DNase TEST AGAR with TOLUIDINE BLUE (DEOXYRIBONUCLEASE
ACTIVITY)
CAT Nº: 2028
For the detection of deoxyribonuclease activity to aid in the identification of
bacteria isolated from clinical specimens
FORMULA IN g/l
Casein Peptone
15.00 Deoxyribonucleic Acid
Soy Peptone
5.00 Toluidine Blue
Sodium Chloride
5.00 Bacteriological Agar
2.00
0.10
15.00
Final pH 7.3 ± 0.2 at 25ºC
PREPARATION
Suspend 42.1 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent
agitation. Boil for one minute until complete dissolution. Sterilize in autoclave at 121ºC for 15 minutes. Cool to 45-50ºC,
mix well and dispense into plates. The prepared medium should be stored at 8-15°C. The color is blue, slightly
opalescent. After autoclaving, the medium is green and turns blue after is cooled.
The dehydrated medium should be homogeneous, free-flowing and greenish-beige in color. If there are any physical
changes, discard the medium.
USES
DNase TEST AGAR with TOLUIDINE BLUE is used to differentiate microorganisms with DNase activity. This differential
medium is especially recommended for the identification of pathogenic Enterobacteria.
Casein peptone and Soy peptone provide nitrogen, vitamins, minerals and amino acids essential for growth. Sodium
chloride supplies essential electrolytes for transport and osmotic balance. Deoxyribonucleic Acid enables the detection of
DNase that depolymerize DNA. Bacteriological agar is the solidifying agent. DNase Test Agar with Toluidine Blue contains
a metachromatic dye to eliminate the necessity of reagent addition to the agar following incubation. Toluidine blue may
be toxic to some gram-positive cocci and, therefore, should be used primarily with Enterobacteriaceae.
Inoculate making a heavy band streak (2 cm in length) of the test organism on the surface of the plate. You can
simultaneously place 4 to 5 different samples on the same plate. Incubate for 48 hours at 35 ± 2°C. Toluidine Blue form
colored complexes with polymerised DNA.
In the presence of toluidine blue:
DNase-positive: Appearance of a pink halo surrounding the inoculum streak. The rest of the plate remains blue.
DNase-negative: Absence of the pink halo surrounding the inoculum streak.
MICROBIOLOGICAL TEST
The following results were obtained in the performance of the medium from type cultures after incubation at a
temperature of 35 ± 2ºC and observed after 148 hours.
Microorganisms
Serratia marcencens ATCC 14756
Enterobacter aerogenes ATCC 13048
Growth
DNase Test
Good
Good
+
-
1
LABORATORIOS CONDA, S.A.
www.condalab.com
BIBLIOGRAPHY
Blair E.B. Emerson, J.S. and Tull, S.C. Am. J.Clin.Poth, 47:30-39, 1957. Disalvo Med. Tech. Bull. 9:191. 1958.
Weckman and Catting J. Bact. 73: 747. 1957.
Smith, Hancock and Rhoden. 1969. Appl. Microbiol. 18:991.
STORAGE
25ºC
Once opened keep powdered medium closed to avoid hydration.
2ºC
2
LABORATORIOS CONDA, S.A.
www.condalab.com