CTA Medium™ BD BBL™ 500 g. Cystine Trypticase™ Agar Medium. Culture medium for the maintenance of microorganisms. Also used for the detection of bacterial motility and, with added carbohydrate, for fermentation reactions of fastidious microorganisms, i. e. Neisseria, pneumococci, streptococci- and nonsporeforming anaerobes.