NUTRIENT GELATIN

Cat. no. Q23 Nutrient Gelatin, 15x103mm Tube, 6ml Deep 20 or 100 tubes/box

INTENDED USE

Hardy Diagnostics Nutrient Gelatin is used to aid in classification of the Enterobacteriaceae by determining an organisms ability to liquify gelatin.

SUMMARY

Gelatin was the substance originally used to gel culture media. However, gelatin is liquid at 35ºC., the optimum temperature for many bacteria. In addition, some bacteria are capable of liquifying the gelatin, making it an unsuitable solidifying agent. Agar, gelatin's replacement, has neither of these drawbacks.

The breakdown of gelatin is a result of the production of the enzyme gelatinase by an organism. The purpose of this proteolytic enzyme is to break down large molecules so that they can be brought into the cell to be metabolized. This ability to liquify gelatin is characteristic of certain Enterobacteriaceae such as Proteus species and Serratia species.

FORMULA

Ingredients per liter of deionized water.*

Gelatin 120.0gm
Peptone 5.0gm
Beef Extract 3.0gm

Final pH 6.8 +/- 0.2 at 25ºC.

* Adjusted and/or supplemented as required to meet performance criteria.

STORAGE AND SHELF LIFE

Storage: Upon Receipt store at 2-8ºC. away from direct light. Media should not be used if there is any sign of deterioration (shrinking, cracking, or discoloration), contamination, or if the expiration date has passed.

PRECAUTIONS

PROCEDURE

1. An 18-24 hour isolate, in pure culture should be used to prepare the inoculum for this test.

2. Using a heavy inoculum and an inoculating needle, stab the solid media to a depth of approximately one half to one inch from the bottom of the tube.

3. An uninoculated control tube should be taken, in parallel, through the rest of this procedure.

4. Incubate for 24 hours and up to 14 days, checking for evidence of growth and gelatinase activity. The gelatinase test must be run at 20ºC. Tubes can be placed at higher incubation temperatures for organisms that require it, but the tubes must be chilled below 20ºC. prior to reading the test. Chill the tubes by placing them in a refrigerator (20ºC.) or an ice bath until the control tube solidifies.

Note: Some organisms may require 30 days to six weeks of incubation in order to show visible gelatin liquifaction.(2)

Note: If the uninoculated control becomes liquified, the test is not valid.

INTERPRETATION OF RESULTS

A positive test for gelatin liquifaction is for the media to remain liquid after the refrigeration period. A negative test will remain solid after being cooled. An uninoculated control tube should be run in parallel with each set of tubes set up on a given day. If liquifaction occurs in the sterile control after cooling to 20ºC. the results of the test should be disregarded.

LIMITATIONS

A control tube must be run in parallel with each test. One control tube can be used for all organisms being tested, if all tubes are inoculated at the same time.(2)

If the tubes are incubated at temperatures of greater than 20ºC., the tubes must be chilled below 20ºC. before reactions can be determined.(2)

Do not shake the tubes after incubation, as some positive liquifaction reactions will be missed.(2)

Fastidious bacteria may not grow in Nutrient Gelatin.

MATERIALS REQUIRED BUT NOT PROVIDED

Standard microbiological supplies and equipment such as loops, other culture media, swabs, applicator sticks, incinerators, and incubators, etc., as well as serological and biochemical reagents, are not provided.

QUALITY CONTROL

Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Escherichia coli
ATCC ® 25922
D up to14 days 35°C Aerobic Growth; no liquifaction
Staphylococcus aureus
ATCC ® 25923
D up to14 days 35°C Aerobic Growth; liquifaction
Clostridium perfringens
ATCC ® 13124
D up to14 days 35°C Aerobic Growth; liquifaction
Bacillus subtilis
ATCC ® 6633
D up to14 days 35°C Aerobic Growth; liquifaction

User Quality Control

PHYSICAL APPEARANCE

Nutrient Gelatin should appear as a clear and colorless.

Positive (bottom) and Negative (top) Nutrient Gelatin Tests

Showing positive (lower tube) and negative (upper tube) gelatin liquifaction.
LOWER TUBE: Staphylococcus aureus(ATCC® 25923)
UPPER TUBE: Escherichia coli (ATCC® 25922)

The organisms were grown in Nutrient Gelatin (Cat. no. Q23), incubated aerobically for 24 hours at 35ºC. The tubes were brought to room temperature in order to observe gelatin breakdown by gelatinase. A positive reaction was demonstrated by the medium remaining liquid after cooling to room temperature. A negative reaction was demonstrated by resolidification upon cooling to room temperature. An uninoculated control should be maintained during the testing process. If this tube does not resolidify during the cooling process, the test is not valid.

REFERENCES

1. Baron, E.J., L.R. Peterson and S.M. Finegold. 1994. Bailey & Scott's Diagnostic Microbiology, 10th ed. Mosby, St. Louis, MO.

2. MacFaddin, J.F. 1985. Media for Isolation, Cultivation, Identification, Maintenance of Bacteria, Vol. I. Williams & Wilkins, Baltimore, MD.

3. Howard, B.J., et al. 1997. Clinical and Pathogenic Microbiology, 2nd ed. Mosby, St. Louis, MO.

4. Isenberg, H.D. Clinical Microbiology Procedures Handbook, Vol. I, II & III. American Society for Microbiology, Washington, D.C.


ATCC is a registered trademark of the American Type Culture Collection.

012617gr