for the rest of experiments Medgar Evers Colinge, CUNY tly from green to correct
ID: 216110 • Letter: F
Question
for the rest of experiments Medgar Evers Colinge, CUNY tly from green to correct Please e choose the t 1 After performing the O/y heop hacose test, which organism displayed a color change vellow on both the aerobic and anderobic tube? al Ecl and neutral end product fermentation test is called a) MR-VP b Nutrient broth c) Nutrient agar should d) Urea agar To detect the presence of mixed acids during fermentation, 5 drops of be added to the media and a red coloration should be observed 3. a) Iron chloride b) Kovac's reagent c) Methyl red d) Hydrogen peroxide 4 The pht indicator found in the specific sugar fermentation tubes is When an organism ferments that particular sugar, the media turns from red to a) Litmus paper; orange b) Benedict's reagent; red Phenol red; yellow Kovac's reagent; purple c) d) S- Usually when an organism such as E.colí is positive for mixed acid fermentation, it is negative for a) Neutral end product fermentation b) Citrate fermentation c) Oxidase test d) Nitrate reductionExplanation / Answer
1.After performing the O/F glucose test,which organism displayed a color change from green to yellow on both the aerobic and anerobic tube:E.coli
The Oxidative-fermentative(OF)test is to differentiate between oxidative bacteria (that produces the acid from carbohydrates under aerobic condition only)and fermentative bacteria(that produces acid both under aerobic and anerobic conditions).The higher concentration of acid produced during fermentation will turn the bromthymol blue indicator in OF media from green to yellow in the presence or absence of oxygen.
Fermentative result:Acid production on both(open and covered) tubes.The acid produces changes the pH indicator,bromthymol blue,from green to yellow.
Ex:Escherichia coli
2.The media used for mixed acid and neutral end product feremntation test is called :MR-VP
Methyl Red(MR) and Voges-Proskauer(VP)broth is used as a part of the IMViC tests as the medium in which both the Methyl red and Voges-Prosakuer tests can be performed.It is a simple broth that contains peptone,buffers and dextrose or glucose.
Different bacteria convert dextrose and glucose to pyruvate using different metabolic pathways.Some of these pathways produce unstable acidic products which quickly convert to neutral compounds.Some organisms use the butylene glycol pathway ,which produce neutral end products ,including acetoin and 2,3-butanediol.Other organisms use the mixed acid pathway,which produce acidic end products such as lactic,acetic and formic acid.
3.To detect the presence of mixed acid during fermentation ,5 drops of Methyl Red should be added to the media and a red coloration should be observed
this is applied in combination with Voges-Proskaur test.Here Methyl red is pH indicator.Changes color at pH below 4.5 which occurs when bacteria produce acid end products from fermentation.It indicates use of mixed acid fermentation pathway.Red coloration at pH 4.4 or below indicates the presence of mixed acid fermentation products.Shows yellow at pH of 6.2 and above which shows acid has not been produced.
4.The pH indicator found in the specific sugar fermentation tubes is phenol red.when an organism ferments that particular sugar ,the media turns from red to yellow.
The carbohydrate fermentation test is used to determine whether or not bacteria can ferment a specific carbohydrate.
Basal medium containing a single carbohydrate source such as glucose,Lactose,Sucrose or any other carbohydrate is used for this purpose.The pH indicator will detect the lowering of the pH of the medium due to acid production.Small inverted tube called Durham tube is also immersed in the medium to test for the production of the gas.(Hydrogen or Carbon dioxide)
Phenol red iscommonly used as a pH indicator in carbohydrate fermentation tests.Other pH indicator indicators such as bromocresol/bromocresol purple(BCP),bromothymol/bromothymol blue(BTB) and Andrade's can be used.
After incubation the liquid in the tube turns yellow (indicated by the change in color of the phenol red indicator).It indicates that there is drop in the pH because of the production of the acid by the fermentation of the carbohydrate(sugar) present in the media.
5.Usually when an organism such as E.coli is positive for mixed acid fermentaion,it is negative for :Neutral end product fermentation.
Certain bacteria produce neutral reacting end products when cultivated in specific media.Particularenteric bacteria that ferment glucose,further metabolize pyruvic acid to formacetyl-methyl carbinol(acetoin).This end product in the presence of atmospheric oxygenand 40% potassium hydroxide is converted to diacetyl.Diacetyl,under catalytic action of alpha-naphthol and creatine,is converted into red complex.This is positive VP test reaction.
The E.coli is VP negative.The Vp testis used primarilyto separate Escherichia coli from VP positive groups.(Klebsiella-Enterobacter group).
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