King's medium B

From Bugwoodwiki
(Redirected from Kings Medium B)


For distinguishing fluorescent pseudomonads from nonfluorescent pseudomonads


Ingredient 1 L 500 ml
Distilled water 1 L 500 ml
proteose peptone #3 (Difco) 20 g 10 g
K2HPO4 1.5 g 0.75 g
MgSO4•7H2O 1.5 g 0.75 g
glycerol 10 mL 5 ml
agar 15 g 7.5 g


  1. Mix water and peptone first
  2. Bring it to a boil and dissolve
  3. Add other chemicals
  4. Heat until all dissolve.


  • This medium is the best general isolation medium for bacteria. Fluorescent pseudomonads produce a yellow pigment that fluoresces under longwave ultraviolet light (366 nm). Some isolates from the P. syringae group don’t fluoresce.
  • This medium may not be suitable for longer term (more than 2 days) storage of Erwinia because some may die on it within a few days to a week.
  • It is important to use proteose peptone #3 and not other peptones in order to allow colonies to produce fluorescent pigments.
  • This mix is also commercially available as Difco Pseudomonas agar F.


  • Schaad, N. W. 1980. Laboratory Guide for the Identification of Plant Pathogenic Bacteria. The American Phytopathological Society, St. Paul, MN. 72 pp. (p. 3)

Contributed by

From the Virginia Tech Mediabook; Orignially created by Robert Wick; contributed by Mary Ann Hansen