Chocolate Agar was formulated in 1927 using peptones and yeast extract.1 Carpenter and Morton improved the recovery time of gonococci to 24 hours using GC Agar Base enriched with hemoglobin and yeast concentrate.2 the medium was further improved by replacing yeast concentrate with GCHI Enrichment, a chemically defined supplement formulated specifically to facilitate the growth of gonococci.3
This medium contains GC Agar Base which supplies casein and meat peptones necessary for bacterial growth, a phosphate buffer to maintain pH, and cornstarch to neutralize toxic fatty acids that may be present. Hemoglobin, when heated, releases hemin, the X factor required by fastidious organisms such as Haemophilus spp. GCHI Enrichment is a defined supplement which provides the V factor (NAD), vitamins, amino acids, coenzymes, dextrose, and ferric ions which promote growth of Neisseria spp.
Chocolate Agar is an enriched medium on which pathogenic bacteria may be overgrown with other nonpathogenic bacteria. Improved recovery of N. gonorrhoeae may be achieved using a selective medium, such as Thayer Martin Agar.
1. McLeod, J.W., B. Wheatley, and H.V. Phelon. 1927. Br. J. Exp. Pathol. 8:25.
2. Carpenter, C.M. and H.E. Morton. 1947. Proc. N.Y. State Assoc. Public Health Labs. 27:58-60.
3. Martin, J.E., Jr., T.E. Billings, J.F. Hackney, and J.D. Thayer. 1967. Public Health Rep. 82:361.
4. Murray, P.R., E.J. Baron, J.H. Jorgensen, M.L. Landry, and M.A. Pfaller. 2007. Manual of Clinical Microbiology. 9th ed. ASM Press, Washington, D.C.
5. Clinical and Laboratory Standards Institute (CLSI). 2004. Quality Control for Commercially Prepared Microbiological Culture Media; Approved Standard, 3rd ed. M22-A3. CLSI, Wayne, PA.