Niacin (nicotinic acid) is produced by all mycobacteria but some of them lack the enzymes to convert it further into nicotinamide
adenine dinuceotide (NAD). Thus, niacin accumulates in the culture medium from which it can be extracted with sterile water or
physiologic saline. M. tuberculosis accumulates the most, but other species may also return positive results: M. africanum, M. microti,
M. simiae and some strains of M. chelonae, M. marinum, and M. ulcerans.
In the presence of citric acid, chloramine-T and potassium thiocyanate will react to form cyanogen chloride. This compound will break
apart the pyridine ring of niacin to produce gamma-carboxy glutaconic aldehyde and joins an aromatic amine to form a yellow color.
Positive control: Mycobacterium tuberculosis ATCC 25177,
Negative control: Mycobacterium fortuitum ATCC 6841.
1. Young, W.D.; Maslansky, Alvin; Lefar, Lefar; Kronish, Donald (December 1970). "Development of a paper strip test for detection of
niacin produced by mycobacteria". Applied Microbiology. 20 (6): 939–945.
2. Niacin Reagent Strip. Remel leaflet. https://tools.thermofisher.com/content/sfs/manuals/IFU21090.pdf.
3. Bhalla, G. S., Sarao, M. S., Kalra, D., Bandyopadhyay, K., & John, A. R. (2018). Methods of phenotypic identification of non-tuberculous
mycobacteria. Practical Laboratory Medicine, 12, e00107.
NIACIN REAGENT COMPOSITION: potassium thiocyanate 30.0 g, chloramine-T 25.0
g, p-aminosalicylic acid 5.0 g, citric acid trihidrate 4.0 g, ethyl alcohol 50.0 ml,
demineralized water 150 ml.
NIACIN STRIP PROCEDURE
- Puncture the culture slant with a loop or with a Pasteur pipette. Niacin
production is extracellular and accumulates in the medium so, you have to
break the cell mass so that the medium is exposed.
- Add 1 ml of sterile distilled water in the culture tube.
- Place the tubes horizontally so the fluid covers the entire surface of the
- Wait for 30 minutes then turn the slants upright for 5 minutes to let fluid to
drain to the bottom.
- Transfer 0.5 ml of fluid in a new empty tube then insert the strip with the
identification end at the top. Close the tube immediately.
- Leave at room temperature for 15–20 minutes, agitating the tube occasionally.
- Observe the colour of the liquid in the bottom of the tube against a white
background. Positive result: a yellow color appears. Negative result: no color.
(c) Costin Stoica