1. Monosaccharide Fermentation Test
(1) Experimental Principle
This test is used to determine whether bacteria can ferment specific monosaccharides such as glucose, lactose, or maltose. Each sugar is added to a peptone water medium at a final concentration of 0.75–1%. A small inverted tube and phenol red indicator are also included in the medium. After inoculating the bacterial culture and incubating it at 37°C for 18–24 hours, a color change from red to yellow indicates acid production due to sugar fermentation. If gas is produced (such as CO₂ or H₂), bubbles will appear in the inverted tube. If no fermentation occurs, the medium remains red.
(2) Experimental Materials
1. Bacterial species: *Escherichia coli* and *Salmonella typhimurium* grown on agar slants for 18–24 hours. 2. Media: Glucose fermentation tubes, lactose fermentation tubes, and maltose fermentation tubes. 3. Reagents: Phenol red indicator and small inverted tubes.
(3) Experimental Methods
1. Inoculate *E. coli* and *S. typhimurium* into glucose and lactose fermentation tubes using a liquid inoculation technique. 2. Incubate the tubes at 37°C for 18–24 hours. 3. Observe the results: A yellow color change indicates acid production (+). The presence of gas bubbles in the inverted tube suggests both acid and gas production (⊕). No color change means the sugar was not fermented (-).
(4) Experimental Results
*Salmonella typhimurium*:
Glucose: + ⊕
Lactose: - ⊕
Second, Voges-Proskauer (VP) Test
(1) Experimental Principle
The VP test detects the ability of bacteria to produce acetylmethylcarbinol from glucose. This compound reacts with α-naphthol and potassium hydroxide under alkaline conditions to form a red compound, indicating a positive result. Common organisms like *Enterobacter aerogenes* typically show a positive reaction, while *E. coli* usually does not.
(2) Experimental Materials
1. Bacterial species: *E. coli* and *Enterobacter aerogenes* from 18–24 hour agar slants. 2. Medium: Glucose peptone broth. 3. Reagents: VP reagent (40% KOH with 0.3% creatine and 6% α-naphthol in alcohol).
(3) Experimental Methods
1. Inoculate each organism into separate glucose peptone broth tubes. 2. Incubate at 37°C for 48 hours. 3. Add 1 ml of KOH solution and 1 ml of α-naphthol solution to each tube, shake well, and let stand for 5–15 minutes. 4. Observe for a red color change, which indicates a positive result.
(4) Experimental Results
A red color change indicates a positive result; no color change means a negative result.
Third, Methyl Red Test
(1) Experimental Principle
The methyl red test determines whether bacteria produce stable acids during glucose fermentation. If the pH drops below 4.5, the methyl red indicator turns red (positive). If the acid is further metabolized into non-acidic products, the pH remains above 6.2, and the indicator stays yellow (negative). *E. coli* typically gives a positive result, while *Enterobacter aerogenes* is often negative.
(2) Experimental Materials
1. Bacterial species: *E. coli* and *Enterobacter aerogenes* from 18–24 hour agar slants. 2. Medium: Glucose peptone broth. 3. Reagent: Methyl red reagent.
(3) Experimental Methods
1. Inoculate each organism into separate glucose peptone broth tubes. 2. Incubate at 37°C for 2–3 days. 3. Add 2–3 drops of methyl red reagent, mix, and observe the color change.
(4) Experimental Results
*E. coli*: + *Enterobacter aerogenes*: -
Fourth, Citrate Utilization Test
(1) Experimental Principle
The citrate utilization test assesses whether bacteria can use sodium citrate as their sole carbon source. The medium contains ammonium dihydrogen phosphate as the only nitrogen source. If the bacteria can utilize citrate, they grow and produce alkaline byproducts, causing the medium to turn from green to dark blue (positive). *E. coli* cannot use citrate, so it does not grow, and the medium remains green (negative).
(2) Experimental Materials
1. Bacterial species: *E. coli* and *Enterobacter aerogenes* from 18–24 hour agar slants. 2. Medium: Citrate slant.
(3) Experimental Methods
1. Inoculate each organism onto a citrate slant. 2. Incubate at 37°C for 24 hours. 3. Observe for growth and color change in the medium.
(4) Experimental Results
*Enterobacter aerogenes*: + (lawn growth, medium discoloration) *E. coli*: - (no growth, medium remains green)
Water flosser dental hygiene,Dental Oral Irrigator,Water flosser teeth whitening,Water toothpick,Water pik
Shenzhen Shengkang Electronic Technology Co.,Ltd , https://www.shk-beauty.com