What does a negative bile esculin test mean?

A negative test result also occurs in the bile-esculin medium if the organism cannot grow in the presence of bile, regardless of the ability to hydrolyze esculin. A positive disk test is indicated by the development of a dark brown or black color. A negative disk test remains colorless.

What does a positive bile esculin test mean?

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

What does a negative bile esculin test look like?

Streptococcus pyogenes does not hydrolyze esculin in the presence of bile. No dark brown complex is formed. This is a negative result.

What does it mean when the bile esculin agar turns black?

If an organism can hydrolyze esculin in the presence of bile, the product esculetin is formed. Esculetin reacts with ferric citrate (in the medium), forming a phenolic iron complex which turns the entire slant dark brown to black.

How long must a bile esculin agar plate be incubated before a negative result can be recorded?

Negative test. Inoculate 3 of each decarboxylase broth and have 1 control of each. Overlay tubes with sterile mineral oil. Incubate for one week.

What Streptococcus are bile-esculin positive?

All strains of S. bovis and approximately 10% of viridans streptococci are bile-esculin positive.

How do you make a bile solution?

Bile salt can be prepared by adding 10 grams of sodium desoxycholate in 100 ml distilled water. The solution should then be dispensed in small amounts to minimize contamination. The shelf life of the solution is usually 270 days. The storage should be done at 15 to 30°C.

How can you tell the difference between staphylococcus and Streptococcus?

Streptococci are Gram-positive cocci that grow in pairs or chains. They are readily distinguished from staphylococci by their Gram-stain appearance and by a negative catalase test.

What does PYR negative mean?

Negative: No color change or a blue color due to a positive indole reaction. Examples: Group B Streptococci (Streptococcus agalactiae), Streptococcus mitis, S.

How do you know if you have Streptococcus Viridans?

Identification. Viridans streptococci can be differentiated from Streptococcus pneumoniae using an optochin test, as viridans streptococci are optochin-resistant; they also lack either the polysaccharide-based capsule typical of S. pneumoniae or the Lancefield antigens of the pyogenic members of the genus.

How do you interpret bile esculin test results?

Result Interpretation of Bile Esculin Test A positive tube test in medium containing ferric ammonium citrate is indicated by the blackening of the medium. A negative tube test is indicated by a lack of color change. The medium will fluoresce under UV light (366 nm).

What is bile esculin positive bacteria?

Bacteria that are bile-esculin positive are able to grow in the presence of bile salts and the hydrolysis of the esculin in the medium results in the formation of glucose and a compound called esculetin. Esculetin, in turn, reacts with ferric ions (supplied by the inorganic medium component ferric citrate) to form a black diffusible complex.

What is the significance of hydrolysis of esculin and bile?

Thus the tolerance to the presence of bile and the hydrolysis of esculin provide the means to presumptively identify organisms. If an organism can hydrolyze esculin, the media will turn dark brown or black.

What happens if the inoculum is too high on Bile Esculin Agar?

If the inoculum is too great or the concentration of bile is less than 40%, viridans group streptococci other than S.bovis can give a positive reaction on bile-esculin agar. A heavy inoculum on BEA may cause interpretation of the bile esculin test difficult to read.