|Cat. no. Z204||ColiScreen™, 15x45mm Vial||20 tests/kit|
Hardy Diagnostics ColiScreen™ is recommended for the presumptive identification of Escherichia coli.
Hardy Diagnostics ColiScreen™ is to be used as a rapid screening test to assist in the identification of E. coli. The performance of a spot indole test alone is not an adequate screen for E. coli, since there are at least 52 species of gram-negative bacilli that grow on MacConkey, are indole-positive, and ferment lactose. The more common ones include Klebsiella oxytoca, Citrobacter freundii, C. sedlakii, C. braakii, C. koserii, C. amalonaticus, C. youngae, Aeromonas hydrophila and Serratia odorifera. The test is designed to be used on isolates demonstrating typical appearance on EMB and/or MacConkey Agar. Although most E. coli exhibit lactose-fermentation on these media, it should be noted that approximately 5% of E. coli are non-lactose-fermenters.(2) Using this test system, glucuronidase-positive, indole-positive, gram-negative organisms are presumptively identified as E. coli. Hydrolysis of the additive nitrophenyl-beta-glucopyranosiduronic acid denotes the production of glucuronidase and is detected by the development of a yellow color in the medium. Indole production is detected by addition of Kovacs Indole Reagent after the yellow color has developed. According to Thompson, approximately 96% of all E. coli strains are glucuronidase-positive.(7)
Ingredients per liter of deionized water:*
|Kovacs Indole Reagent (Cat. no. Z67, sold separately):|
|Hydrochloric Acid, 37%||250.0ml|
* Adjusted and/or supplemented as required to meet performance criteria.
STORAGE AND SHELF LIFE
Storage: Upon receipt store at 2-8ºC. Products should not be used if there are any signs of deterioration, discoloration, contamination, or if the expiration date has passed. Product is light and temperature sensitive; protect from light, excessive heat, moisture, and freezing.
Specimen Collection: This product is not intended for primary isolation of patient specimens. This product is used in conjunction with other biochemical tests to identify cultures of isolated organism.
Obtain a heavy, visible inoculum with a sterile wooden applicator stick or loop from an 18-24 hour old culture. Stab into the medium, near the glass of the tube for ease in reading. Incubate the tubes aerobically at 35ºC. for one to four hours. If the glucuronidase test is positive (the presence of a bright yellow color), test for indole. Indole production is tested by adding two to three drops of Kovacs Indole Reagent (Cat. no. Z67).
INTERPRETATION OF RESULTS
A positive glucuronidase test is indicated by the presence of a bright yellow color change. No color change is considered a negative glucuronidase test. A pink to red color developing after the addition of Kovacs Indole Reagent is indicative of a positive test. No color change on addition of this reagent is a negative test.
Presumptive identification of E. coli is indicated when both glucuronidase and indole tests are positive and the organism is gram-negative.
Organisms must be characterized as having colony morphology typical to that of Escherichia coli and must be gram-negative. Approximately 5% E. coli isolates are non-lactose-fermenters.(2)
If a colony of typical morphology has been determined to be gram-negative, both glucuronidase and indole must be positive in order to presumptively identify it as E. coli.
Although, glucuronidase- and indole-positive, some atypical strains of E. coli (E. coli group AD) are non-lactose-fermenters.
E. coli O157 appear as lactose-fermenters but are glucuronidase-negative and indole-positive.
Proper inoculation of this medium is very important. A heavy inoculum of the test organism should be taken from 18-24 hour old pure cultures of well isolated colonies.
MATERIALS REQUIRED BUT NOT PROVIDED
Standard microbiological supplies and equipment such as Kovacs Indole Reagent (Cat. no. Z67), loops, incinerators, incubators, other culture media, etc., as well as serological and biochemical reagents, are not provided.
|Test Organisms||Inoculation Method*||Incubation||Results|
|E||1-3hr||35°C||Aerobic||Glucuronidase-positive: bright yellow; Indole-positive: dark pink/red|
no color change;
Indole-negative: no color change
User Quality Control
- ColiScreen™ media should appear clear, and slightly yellowish-gray in color.
- Kovacs Indole Reagent should appear translucent with a yellow tinge and no precipitate.
Escherichi coli (ATCC® 25922) inoculum incubated in ColiScreen™ (Cat. no. Z204) medium. ColiScreen™ tube was incubated aerobically for 3 hours at 35ºC.
Klebsiella pneumoniae (ATCC® 13883) inoculum incubated in ColiScreen™ (Cat. no. Z204) medium. ColiScreen™ tube was incubated aerobically for 3 hours at 35ºC.
Escherichia coli (ATCC® 25922) inoculum incubated in ColiScreen™ (Cat. no. Z204) medium with Kovacs Indole Reagent (Cat. no. Z67, sold separately) added after incubation. ColiScreen™ tube was incubated aerobically for 3 hours at 35ºC.
Klebsiella pneumoniae (ATCC® 13883) inoculum incubated in ColiScreen™ (Cat. no. Z204) medium with Kovacs Indole Reagent (Cat. no. Z67, sold separately) added after incubation. ColiScreen™ tube was incubated aerobically for 3 hours at 35ºC.
A total 100 clinical isolates, previously identified by the Vitek® Gram-Negative ID Card, were tested and compared with another commercially available product. Isolates included: Escherichia coli (67), Escherichia coliAD (1), Escherichia coli O157 (5), Shigella sonnei (3), Enterobacter cloacae (7), Citrobacter freundii (4), Enterobacter aerogenes (5), Klebsiella oxytoca (4) Salmonella spp. (4).
Sixty-eight of the seventy-three E. coli isolates tested produced both positive glucuronidase and positive indole tests on ColiScreen™. All of the five false-negative isolates were identified as E. coli O157. It should be noted, and it is included under the "Limitations" section that, although these strains are lactose-fermenters, they are atypical because they are glucuronidase-negative. One E. coli isolate produced positive indole tests on both systems, but glucuronidase test results differed (Hardy product = positive glucuronidase; comparative product = false-negative glucuronidase).
Results of this comparison study reveal Hardy Diagnostics ColiScreen™ test to be 93% (*84.7-97.7%) sensitive. The sensitivity of the comparative product was 91.8% (*83.0-96.9%). Both devices were 100% (*87.2-100%) specific for the presumptive identification of Escherichia coli.
* 95% confidence interval as determined by the Exact Method.
1. Anderson, N.L., et al. Cumitech 3B; Quality Systems in the Clinical Microbiology Laboratory, Coordinating ed., A.S. Weissfeld. American Society for Microbiology, Washington, D.C.
2. Versalovic, J., et al. Manual of Clinical Microbiology. American Society for Microbiology, Washington, D.C.
3. Tille, P., et al. Bailey and Scott's Diagnostic Microbiology, C.V. Mosby Company, St. Louis, MO.
4. Godsey, J.H., et al. 1981. Rapid identification of Enterobacteriaceae with microbial enzyme activity profiles. J. Clin. Microbiol.; 13:483-490.
5. Isenberg, H.D. Clinical Microbiology Procedures Handbook, Vol. I, II & III. American Society for Microbiology, Washington, D.C.
6. Koneman, E.W., et al. Color Atlas and Textbook of Diagnostic Microbiology. J.B. Lippincott Company, Philadelphia, PA. E. coli serotype 0157. J. Clin. Microbiol.; 28:2165-2168.