Chocolate agar ( obsolete agar with heated blood ) is a nutrient medium enriched with heat-lysed blood or hemoglobin , which is used to isolate and cultivate pathogenic bacteria with high nutritional needs [1] [2] . The nutrient medium was named for its characteristic color and does not contain chocolate or cocoa . Conventionally, chocolate agar can be called a type of blood agar , however, these environments differ in purpose and method of preparation.
Content
- 1 Composition and preparation
- 2 Application
- 3 See also
- 4 notes
- 5 Links
Composition and preparation
A wide spectrum of solid nutrient media used in microbiology is used as the basis for chocolate agar [3] . 5-10% of animal blood is added to the molten sterile base and heated in a water bath at a temperature of about 80 ° C for 5 minutes in order to lyse red blood cells and inactivate enzymes that destroy growth factor V. In some cases, for example, when using the blood of pigs or goats, the heating temperature can be 100 ° C, and the heating time is increased to 15 minutes [4] .
Often, for the preparation of chocolate agar, a suspension sterilized in autoclave made from dry hemoglobin is used instead of blood. Due to the fact that hemoglobin is not a complete replacement for blood, synthetic growth supplements containing NAD necessary for the growth of bacteria of the genus Haemophilus , as well as vitamins and substances that stimulate the growth of gonococci and meningococci, are added to the nutrient medium [3] [5] .
Application
Chocolate agar is used to grow nutrient- demanding bacteria , such as gonococcus ( Neisseria gonorrhoeae ) and meningococcus ( Neisseria meningitidis ) [6] . In addition, some pathogenic bacteria (in particular, Haemophilus influenzae ) need additional growth factors V and X [7] , which are located inside red blood cells ( red blood cells ). For the successful growth of such bacteria, lysed (destroyed by the method of slow heating) red blood cells are necessary. A temperature of 80 ° C also inactivates enzymes that could metabolize NAD ( Nicotinamide Adenine Dinucleotide ).
Unlike blood agar, hemolysis does not occur during the cultivation of microorganisms on chocolate agar. Moreover, some α- and β-hemolysing microorganisms that produce hydrogen peroxide form green areas on chocolate agar similar to α-hemolysis [8] .
The addition of bacitracin to chocolate agar makes it an elective culture medium selective for the genus Haemophilus . The Thayer-Martin chocolate agar variant contains a whole range of antibiotics and is an elective culture medium for the cultivation of various types of gram-negative diplococci of the genus Neisseria .
See also
- Agar agar
- Culture medium
- Petri dish
- Blood agar
Notes
- ↑ Segen Chocolate agar: Definition . The Free Dictionary. Date of treatment January 6, 2015.
- ↑ Anderson, Cindy. Great Adventures in the Microbiology Laboratory. - 7th. - Pearson, 2013 .-- P. 175. - ISBN 978-1-269-39068-2 . (eng.)
- ↑ 1 2 Atlas, Ronald M.,. Handbook of microbiological media . - Taylor & Francis, 2010-01-01. - ISBN 9781439804087 .
- ↑ Chandar Anand, Rhonda Gordon, Helene Shaw, Kevin Fonseca, Merle Olsen. Pig and Goat Blood as Substitutes for Sheep Blood in Blood-Supplemented Agar Media // Journal of Clinical Microbiology. - 2000-02-01. - Vol. 38 , iss. 2 . - P. 591-594 . - ISSN 0095-1137 .
- ↑ JE Martin, TE Billings, JF Hackney, JD Thayer. Primary isolation of N. gonorrhoeae with a new commercial medium. // Public Health Reports. - 1967-04-01. - T. 82 , no. 4 . - S. 361–363 . - ISSN 0094-6214 .
- ↑ Gunn, BA Chocolate agar: A differential medium for gram positive cocci . PubMed Date of treatment January 6, 2015.
- ↑ Bergey's Manual of Systematic Bacteriology (English)
- ↑ Einar Leifson. Types of Bacteria on Blood and Chocolate Agar and the Immediate Cause of These Types // Journal of Bacteriology. - 1932. - T. 24 , no. 6 . - S. 473–487 . - ISSN 0021-9193 .