1. Monosaccharide fermentation test
(1) Experimental principle
In monosaccharide fermentation, glucose, lactose or maltose are separately added to the peptone water medium to a final concentration of 0.75 to 1%. And add a certain amount of phenol red indicator and small inverted tube to make a monosaccharide fermentation tube. The inoculated bacteria are cultured at 37 ° C for 18 to 24 hours. If the sugar can be decomposed, the phenol red indicator turns from red to yellow. Formic acid is formed by a gas such as CO2 and H2, and bubbles are accumulated in the small inverted tube; if it is not decomposed, the indicator does not change color.
(2) Experimental materials
1. Species: Escherichia coli, Salmonella typhimurium 18~24 hours agar slant culture.
2. Medium: glucose fermentation tube, lactose fermentation tube, etc.
(3) Experimental methods
1. Inoculate Salmonella typhimurium and Escherichia coli in a glucose and lactose fermentation tube according to a liquid inoculation method.
2. Incubate at 37 ° C for 18 to 24 hours.
3. Observation results: Since some bacteria can decompose a certain sugar to produce acid, the pH in the medium drops below 7.0. Under the phenol red indicator, the color of the medium changes from red to yellow. The acid generator is represented by "+". If gas is generated at the same time, bubbles appear in the small inverted tube in the medium. This is acid production and gas production. It is expressed as "⊕". If it does not decompose, the indicator does not change color. Said.
(4) Experimental results
Salmonella typhimurium
Glucose + ⊕
Lactose - ⊕
Second, VP (Voges-Proskauer) test
(1) Experimental principle
Some bacteria, such as aerogens, decompose glucose to produce pyruvic acid, decarboxylation of pyruvic acid, produce acetylmethylmethanol, oxidize to diacetyl in an alkaline environment, and then combine with sulfhydryl groups in the medium to form a red compound, V-P The test was positive.
(2) Experimental materials
1. Species: Escherichia coli, Aerogenophilus 18~24 hours agar slant culture.
2. Medium: Glucose protein hydrophobic medium.
3. Reagents: VP reagent [40% potassium hydroxide aqueous solution (containing 0.3% creatine) and 6% α-naphthol alcohol solution].
(3) Experimental methods
1. Inoculate E. coli separately, and the aerogenic bacillus is in two dextrose proteins.
2. After incubating at 37 ° C for 48 hours, remove 1 ml of KOH 1 ml and α-naphthol solution, shake well, and let stand on the tube rack for 5-15 minutes.
(4) Experimental results
The culture medium turned red to be positive and did not change to negative.
Third, methyl red test
(1) Experimental principle
Some bacteria such as E. coli decompose glucose to produce pyruvic acid, which is then decomposed into formic acid, acetic acid, lactic acid, etc., so that the pH of the medium is reduced to 4.5 or less, and the methyl red indicator is red, which is a positive reaction; If the amount of acid or the generated acid is further converted into alcohol, aldehyde, gas, water, etc., the pH of the medium is still above pH 6.2, and the methyl red indicator is yellow, which is a negative reaction.
(2) Experimental materials
1. Species: Escherichia coli, Acetobacter 18~24 hours agar slant culture.
2. Medium: Glucose protein hydrophobic medium.
3. Reagent: methyl red reagent.
(3) Experimental methods
1. Inoculate Escherichia coli and Aerogenes in two glucosinolate media.
2. Incubate at 37 °C for 2~3 days, add 2~3 drops of methyl red reagent, mix well, observe the result.
(4) Experimental results
E. coli: +, aerogenic bacillus: -.
Fourth, citrate utilization test
(1) Experimental principle
The citrate medium is a comprehensive medium in which sodium citrate is the sole carbon source and ammonium dihydrogen phosphate is the sole nitrogen source. Generally, bacteria can use ammonium dihydrogen phosphate as a nitrogen source, but it is not necessarily able to decompose citrate to obtain a carbon source. Therefore, according to whether the use of citrate can be used to identify bacteria, such as gas-producing bacilli can use strontium salt as a carbon source, bacteria grow and multiply, form lawn, decompose citrate to form alkaline carbonate, make the medium PH Increased to above 7.0, from green to dark blue, positive for citrate test; while E. coli can not decompose citrate, can not get carbon source, can not grow, sterile moss formation, medium color No change, negative for the citrate utilization test.
(2) Experimental materials
1. Species: Escherichia coli, Acetobacter 18~24 hours agar slant culture.
2. Medium: citrate bevel.
(3) Experimental methods
1. Inoculate Escherichia coli and Aerogenes in two citrate slant medium.
2. Observe the results after incubating at 37 ° C for 24 hours.
(4) Experimental results
Aerobacteria: + (with lawn growth, medium discoloration)
E. coli: - (aseptic moss growth, medium does not change color)
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