BIOL2420 Lone Star College Montgomery Bile Esculin Lab Report PDF

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Summary

Bile esculin, enterococci, hydrolysis, formation of glucose, non enterococcus group...

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SARAH GILDENBERG

LONE STAR COLLEGE - MONTGOMERY

BIOL 2420 - SPRING 2020

Microbiology Lab Notebook Report

Bile Esculin - Handout March 19, 2020

Introduction Bile-esculin test is widely used to differentiate Enterococci and Non-enterococcus group D streptococci, which are bile tolerant and can hydrolyze esculin to esculetin, from non-group D viridans group streptococci, which grow poorly on bile. It is a low cost, rapid test with good sensitivity and specificity. Bile-esculin test is based on the ability of certain bacteria, notably the group D streptococci and Enterococcus species, to hydrolyze esculin in the presence of bile (4% bile salts or 40% bile).

Purpose Bacteria that are bile-esculin positive are, first of all, able to grow in the presence of bile salts. Hydrolysis of the esculin in the medium results in the formation of glucose and a compound called esculetin.

Materials • •

Bile-esculin agar medium is prepared as agar slants or plates. The constituent of Bile-esculin agar medium are: • Peptone • Beef extract • Oxgall (Bile) • Esculin • Ferric citrate • Agar • Bile esculin medium contains esculin and peptone for nutrition and bile to inhibit Grampositive bacteria other than Group D streptococci and enterococci. • Ferric citrate is added as a color indicator.

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SARAH GILDENBERG

LONE STAR COLLEGE - MONTGOMERY

BIOL 2420 - SPRING 2020

Procedure 1. Inoculate one BE slant with each organism. 2. Inoculate one nutrient agar control with each organism. 3. Incubate slant tubes for 24-48 hours. 4. A positive test is darkening of at least 1/2 of the agar.

Results

- Darkening of the medium, blackening of the medium (within 48 hours) - Medium is darkened within 48 hours indicates that the organism hydrolyzes esculin in the presence of bile; presumptive identification as a member of Group D Streptococcus or Enterococcus. - No darkening of the medium after 48 hours means that the organism does not hydrolyze esculin in the presence of bile. Presumptive identification as a non-Group D Streptococcus or Enterococcus.

Conclusion When esculin is hydrolyzed in BEA, the resulting esculetin reacts with ferric ions in the medium to produce a dark brown/ black precipitate, which darkens the medium surrounding the growth.

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