Cystine tryptic agar

Cystine tryptic agar (CTA), also known as cystine trypticase agar,^[1][2] is a growth medium used for the identification of microorganisms.^[3]

It can be used to determine if organisms can ferment various carbohydrates, including maltose, lactose, and sucrose. This approach can be used to type organisms because although strains quickly gain antibiotic resistance, they rarely gain the ability to metabolize new nutrients (though exceptions are known.) For example, the following fermentation patterns have been observed:

Organism	Fermentable sugars
Neisseria gonorrhoeae	glucose[4]
Neisseria meningitidis	glucose, maltose[4]
Neisseria lactamica	glucose, maltose, lactose[4]
Neisseria mucosa	glucose, maltose, sucrose[4]
Moraxella catarrhalis	none of the major sugars[4]

Typical composition

Cystine tryptic agar typically contains (w/v):^[5]

• 2.0 % casein
• 0.05 % L-cystine
• 0.5 % sodium chloride
• 0.05% sodium sulfite
• 0.25% agar
• 0.00017% phenol red
• 0.5% one of the sugars mentioned above

See also

• TSI slant