Agar, Bacteriological No. 2 is a solidifying agent for use in preparing microbiological culture media in a laboratory setting. Agar, Bacteriological No. 2 is not intended for use in the diagnosis of disease or other conditions in humans.
Agar is a phycocolloid extracted from a group of red-purple algae, usually Gelidium spp. Agar was first suggested for microbiological purposes in 1881 by Fannie Hesse. By the early 1900’s, agar became the gelling agent of choice over gelatin because agar remains firm at growth temperature for many pathogens and agar is generally resistant to a breakdown by bacterial enzymes. The use of agar in microbiological media significantly contributed to the advance of microbiology, paving the way to study pure cultures.
Agar is a gel at room temperature, remaining firm at temperatures as high as 65°C. Agar melts at approximately 85 - 91°C, a different temperature from solidification at 34 - 36°C. This property is known as hysteresis. Agar is generally resistant to shear forces; however, different agar may have different gel strengths or degrees of stiffness.
Specifications for Agar, Bacteriological No. 2 include good clarity, controlled gelation temperature, controlled melting temperature, good diffusion characteristics, absence of bacterial inhibitors, and the presence of metabolically useful minerals such as calcium and magnesium. Agar, Bacteriological No. 2 is recommended for various applications, auxotrophic studies, bacterial and yeast transformation studies, and bacterial molecular genetics applications.
