Cystine Glucose blood agar is also known as Cystine Heart Agar. Francis developed blood-dextrose-cystine agar after determining F. tularensis would only grow on an artificial medium supplemented with sulfhydryl compounds (i.e., cystine). F. Tularensis is extremely meticulous organism that requires cystine to grow at its best. To honor the achievements of all time of Francis in the field of understanding the disease it was named Francisella Tularensis. The hemoglobin-rich medium is suggested to cultivate Francisella Tularensis. Without enrichment supplies, it facilitates the growth of cocci gram-negative and other pathogenic organisms.
Principle of Cystine Glucose Blood Agar
It is an extremely nutritious medium and is the best medium to isolate F. Tularensis. It could also be utilized to cultivate other organisms that are generally difficult to cultivate. It contains infusions from beef heart, proteose and peptone. is a source of nitrogen and vitamins, and L-Cystine is the main source from amino acids. Dextrose is an energy source for carbon. The sodium chloride is a source of Ions and helps maintain the balance of osmotic equilibrium. Agar is the agent responsible for forming solids. The addition of 2% hemoglobin gives you additional nutrition and factors for growth. If you do not enrich, Cystine Glucose Blood Agar helps to promote the growth of cocci gram-negative and various pathogenic microorganisms.
Composition of Cystine Glucose Blood Agar
| Ingredients | Gms/L |
| Infusion from Beef heart | 500.0 |
| Proteose peptone | 10.0 |
| Dextrose | 10.0 |
| Sodium chloride | 5.0 |
| L-Cystine | 1.0 |
| Agar | 15.0 |
Final pH (at 25°C) 6.8±0.2
Preparation of Cystine Glucose Blood Agar
- Suspend 51 grams of food in 1000 milliliters of distilled water.
- Then heat to boiling, allowing the medium to completely dissolve the medium.
- Sterilize using autoclaving at 15lbs tension (121degC) over 15 mins.
- To enhance the hemoglobin concentration (2 percent) For hemoglobin enrichment, dissolve 10.2 grams of medium into 100ml of distilled water.
- Sterilize with autoclaving with 15 lbs pressurization (121degC) during 15 minutes.
- Cool the medium until it reaches 50 degrees Celsius and aseptically add 100ml of sterile hemoglobin 2% solution.
- Mix well, then pour into sterilized Petri plates.
Results Interpretation on Cystine Glucose Blood Agar
- In the 24 hours of the day, colonies are extremely small and cannot be observed.
- After the time of 48 hours, F. Tularensis colonies are 1-2 millimeters in size, from grey to white to bluish-grey and flat, opaque with an entire edge smooth and shiny surface.
Uses of Cystine Glucose Blood Agar
- It is employed in quantitative methods for the cultivation of Francisella Tularensis.
- Without enrichment, Heart Infusion Agar with dextrose at 1% and 0.1 percent cystine helps to support the growth of cocci gram-negative as well as other microbes that cause disease.
Limitations
- It is suggested that immunological, biochemical, mass spectrometry or molecular testing be carried out on the colonies of pure culture for a complete identification.
- F. Tullensis is very infectious and are transmitted via droplets or aerosols therefore clinical specimens should be handled with extreme care and suspect specimens containing F. Tularensis must be handled in accordance with Biological Safety Level-2 (BSL-2) procedures. BSL-3 guidelines are recommended for all manipulations of the culture immediately after F. Tularensis is discovered.
