1. Monosaccharide fermentation test
(1) Experimental principle
Monosaccharide fermentation is to add glucose, lactose or maltose, etc. into the peptone water medium, so that the final concentration is 0.75 ~ 1%. Add a certain amount of phenol red indicator and a small inverted tube to make a monosaccharide fermentation tube. Inoculate the bacteria and incubate at 37 ℃ for 18-24 hours. If the sugar can decompose and produce acid, the phenol red indicator will change from red to yellow. Formic acid is formed by gases such as CO2 and H2, and bubbles accumulate in the small inverted tube; without decomposition, the indicator does not change color.
(2) Experimental materials
1. Strain: Escherichia coli, typhoid bacillus 18-24 hours agar slant culture.
2. Culture medium: glucose fermentation tube, lactose fermentation tube, etc.
(3) Experimental method
1. Inoculate typhoid bacillus and Escherichia coli into glucose and lactose fermentation tubes separately according to liquid inoculation method.
2. Incubate in a 37 ° C incubator for 18 to 24 hours.
3. Observation result: because some bacteria can decompose a certain carbohydrate to produce acid, the pH in the medium drops below 7.0, and under the display of phenol red indicator, the color of the medium changes from red to yellow. Acid generators are indicated by "+". If gas is generated at the same time, bubbles appear in the small inverted tube in the medium. This is acid generation and gas generation. It is indicated by "?". If it does not decompose, the indicator will not change color. Use "- "Means.
(4) Experimental results
Typhoid coli
Glucose +?
Lactose-?
2. VP (Voges-Proskauer) test
(1) Experimental principle
Some bacteria, such as aerogenes, decompose glucose to produce pyruvate, pyruvate is decarboxylated to produce acetylmethyl methanol, and is oxidized to diacetyl in an alkaline environment, and then combined with the guanidine group in the medium to produce a red compound, V-P The test is positive.
(2) Experimental materials
1. Strains: Escherichia coli, aerobic bacteria 18-24 hours agar slant culture.
2. Culture medium: glucose peptone water culture medium.
3. Reagents: VP reagent [40% potassium hydroxide aqueous solution (containing 0.3% creatine) and 6% α-naphthol alcohol solution].
(3) Experimental method
1. Inoculate Escherichia coli and aerogenes in two glucose peptone waters respectively.
2. After incubating at 37 ° C for 48 hours, take out 1ml of KOH and 1ml of α-naphthol solution, shake well, and let stand on the test tube rack for 5-15 minutes.
(4) Experimental results
The culture medium turns positive for red, but not negative for color.
Three, methyl red test
(1) Experimental principle
Some bacteria, such as E. coli, decompose glucose to produce pyruvate, which is then decomposed into formic acid, acetic acid, lactic acid, etc., which lowers the pH value of the culture medium to below 4.5, and the methyl red indicator is red. If the amount of acid produced is low or the acid is further converted into alcohol, aldehyde, gas, water, etc., the pH of the culture medium is still above pH 6.2, and the addition of methyl red indicator shows yellow, which is a negative reaction.
(2) Experimental materials
1. Strains: Escherichia coli, aerobic bacteria 18-24 hours agar slant culture.
2. Culture medium: glucose peptone water culture medium.
3. Reagents: methyl red reagent.
(3) Experimental method
1. Inoculate Escherichia coli and Aerobacterium respectively into two glucose peptone water culture media.
2. Incubate at 37 ° C for 2 ~ 3 days, take out, add 2 ~ 3 drops of methyl red reagent, mix well, and observe the results.
(4) Experimental results
E. coli: +, aerogenes:-.
4. Utilization test of citrate
(1) Experimental principle
Citrate medium is a comprehensive medium, in which sodium citrate is the sole carbon source and ammonium dihydrogen phosphate is the sole nitrogen source. In general, bacteria can use ammonium dihydrogen phosphate as a nitrogen source, but may not necessarily decompose citrate to obtain a carbon source. Therefore, according to whether citrate can be used to identify bacteria, for example, aerogenes can use citrate as a carbon source, bacteria grow and multiply, form moss, decompose citrate to generate alkaline carbonate, and make the medium PH It rises above 7.0 and changes from green to dark blue, positive for citrate utilization test; but E. coli cannot decompose citrate, can not get carbon source, can not grow, sterile moss is formed, medium color No change, negative for citrate utilization test.
(2) Experimental materials
1. Strains: Escherichia coli, aerobic bacteria 18-24 hours agar slant culture.
2. Culture medium: slant of citrate.
(3) Experimental method
1. Inoculate Escherichia coli and Aerobacterium respectively into two branches of citrate slant medium.
2. Observe the result after incubating at 37 ℃ for 24 hours.
(4) Experimental results
Aeromonas: + (with moss growth, medium discoloration)
Escherichia coli:-(sterile moss growth, the medium does not change color)
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