This set of Basic Microbiology Questions and Answers focuses on “Evaluation of Antimicrobial Chemical Agents”.
1. Which of the following methods is used for determining the decrease in the amount of growth?
a) test done on agar medium plate
b) test done into an agar medium or broth
c) test done by transfering water-soluble substances to sterile media
d) by phenol-coefficient method
Explanation: The chemical agent is incorporated into an agar medium or broth, inoculated with the test organism, incubated, and then observed for (i) decrease in the amount of growth or (ii)complete absence of growth.
2. Liquid water-soluble substances appropriately diluted are dispensed into sterile test tubes, to which are added a measured amount of the test organism and then this is transferred into tubes of sterile media.This method helps in determining _____________________
a) whether the inhibitory action is bactericidal
b) whether the inhibitory action is bacteristatic
c) decrease in the amount of growth
d) complete absence of growth
Explanation: Liquid water-soluble substances appropriately diluted are dispensed into sterile test tubes, to which are added a measured amount of the test organism.At specified intervals, a transfer is made from this tube into tubes of sterile media that are then incubated and observed for the appearance of growth.It is necessary to ascertain whether the inhibitory action is bactericidal and not bacteriostatic.
3. We observe increased growth in nutrient agar plates as concentration of chemical agent is decreased.
Explanation: From laboratory evaluation of chemical antimicrobial agents it is found that there is an increased growth in nutrient agar plates as the concentration of chemical agents is reduced.
4. Which of the following acts as a test organism in the procedure of phenol-coefficient method?
a) Escherichia coli
b) Streptococcus faecalis
c) Staphylococcus aureus
Explanation: In the procedure of Phenol-Coefficient method the test organism employed is a specific strain of either Salmonella typhi or Staphylococcus aureus.This procedure is suitable for testing disinfectants miscible with water and exerting antimicrobial action in a manner similar to that of phenol.
5. Which of the following chemical agents lack penetrating power?
c) Ethylene oxide
Explanation: Beta-propiolactone is a chemical agent which is used for sterilizing instruments and heat-sensitive materials but it lacks the penetrating power.
6. Which of the following agent is used to disinfect skin?
d) Ethylene oxide
Explanation: Quaternaries like quaternary ammonium salts are used as a skin disinfectant due to its disinfectant property and detergent property.But it is not sporicidal in nature.
7. Iodine kills the microorganisms by causing denaturation of proteins.
Explanation: Alcohols, phenols and heavy-metal salts are used to kill the microorganisms by causing denaturation of proteins and reducing the enzyme activity.
8. Which of the following is the mode of action of formaldehyde?
a) interference with glycolysis
b) shows oxidizing property
c) combines with vital nitrogen compounds
d) changes the permeability of cytoplasmic membrane
Explanation: Formaldehyde is an extremely reactive chemical.It combines readily with vital organic nitrogen compounds such as proteins and nucleic acids.This interaction accounts for its antimicrobial activity.
9. For sterilization of plastic syringes in hospitals which of the following agents are used?
a) ethylene oxide
d) heavy metals
Explanation: Ethylene oxide has an excellent power to penetrate and so it will pass through and sterilize large packages of materials and even plastics such as plastic syringes in hospitals which are sterilized by its vapours.
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