How is bile esculin differential?

The differential ingredient is esculin. 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.

What makes bile-esculin media selective and differential?

Bile esculin agar is both selective and differential medium. The selective aspect of the bile esculin agar is sodium azide and oxagall which inhibit the growth of G- and most G+. The differential aspect of esculin agar is esculin which very few organisms can hydrolyze in the presence of bile.

How does a bile-esculin test work?

The bile esculin test selects organisms first on the basis of their ability to grow in a medium with 4% bile salts followed by the selection based on their ability to hydrolyze esculin. The hydrolysis of esculin results in glucose and a compound called esculetin.

What organisms does the bile-esculin test differentiate between?

The bile-esculin test is widely used to differentiate enterococci and 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.

What is the purpose of bile esculin agar?

Uses. Bile Esculin Agar is used primarily to differentiate Enterococcus from Streptococcus. Members of the genus Enterococcus are capable of growing in the presence of 40% bile (oxgall) and hydrolyzing esculin to glucose and esculetin. Esculetin combines with ferric ions to produce a black complex.

How do you set up bile esculin agar?

Preparation of Use of Bile Esculin Agar

  1. Suspend 64.5 grams in 1000 ml distilled water.
  2. Heat to boiling to dissolve the medium completely.
  3. Dispense into tubes or flasks.
  4. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes.

How does bile in bile-esculin medium contribute to the isolation and presumptive identification of Enterococcus?

Organisms capable of growth in the presence of 4% bile and able to hydrolyze esculin to esculetin. Esculetin reacts with Fe3+ and forms a dark brown to black precipitate. Thus the tolerance to the presence of bile and the hydrolysis of esculin provide the means to presumptively identify organisms.

How does Esculin hydrolysis work?

Principle of Esculin Hydrolysis Test

Esculin hydrolysis is commonly determined by detecting the end product esculetin. Esculetin combines with ferric ions, generally incorporated in the medium as ferric ammonium citrate, to produce a brown-black colored compound.

What is the purpose of using bile esculin agar with vancomycin?


Remel Bile Esculin Azide Agar w/ 6 µg/ml Vancomycin is a solid medium recommended for use in qualitative procedures as a screening method for primary isolation and presumptive identification of vancomycin-resistant enterococci (VRE) from surveillance cultures.

What is the indicator in the bile-esculin test?

Bile esculin medium contains esculin and peptone for nutrition and bile to inhibit Gram-positive bacteria other than Group D streptococci and enterococci. Ferric citrate is added as a color indicator.

How can you tell the difference between streptococcus and Enterococcus?

It is generally accepted that the enterococci and the non-enterococcal group D streptococci have the same LTA antigen which cross-reacts. The only recognized difference is that the non- enterococcal species contain relatively small amounts of the antigen.

Does Streptococcus pneumoniae grow on bile esculin agar?

S pneumoniae are non-beta-hemolytic streptococci that are optochin-positive, bile-soluble, and bile esculin-negative. In liquid media, S pneumoniae replicates in chains.

What Streptococcus are bile-esculin positive?

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

What is the purpose of the bile in the medium?

bile, also called gall, greenish yellow secretion that is produced in the liver and passed to the gallbladder for concentration, storage, or transport into the first region of the small intestine, the duodenum. Its function is to aid in the digestion of fats in the duodenum.

What does bile juice do?

Bile is a fluid that is made and released by the liver and stored in the gallbladder. Bile helps with digestion. It breaks down fats into fatty acids, which can be taken into the body by the digestive tract.

How do you perform a bile esculin agar test?

A. Tube Test

  1. Using sterile loop, pick one or two colonies from an 18-24 hours culture.
  2. Inoculate onto the surface of slant of bile esculin medium with an S-shaped motion.
  3. Incubate the inoculated tube at 35-37°C for 24 hours.
  4. Observe the result.

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.

What is hippurate hydrolysis?

Hippurate hydrolysis test is used to detect the ability of bacteria to hydrolyse substrate hippurate into glycine and benzoic acid by action of hippuricase enzyme present in bacteria. Hippuricase is a constitutive enzyme that hydrolyzes the substrate hippurate to produce the amino acid glycine.

What is the role of oxgall in bile esculin agar and how does it work?

Bile (oxgall) is the selective agent added to separate Group D streptococci (the Streptococcus bovis group and enterococci) from other non-Group D streptococci. iv. Ferric citrate is added as a source of oxidized iron to indicate a positive test.

Which of the following bacterial species would be most likely to grow in bile-esculin medium and hydrolyze the esculin?

Characteristically, group D streptococci and enterococci grow in the presence of bile and hydrolyze esculin. On Bile Esculin Agar, typical group D streptococci and enterococci colonies appear as small transparent colonies with brown- black halos.

What does bile soluble mean?

Last updated: June 14, 2019 by Sagar Aryal. Bile Solubility Test is the test which differentiate Streptococcus pneumoniae (positive- soluble) from alpha-hemolytic streptococci (negative- insoluble). Streptococcus pneumoniae is bile soluble whereas all other alpha-hemolytic streptococci are bile resistant.

What is the application purpose of bile esculin agar what organisms does it select for and how are these organisms further differentiated )?

Bile esculin agar (we do not use bile esculin azide agar, as sodium azide is extremely hazardous) is a selective and differential medium which is used to presumptively identify enterococci and group D streptococci based on the ability of an organism to hydrolyze esculin.

Is blood agar selective or differential?

Blood agar is differential media because 3 different types of hemolysis, or lysing of red blood cells, can be seen on this plate.

Is catalase test selective or differential?

As a differential test, the catalase test is used to distinguish between streptococci (catalase negative) and staphylococci (catalase positive). Coagulase acts within host tissues to convert fibrinogen to thrombin.

Is Enterococcus bile resistant?

Enterococcus faecium is a Gram-positive commensal bacterium of the mammalian intestinal tract. In the last two decades it has also emerged as a multi-resistant nosocomial pathogen. In order to survive in and colonize the human intestinal tract E. faecium must resist the deleterious actions of bile.

How do you identify Enterococcus?

Presumptive identification: Growth on bile esculin agar and in 6.5% salt broth are two characteristics that have commonly been used to identify Enterococcus species to the genus level. A positive esculin in combination with a positive PYR reaction is another approach to presumptive identification.

Are Enterococcus encapsulated?

Three strains of encapsulated Enterococcus faecalis, which produced highly mucoid coalescing colonies on routine bacteriologic media, were isolated from urine specimens of patients with urinary tract infection. Encapsulation could be demonstrated through India ink preparations.

Is Enterococcus alpha hemolytic?

Classification: There are a number of different classification systems for streptococci and enterococci. The most commonly used, because of its simplicity, is the hemolytic pattern of the different species — alpha (green hemolysis), beta (clear lysis) and gamma (no hemolysis) on blood agar plates.

Why was S. pneumoniae incubated in a candle jar?

Isolation on Blood agar

Pneumococci frequently require enriched media and increased CO2 tension for initial isolation. They are usually isolated on Blood agar and incubated in a candle jar (a closed container in which a lit candle is placed to remove O2 and increase CO2 ) at 37C.

Is Streptococcus pneumoniae aerobic or anaerobic?

Streptococcus pneumoniae are lancet-shaped, gram-positive, facultative anaerobic bacteria with more than 100 known serotypes.

What is the optochin test used for?

This test determines whether the bacterium is either sensitive (susceptible) to optochin or resistant to the chemical. The optochin test is widely used in the form of filter paper discs, impregnated with ethylhydrocupreine hydrochloride, which are applied directly to inoculated plates before incubation.

Is enterococci gram-positive or negative?

Enterococci are Gram-positive facultative anaerobic cocci in short and medium chains, which cause difficult to treat infections in the nosocomial setting. They are a common cause of UTI, bacteremia, and infective endocarditis and rarely cause intra-abdominal infections and meningitis.

What bacteria are PYR positive?

Positive results were uniformly obtained for the PYR test with the following species: Citrobacter spp, Klebsiella spp, Enterobacter aerogenes, Enterobacter agglomerans group, Serratia marcescens and S. odorifera. On the other hand, negative results were uniformly displayed by E. coli (including inactive E.

What are the three functions of bile?

It aids in digestion, absorption, excretion, hormone metabolism and other functions. Bile juice is a digestive fluid produced by the liver. It is stored and concentrated in the gallbladder. Its main function is to convert fats in food into fatty acids, which are absorbed in the gut.

What stimulates the production of bile?

When stimulated by the hormone cholecystokinin (CCK), the gallbladder contracts, pushing bile through the cystic duct and into the common bile duct. Simultaneously, the sphincter of Oddi relaxes, permitting bile to enter the duodenal lumen.

Is bile a poop?

Stool color is generally influenced by what you eat as well as by the amount of bile — a yellow-green fluid that digests fats — in your stool. As bile pigments travel through your gastrointestinal tract, they are chemically altered by enzymes, changing the pigments from green to brown.

How bile is produced?

Bile is a liquid produced by your liver and stored in your gallbladder. When prompted by hormones and the vagus nerve, bile is released from your gallbladder into your duodenum and intestines. Your body then uses it to break down fats, absorb vitamins, and remove wastes that your body doesn’t need.

Is bile acidic or basic?

The normal liver bile, out of which it tends to precipitate, is alkaline, with an average pH of 8.20 but in the gall bladder where conditions might otherwise seem especially favorable to precipitation, the secretion undergoes a change toward the acid side, becoming on long sojourn there, strongly acid to litmus (pH …

What is the role of bile salts during digestion process?

Bile is a greenish-yellow fluid made by the liver and stored in our gallbladder. Bile salts help with the digestion of fats in our bodies. They also help us to absorb fat-soluble vitamins like A, D, E, and K.