The carbohydrate fermentation test is supplied to determine whether or not bacteria deserve to ferment a details carbohydrate. Carbohydrate fermentation fads are useful in differentiating among bacterial teams or species.It tests because that the existence of acid and/or gas produced from carbohydrate fermentation. Basal tool containing a single carbohydrate resource such together glucose, lactose, sucrose or any kind of other carbohydrate is used for this purpose. A pH indicator (such together Andrade’s solution, bromcresol violet (BCP), bromothymol blue (BTB) or phenol red) is additionally present in the medium; which will certainly detect the lowering of the pH that the medium as result of acid production. Tiny inverted tubes dubbed Durham tube is likewise immersed in the tool to test for the production of the gas (hydrogen or carbon dioxide).The term fermentation is often used to describe the breaking down or catabolism of a carbohydrate under anaerobic conditions. Therefore, bacteria capable of fermenting a carbohydrate space usually facultative anaerobes.

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Contents1 supplies of Carbohydrate Fermentation Test 2 Principle3 test procedure3.1 Preparation and Composition of the media 3.2 A. Preparation of the media 3.3 B.Inoculation and Incubation3.4 C.Interpretation that the results 

Uses that Carbohydrate Fermentation Test 

Carbohydrate fermentation patterns have the right to be used to differentiate amongst bacterial groups or species.All members the Enterobacteriaceae family are glucose fermenters (they deserve to metabolize glucose anaerobically).Maltose fermentation differentiates Proteus vulgaris (positive) indigenous Proteus mirabilis (negative).Both Neisseria gonorrhoeae (gonococci) and Neisseria meningitides (meningococci) ferments glucose, however only meningococci ferments maltose.Rapid carbohydrate utilization tests (RCUTs) have the right to be perform to identification Corynebacterium diphtheriae and other Corynebacterium species.You might like “Differences between Neisseria gonorrhoeae (gonococci) and Neisseria meningitides (meningococci)”


When microorganisms ferment carbohydrate an acid or acid v gas are produced. Depending upon the organisms involved and the substrate being fermented, the end assets may vary. Usual end-products of bacterial fermentation encompass lactic acid, formic acid, acetic acid, butyric acid, butyl alcohol, acetone, ethyl alcohol, carbon dioxide, and also hydrogen.The production of the acid lowers the pH of the check medium, i m sorry is recognize by the color adjust of the pH indicator. Color adjust only wake up when sufficient amount of mountain is produced, together bacteria may utilize the peptone producing alkaline by-products.
Common pH indicators for Carbohydrate Fermentation Media (Source: ASMCUE)
Phenol red is commonly used together a pH indicator in carbohydrate fermentation tests. Various other pH indicators such together bromocresol/bromocresol purple (BCP), bromothymol/bromothymol blue (BTB), and also Andrade’s have the right to be used.Durham pipe are inserted upside under in the check tubes come detect gas production. If the test organisms produce gas, the gas displaces the media present inside the tube and gets trapped developing a clearly shows air bubble.Based on the characteristics reactions observed, bacteria have the right to be classified as:Fermenter with acid manufacturing onlyFermenter v acid and gas productionNon-fermenter

Test procedure

Phenol red carbohydrate broth is generally used in carbohydrate fermentation tests. The carbohydrate sources can vary based upon your test requirements.Common broth media are:Phenol red glucose brothPhenol red lactose brothPhenol red maltose brothPhenol red mannitol brothPhenol red sucrose broth

Preparation and Composition of the media 

Get specific phenol red carbohydrate check media indigenous the commercial providers or phenol red broth base and also add details carbohydrate resource based on your test requirements, or you have the right to prepare media mix the following ingredients.Composition the Phenol Red Carbohydrate BrothTrypticase or protease peptone No. 3: 10 gSodium chloride (NaCl): 5 gBeef extract (optional): 1 gPhenol red (7.2 ml of 0.25% phenol red solution): 0.018 gCarbohydrate source: 10 g

A. Ready of the media 

Prepare broth media by mixing every ingredients in 1000 mL of distilled/deionized water and also heating gently to dissolve it (Note: use a single carbohydrate source based on your requirements).Fill 13 x 100 mm check tubes through 4-5 ml that phenol red carbohydrate broth.Insert a Durham tube to detect gas production.Autoclave the prepared test media (at 121°C for 15 minutes) to sterilize. The sterilization process will likewise drive the broth right into the reverse Durham tube. (Note: as soon as using arabinose, lactose, maltose, salicin, sucrose, trehalose, or xylose, autoclave at 121°C for only 3 minutes as these carbohydrates are subject to break down by autoclaving)The prepared broth media will certainly be a light red color and the final pH must be 7.4 ± 0.2.Alternatively, prepare phenol red broth base, warm sterilize and also cool to 45°C. Prepare details carbohydrate solution separately, filter the equipment using membrane filter (pore size: 0.45 μm). Add carbohydrate systems to the broth base and mix it. The wanted carbohydrate concentration is 1%.

B.Inoculation and Incubation

Aseptically inoculate each test tube with the test pathogen using one inoculating needle or loop. Alternatively, inoculate each test tube through 1-2 drops of an 18- to 24-hour brain-heart infusion broth society of the desired organism .Incubate tubes in ~ 35-37°C because that 18-24 hours. Much longer incubation periods might be required to check a an unfavorable result.

C.Interpretation the the results 

Image source: ASMCUE
Acid production:Positive: After incubation the fluid in the tube transforms yellow (indicated through the adjust in the color of the phenol red indicator). It suggests that there is autumn in the pH due to the fact that of the production of the mountain by the fermentation the the carbohydrate (sugar) current in the media.NOTE:*If you space using various other pH indicators please describe Table 1 for their corresponding colors in certain pH.Negative: The tube containing medium will stay red, denote the bacteria can not ferment that particular carbohydrate source present in the media.Gas ProductionPositive: A balloon (small or large depending up the quantity of gas produced) will certainly be seen in the turning back Durham tube.

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Negative: There won’t be any bubble in the reverse Durham pipe i.e. Bacteria go not create gas indigenous the fermentation the that details carbohydrate current in the media i.e. Anaerogenic organisms.References and also further readingsCarbohydrate Fermentation Protocol through Microbe Library