AYERS AND JOHNSON AGAR (STOCK CULTURE AGAR)

Description

Maintenance medium are essentially designed to maintain the viability of cultures over an extended period of time. Stock Culture Agar was originally formulated by Ayers and Johnson. They observed that in addition to supporting luxuriant growth, the medium also helped in maintaining the viability of Streptococci and various other organisms over a long period of time. They also observed that Streptococci maintained their viability for as long as four months when incubated in this medium at room temperature (25?C). Stock Culture Agar serves its main purpose (i.e. maintaining viability) chiefly due to its semisolid nature, a well-buffered environment and the presence of casein and dextrose, the latter, which serves as a source of energy. Many fastidious organisms like Mycobacterium species, S. pneumoniae, show good growth on this medium. It can be made especially suitable for maintenance of Streptococci by the additions of L- Aspargine (1g/l).