Experiments to determine the effect of chemical factors on microorganisms
Experiments to determine the effect of chemical factors on microorganisms
Commonly used chemical disinfectants mainly include heavy metals and their salts, phenols, alcohols, aldehydes and other organic compounds, as well as iodine, surfactants and so on. Their bactericidal or bacteriostatic effects are mainly caused by denaturing the bacterial proteins or combining with the -SH group of the enzyme to make the enzyme inactive.
Operation method
Determination of carbolic acid coefficient
Principle
In order to compare the bactericidal ability of various chemical disinfectants, often carbonic acid as a standard, that is, a disinfectant for different dilutions, under certain conditions, a certain period of time to kill all the test microorganisms of the highest dilution concentration, and to achieve the same effect of the highest dilution of the carbonic acid ratio, known as this disinfectant on the microorganisms of the carbonic acid coefficient (phenol coefficient). The greater the carbonic acid coefficient, the greater the sterilizing power of the disinfectant.
Materials and Instruments
Escherichia coli Staphylococcus albus Move 1. Sterilization of chemicals For more product details, please visit Aladdin Scientific website.
Beef paste peptone agar medium Iodine Mercury Carbonic acid Alcohol Lysol Neosporin Gentian violet GV violet
Petri dish, filter paper, test tubes, straws
(1) Aspirate 0.2 ml of Staphylococcus albicans culture for 18 hours with a sterile pipette in a sterile dish.
(2) Pour in beef paste peptone agar culture based on the above petri dish which has been dissolved and cooled to about 45°C, shake well, place horizontally, and leave to congeal.
(3) The above solidified petri dish is marked with a marker on the bottom of the dish into eight equal portions, and the name of one drug is labeled within each portion.
(4) After immersing small round pieces of filter paper in each of the various drugs with sterile forceps, removing them, and removing the excess liquid from the inner wall of the test tube, the pieces of paper are placed aseptically in pairs into the small area of the petri dish.
(5) Place the above bacteria-containing petri dishes with filter paper sheets inverted in a 37℃ greenhouse and incubate them for 24 hours, then take them out to determine the size of the ring of inhibition and state their bactericidal strength.
2. Determination of the carbonic acid coefficient
(1) Prepare 5% (1:20) carbolic acid solution to different concentrations according to Table IX-1, 5 ml per tube.
(2) The drug to be tested (Lysol) is first prepared as a 1:20 stock solution, and then prepared in different concentrations according to Table IX-2, 5 ml per tube. 
(3) Thirty tubes of meat paste peptone liquid medium were taken, tubes 1 to 15 were labeled with five concentrations of carbolic acid, three tubes of each concentration, and each of the three tubes was treated in 5, 10, and 15 minutes, and tubes 16 to 30 were labeled with five concentrations of Lysol, again three tubes of each concentration, and each of the three tubes was treated in 5, 10, and 15 minutes.
(4) In each of the above different concentrations of carbolic acid and Lysol solutions, access 0.5 ml of E. coli solution and shake well. Note that each tube was inoculated at 5, 10 and 15 minutes from the time of inoculation, using the same inoculation loop to take a loop from each tube into the above labeled liquid medium test tubes. 
(5) Incubate in the greenhouse at 37℃ for 48 hours, observe and record the growth. Growth of the solution turbid, indicated by "+"; non-growth of the solution clarified, indicated by "-".
(6) Calculate the coefficient value to find the maximum dilution of carbolic acid and lysol that grows at 5 minutes and does not grow at 10 and 15 minutes, and calculate the ratio of the two. For example, if the maximum dilution of carbolic acid that kills E. coli in 10 minutes is 1:70, and Lysol is 1:250, then the coefficient of carbolic acid of Lysol is 250/70 = 3.6.3. Results(1) Lethality of various chemicals against C. albicans 
(2) Determination and calculation of carbolic acid coefficient 