Which special disk is used to aid isolation of Abiotrophia?

Which special disk is used to aid isolation of Abiotrophia?

• A. Hemin disk
• B. Pyridoxal disk
• C. Vitamin B6 disk
• D. Catalase disk

Answer: (B)

Abiotrophia are nutritionally fastidious organisms that require pyridoxal (vitamin B6) for growth. To aid their isolation, labs use a disk impregnated with pyridoxal placed on the culture plate; the pyridoxal diffuses into the medium and allows growth of colonies nearby, resulting in satellite colonies around the disk. This growth pattern, driven by the organism’s dependence on pyridoxal, helps differentiate Abiotrophia (and related nutritionally variant streptococci) from other bacteria. The other options don’t address the growth factor Abiotrophia needs—hemin disks support X factor for Haemophilus, and catalase tests are not about growth requirements. Vitamin B6 disk conveys the same nutrient, but the established term used for isolation is pyridoxal disk.