Media: It contain specific chemicals which donot affect the growth of the bacterium to be isolated but inhibits the growth of other bacterial in the sample. Example addition of Sodium azide at specific concentration into a media selectively isolate Lactic acid bacteria.
