B) Chocolate agar (CHOC)

> blood cells have been lysed by heating the cells to 56 °C

> used for growing fastidious (fussy) respiratory bacteria, such as Haemophilus influenzae.

Remember…

• Various categories of media are not mutually exclusive.
• Ex: blood agar is enriched and differential
• MacConkey agar and MSA are selective and differential
• PEA and CNA are enriched and selective
• Thayer-Martin and Martin-Lewis are highly enriched and highly selective
• Thioglycollate broth (THIO) is a liquid medium that supports the growth of all categories of bacteria.

Examples:

• Hektoen enteric agar (HEA) - selective and differential agar primarily used to recover Salmonella and Shigella from patient specimens
• Salmonella-Shigella agar (SS) – selective and differential for Salmonella and Shigella
• Bile Esculin Agar (BEA) is a selective differential agar used to isolate and identify members of the genus Enterococcus

Fungal Media

a) Sabouraud agar

> Sabouraud agar is used to culture fungi and has a low pH that inhibits the growth of most bacteria; also contains the antibiotic gentamicin to specifically inhibit the growth of Gram-negative bacteria.

b) Hay infusion agar

> Specific for the culturing of slime molds (though not technically fungi).

c) Potato dextrose agar

> PDA is used to culture of certain types of fungi.

Preparation of CM

• Nutrient Broth

¨ Dissolve 8 g of NB powder in 1000 ml of distilled water in an Erlenmeyer flask. Mix and heat over the magnetic stirrer until the medium becomes clear or transparent.

¨ Dispense 8 ml of the medium into sterile test tubes.

¨ Immediately stopper the tubes completely.

¨ Sterilize in the autoclave at 15 psi, 121 C for 15 mins.

• Nutrient Agar

¨ Dissolve 28 g of NA powder in 1000 l of distilled water in an Erlenmeyer flask. Mix and heat over the magnetic stirrer until the medium becomes clear or transparent.

¨ Sterilize in the autoclave at 15 psi, 121 C for 15 mins.

¨

Dispensing the CM

• NA plate

¨ Lay out several sterile Petri dishes on the table with the cover partially open and dispense the medium inside and inoculating hood.

¨ Dispense the NA medium (30 ml) and allow 5-10 minutes to elapse before completely covering the dish to avoid contamination.

¨ When the medium is solidified, label the NA plate. Wrap and label the plate.

• NA slant

¨ Dispense 8 ml of the medium into sterile test tubes using pipette or syringe.

¨ Cover the tube partially with sterile cotton plug or screw cap and allow the agar medium to harden in an incline position on an agar slant rack.

¨ Stopper the tube completely when the medium has solidified. Label the upper portion of the test tube slant.

¨ Sterilize in the autoclave at 15 psi, 121 C for 15 mins.

• NA deep or butt

¨ Dispense 8 ml of the medium into sterile test tubes using pipette or syringe.

¨ Cover the tube partially with sterile cotton plug or screw cap and allow the agar medium to harden in an upright position on a test tube rack.

¨ Stopper the tube completely when the medium has solidified. Label the upper portion of the test tube slant.

¨ Sterilize in the autoclave at 15 psi, 121 C for 15 mins.