VLD 421: Veterinary Clinical Biochemistry and Laboratory Diagnosis-II (0+1)

ESCULIN HYDROLYSIS TEST

Principle

• Esculin medium without bile is useful in differentiating several species of non-fermenting bacilli.
• Esculin is a substituted glucoside that can be hydrolysed by certain bacteria to yield glucose and esculetin. Esculin is a fluorescent compound that floureses, under long wave UV light at 360 nm.
• When esculin is hydrolysed, fluorescence is lost, and the medium turns black due to the reaction of esculin with the ferric ions in the medium.

Methodology

• Inoculate the test organism in Aesculin broth ( Aesculin 1 g+ ferric citrate 0.5 g in 1000 ml of peptone water).
• Incubate at 37^ºC for upto 7 days.
• Examine for blackening and under the ultraviolet rays (360nm)

Result

• The development of black colour or the loss of fluorescence under UV light (360 nm) is interpreted as a positive test.
• Fluorescence or lack of black colour is interpreted as a negative test.

Quality control

• Positive    : Streptococcus faecalis
• Negative  : Streptococcus agalactiae