Aesculin splitting

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The Äskulinspaltung , also known as Äskulinhydrolyse (or Esculin hydrolysis ), is in the microbiological diagnosis used bacterial species , in particular from the group of fermenters , to distinguish from each other.

principle

Aesculetin iron complex

Some types of bacteria , mostly from the nonfermenter group , are able to hydrolytically split esculin into glucose and esculetin with the β-glucosidase they produce . The aesculetin forms a black complex compound with the iron (III) ions of the test solution added later, which indicates a positive reaction.

Test execution

About 1 to 3 colonies of the bacterium to be examined are inoculated into the aesculin broth from a solid nutrient medium (agar plate / primary culture) using a sterile inoculating loop . The suspension culture is then incubated for about 16 to 24 hours at 36 ± 1 ° C. After the incubation , about 5 drops of an iron (III) chloride solution are added to the broth.

The addition step is not necessary if an Aeskulin agar medium containing iron (III) chloride is kept in stock as a slant in test tubes as a finished test. With these, the test result can be read off directly after cultivation; If the reaction is positive, the agar slant in the tube turns black.

Evaluation of the test

Positive: the bouillon
turns black. Negative: no black coloration

Aesculin-positive bacterial species Aesculin-negative bacterial species
Stenotrophomonas maltophilia Pseudomonas aeruginosa
Enterococcus faecalis Streptococcus agalactiae
Pseudomonas luteola Enterobacter cloacae
Sphingomonas paucimobilis

Working equipment, reagents, culture media

  • Aesculin broth
  • 10% iron (III) chloride solution

literature

  • SA Waitkins: Evaluation of rapid methods of identifying group B streptococci. In: Journal of clinical pathology. Volume 33, Number 3, March 1980, pp. 302-305, ISSN  0021-9746 . PMID 6991531 . PMC 1146056 (free full text).
  • JG Barr, RJ Mahood: Complementary use of aesculin hydrolysis and inositol fermentation in the characterization of Klebsielleae. In: Journal of clinical pathology. Volume 30, Number 1, January 1977, pp. 45-49, ISSN  0021-9746 . PMID 320229 . PMC 476636 (free full text).

Individual evidence

  1. ↑ G. Colman: The classification of streptococcal strains. (1970). Ph.D. Thesis, University of London.