How do you Streak a blood agar plate for identification of an unknown bacteria from a mixed culture?
Which ingredient in bile esculin media is used to inhibit gram bacteria other than Group D streptococci enterococci?
Which of the following bacterial species would be most likely to grow in bile esculin medium and hydrolyze the esculin?
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.
- Using sterile loop, pick one or two colonies from an 18-24 hours culture.
- Inoculate onto the surface of slant of bile esculin medium with an S-shaped motion.
- Incubate the inoculated tube at 35-37°C for 24 hours.
- Observe the result.
Bile Esculin Agar (BEA) is a selective differential agar used to isolate and identify members of the genus Enterococcus, formerly part of the “group D streptococci” (enterococci were reclassified in their own genus in 1984).
The addition of esculin and ferric ammonium citrate causes a darkening of the broth or agar in the presence of Listeria species (Listeria species have the ability to hydrolyze esculin, and hydrolysis of esculin turns the medium black, denoting a presumptive positive test).
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.
Bacteroides Bile Esculin (BBE) agar is an enriched, selective, and differential medium used for the isolation and presumptive identification of obligately anaerobic gram-negative bacilli of the Bacteroides fragilis group and Bilophila wadsworthia.
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.
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.
Bile–Esculin Test Inoculate the BE medium with one to three colonies and incubate it at normal atmosphere for up to 7 days. A positive reaction is recorded when a black color forms over one-half or more of the slant, or when any blackening occurs on the agar plate.
Principle of Esculin Hydrolysis Test Esculetin combines with ferric ions, generally incorporated in the medium as ferric ammonium citrate, to produce a brown-black colored compound. Alternatively, the end product glucose can be determined by detecting the change in pH resulting from its fermentation.
the presence of bile. The free esculetin reacts with ferric citrate in the medium to form a phenolic iron complex, which turns the agar slant dark brown to black. An agar slant that is more than half darkened after no more than 48 hours’ incubation is bile-esculin positive.
Esculin hydrolysis results in the production of D-glucose and esculetin. Hydrolysis can happen under acidic conditions or be catalyzed by ß-glucosidase enzyme, esculinase. Although many bacteria process esculinase, the number of bacteria that are able to hydrolyze esculin in the presence of bile is much more limited.
To detect organisms which are capable of utilizing the molecule Esculin in the presence of bile.
This medium is both selective and differential. The selective ingredients are the bile salts and the dye, crystal violet which inhibit the growth of Gram-positive bacteria.
The composition of hepatic bile is (97–98)% water, 0.7% bile salts, 0.2% bilirubin, 0.51% fats (cholesterol, fatty acids, and lecithin), and 200 meq/l inorganic salts.
It grows well on a non-selective anaerobic agar and its growth is inhibited on Bacteroides bile esculin (BBE) and kanamycin-vancomycin laked blood (KVLB) agars.
Suspend 97.0 grams in 1000 ml purified/distilled water. Dispense into bottles or tubes as desired and sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes.
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. … On chocolate agar, pneumococcal colonies are surrounded by a greenish-yellow color.
Streptococcus and Enterococcus species are catalase negative, which differentiates them from Staph- ylococcus, which is catalase positive. Streptococci have the typical gram-positive cell wall of peptidoglycan and teichoic acid and are nonmotile.
You streak your unknown bacterium onto a blood agar plate and place an optochin disc on the surface of the plate. After 24 hours, your plate looks like this. Is the unknown bacterium sensitive or resistant to optochin?
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.
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.
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.
Bile esculin agar contains oxgall (bile salts) to inhibit the growth of gram positive organisms other than enterococci and group D streptococci.
Interpretation of Results 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.
coli and assessed the ability of colonies in a population to hydrolyze esculin with and without preincubation in inducible substrates at 24, 48, and 72 h. … coli strain was able to produce constitutive enzyme; preincubation in esculin and salicin resulted in an induction of the beta-glucosidase.