Pyridoxal disk is a reagent-impregnated to aid in the recovery of nutritionally variant streptococci (NVS) from clinical specimens.

In 1971, Cayeux et al. studied cultures in which NVS was isolated and found that they grew as satelliting colonies of other microorganims². Initial growth studies demonstrated that NVS require supplements such as pyridoxal hydrochloride or pyridoxamine dihydrochloride and various forms of vitamin B₆ for growth³. These bacteria often form pleomorphic, gram-variable cells especially when grown under less-than-optimal nutritional conditions⁴.

• Ready to use - Pyridoxal hydrochloride-impregnated disk
• Easy to store - No special storage required
• Easy to interpret - Zone of growth surrounding disk indicates that the organism is a nutritionally variant Streptococcus.

Pyridoxal disk consists of a dehydrated disk impregnated with pyridoxal hydrochloride. When the disk is placed on an inoculated blood agar plate, a zone of growth (NVS) appears around the disk after incubation. NVS can then be isolated in pure culture, biochemical and susceptibility tests can be performed, and isolates can be frozen for storage or transported to a reference laboratory⁵.