GELATIN STRIPS K250

DISCUSSION:

The enzyme gelatinase, which liquifies gelatin, is one of these. This enzyme is produced by only a few members of Enterobacteraciae, primarily Serratia sp., Proteus mirabilis, Proteus vulgaris, and some Enterobacter species. Salmonella and Shigella are negative with the exception of Sal. arizona. The gelatin test may also be used in the I.D. of organisms other than Enterobacteraciae, specifically in differentiating the Pseudomonas species or anaerobes. Key Gelatin Strips indicate production of gelatinase by the visibility of the blue color of the base material when the gelatin has been liquified from a strip incubated in a heavy suspension of the organism being tested.

MATERIAL SAFETY:

KEY Gelatin strips contain an emulsion of gelatin bonded to an acetate base. These strips are chemically inert and contain no hazardous or toxic material. No action or treatment is required on contact or ingestion. The acetate base is combustable and should not be used around an open flame.

MATERIALS REQUIRED:

Key Gelatin Strips are sold in bottles of 50. Usage requires preliminary growth on media appropriate for the specimen. Consult a reference manual such as the Manual of Clinical Microbiology for appropriate media. The following items are required but not provided: small test tubes (e.g. 10 x 75), loop for harvesting colonies, and distilled water.

STORAGE

Store tightly covered in a cool, dry place

INSTRUCTIONS:

1) In a small test tube, make a heavy suspension of the organism to be tested in 0.5 to 1 ml. of distilled water.

2) Drop 1 gelatin strip in the test tube. Alternately, if you already have a pure culture in broth, you may drop the gelatin strip directly into that tube (e.g. TSB).

3) Incubate at 37 degrees for up to 72 hours. Some liquification may be seen as quickly as 30-60 minutes, appearing first as a pale ring on the surface of the liquid with clearing on the sides of the strip.

INTERPRETATION:

A positive result is the melting of the gelatin exposing the clear base material.

QUALITY CONTROL

A gelatinase positive organism should be tested along with each test group. Discard used tests in a manner conforming with accepted laboratory procedures for biohazardous materials. We recommend Proteus vulgaris ATCC 8427 as positive and E. coli ATCC 25922 as negative.

FREQUENTLY ENCOUNTERED GELATINASE POSITIVE BACILLI

Fermenters:

Proteus vulgaris 91%

Proteus mirabilis 90%

Proteus myxofaciens 100%

Serratia marsescens 90%

Serratia liquifaciens 90%

Serratia odorifera 95%

Nonfermenters:

Pseudomonas stutzeri 100%

Pseudomonas flourescens90%

Pseudomonas cepacia 90%

REFERENCES

1)Bailey and Scott's Diagnostic Microbiology, 7th Edition, 1986, pg. 418

(2)Manual of Clinical Microbiology, 5th Edition, Chapters 40 & 41.

(3)Nonfermentative Gram Negative Bacilli, a syllabus for detection and identification, by M.J. Pickett.

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