TCBS agar

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The TCBS agar is a nutrient medium for the isolation and selective cultivation of bacteria of the genus Vibrio , such as. B. the causative agent of cholera - Vibrio cholerae - and other vibrions that cause vomiting and diarrhea ( gastroenteritis ), such as Vibrio parahaemolyticus or the so-called NAG vibrions (non-agglutinating vibrions), which are non-O1 strains is about Vibrio cholerae .

TCBS agar stands for T hiosulfate C itrate B ile (Salts) S ucrose agar and highlighting the main components of the culture medium: sodium thiosulfate , sodium citrate , bile salts (in English bile for bile) and sucrose (in English sucrose ). The recipe originally published in 1962 by the Japanese Y. Nakanishi was modified a year later by T. Kobayashi.

Areas of application

This medium is recommended by the American Public Health Association for the microbiological examination of food. Furthermore, the test methods used in food microbiology for Vibrio cholerae and other Vibrio species are certified by ISO 21872 and in the USA by the Bacteriological Analytical Manual (BAM) of the Food and Drug Administration (FDA) - the US Food and Drug Administration Drug Safety - Mandatory and also recommends the use of TCBS agar.

In the case of samples such as water or food, the vibrions are first concentrated in alkaline peptone water. This nutrient broth has a high concentration of sodium chloride and an alkaline pH value of 8.5; these two parameters inhibit the growth of numerous other bacteria. If the cultivation takes place in this medium at 42 ° C, the enrichment is even more selective, since the growth of other mesophilic bacteria is inhibited by the high temperature . To isolate Vibrio species, a small volume of the nutrient broth is plated out on TCBS agar after the enrichment. For clinical specimens such as B. stool samples or vomit these can be spread with a swab on the nutrient medium. In addition to the selective medium TCBS agar, a nutrient medium that is not very selective should also be inoculated.

Mode of action

Yellow colored colonies of Vibrio cholerae on TCBS agar

TCBS agar stands for Thiosulfate Citrate Bile (Salts) Sucrose Agar and refers to the most important components of the nutrient medium: High concentrations of sodium thiosulfate and sodium citrate largely inhibit the growth of gram-negative Enterobacteriaceae , which are also present in stool samples, for example. Ox bile (in English bile ) and sodium cholate (the sodium salt of cholic acid , a bile acid ) prevent the growth of the gram-positive accompanying flora, v. a. the enterococci . Sucrose (in English sucrose ) is the only carbohydrate in TCBS agar and restricts the growth of bacteria, which can not utilize sucrose. Together with the included pH indicators thymol blue and bromothymol blue , the breakdown of carbohydrates by Vibrio species can be made visible through acid formation, the color of the pH indicators changing from blue (alkaline pH value) to yellow (acidic pH value) .

If not inoculated, the medium has an alkaline pH value (pH 8.6), which also inhibits the growth of other bacteria. It is colored blue-green due to the pH indicators it contains. The Vibrios to be isolated with the TCBS agar are halophilic ("salt-loving"), so they can be cultivated in or on nutrient media with increased salt concentration so that the high concentration of sodium chloride and other salts in the medium does not impair their growth.

evaluation

The Petri dishes with the inoculated TCBS agar are incubated for 18 to 24 hours at 35 ° C. under aerobic conditions . Vibrio cholerae forms flat, yellow, 2 to 3 mm colonies on the nutrient medium , Vibrio alginolyticus large, yellow colonies, and the medium around the colonies is also colored yellow due to the acid formation. V. parahaemolyticus, however, forms smaller colonies with a blue-green center.

In addition to the Vibrions, there are only a few Proteus strains that can utilize sucrose with the formation of acid and form colonies similar to those of Vibrio species. However, like other bacteria from the Enterobacteriaceae family, they are inhibited by other ingredients in the nutrient medium and therefore show only weak growth or no growth at all. Bacteria from the genus Pseudomonas also only grow in an inhibited manner and can also be distinguished from Vibrions by the blue colony color, as they cannot utilize sucrose with acid formation. Colonies grown on TCBS agar have to be examined further to confirm and differentiate the different Vibrio species, for example by means of biochemical tests from a "colorful series" ; the assignment to the serotypes of Vibrio cholerae can be made by means of an agglutination test.

Typical composition

The nutrient medium usually consists of (data in grams per liter ):

See also

Individual evidence

  1. ↑ a b Profiles of rare and imported infectious diseases. (No longer available online.) In: Website of the Robert Koch Institute (RKI). Archived from the original on December 30, 2013 ; Retrieved March 4, 2013 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.rki.de
  2. ↑ a b Herbert Hof, Rüdiger Dörries: Dual Series: Medical Microbiology. 3. Edition. Thieme Verlag, Stuttgart 2005, ISBN 978-3-13-125313-2 .
  3. ↑ a b c d e Charles A. Kaysner, Angelo DePaola, Jr .: Bacteriological Analytical Manual, chapter 9: Vibrio. In: Website of the Food and Drug Administration (FDA). Retrieved March 18, 2013 .
  4. ↑ a b c d e f Technical information on TCBS agar (Vibrio selective agar). on the website of Merck KGaA , accessed on March 18, 2013 .
  5. ↑ Don F. Splittstoesser (Ed.): Compendium of Methods for the Microbiological Examination of Foods . 3. Edition. American Public Health Association 1992, ISBN 0875531733 .
  6. ↑ a b Rapid testing solutions for the detection of Vibrio cholerae. (No longer available online.) On the Merck KGaA website , formerly in the original ; Retrieved March 18, 2013 .  ( Page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Toter Link / www.merckmillipore.de  
  7. ↑ Technical information Alkaline Peptone Water. on the website of Merck KGaA , accessed on March 4, 2013 .
  8. ↑ F. Burkhardt: The bacteriological diagnosis of the Vibrio EI Tor infection. In: Zentralblatt für Bakteriologie, Parasitenkunde, Infectious Diseases and Hygiene. 1. Dept. of medical-hygienic bacteriology, virus research and parasitology. Originals. Volume 212, Number 1, December 1969, pp. 177-189, ISSN  0372-8110 . PMID 4195371 .