Bacterial bio-chemical test - stone milk test

, test principle
is both a pH indicator and a redox indicator, in the acid solution (pH 4.5) is red, in alkaline (pH 8.3) is blue,
culture
the basic color should be purple blue (pH 6.8). Stone can also be reduced to a colorless mother by certain bacteria.
milk contains lactose and three
proteins
namely casein, milk protein and lactocyclin.
milk coagulation is mainly caused by bacteria containing lactase, which converts casein into a side casein, or is caused by the precipitation of casein by producing large amounts of acid from lactose fermentation.
bacteria produce lipases that break down fat in milk to form a yellow clear liquid.
some bacteria have casein hydrolysis enzymes that catalyz casein hydrolysis and eventually convert them into casein deposits in transparent liquids, a process known as proteinprotein.
II,
media
skimmed milk powder 100.0 g
isch appropriate amount
water 1000.0 mL
the milk powder fully dissolved in water, adjusted to pH 6.8, added stone solution until the purple blue (pH 6.8), installed
test tube
, each tube about 5 mL. Sterilise at 115 degrees C at 10 min, cool quickly and store in the fridge.
the preparation method of the stone crucible solution: called taking the stone crucible 2.5 g, put it in the crucible and crush it, and place it in a
-burning bottle containing 40% ethanol aqueous solution 50 mL
Medium, bring to the boil 1 min, set aside about 10 min, remove the above liquid into another besotted bottle, add 40% ethanol aqueous solution 50 mL to the original burnt, and boil for another 1 min.
add the upper liquid to the previous liquid, mix the two upper liquid evenly, centrifugal precipitation, pour the upper liquid into the 100 mL
sa volume
, with 40% ethanol to 100 mL, drip 1 M hydrochloric acid until the solution is purple, that is, 2.5% stone solution.
95% ethanol 42.1 mL plus water to 100 mL is 40% ethanol solution.
Three, test method
to be tested bacteria 18 to 24 h culture inoculation, if anaerobic spores, should be added to the medium tube aseptic iron chips or nails, and other coverage, 36±1 degrees C culture 1-14 days.
, the test results judge
1. Pink: Lactose is fermented to produce acid;
2. Purple blue: Lactose is fermented to maintain the primary color;
3. Blue: alkaline reaction, lactose for fermentation, bacteria break down the medium containing nitrogen substances, producing alkaline substances;
4. White: stone is reduced;
5. Clarification: milk protein digestion ();
. Coagulation will become clotting: due to large amounts of acid production, milk eggs are solidified;
7. Production: lactose is broken down to produce acid gas, strong fermentation can destroy clots.
5, description
If there is no skimmed milk powder, fresh milk can be placed in the refrigerator overnight, in addition to the cream layer above, the skimmed milk in the flowing steam
heating
sterilized 1 h, cooled to less than 10 degrees C, to sterilise the gauze
filtering
, add stone solution to the lilac so far, sub-pack test tube, sterilization before.
Zhang Hui
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