Culture-medium meaning

Each bacterium capable of growth gives rise to a colony visible to the naked eye, and if the colonies are sufficiently apart, an inoculation can be made from any one to a tube of culture-medium and a pure culture obtained.

For example, various sugars - lactose, glucose, saccharose, &c. - are added to test the fermentative action of the bacterium on these substances; litmus is added to show changes in reaction, specially standardized media being used for estimating such changes; peptone solution is commonly employed for testing whether or not the bacterium forms indol; sterilized milk is used as a culture medium to determine whether or not it is curdled by the growth.

Such toxins being set free in the culture medium are often known as extracellular.

A special culture medium is needed to grow Yersinia.