Control of Microbial Growth: Disinfectants, Antiseptics, and Antibiotics

Question 1

What are the three types of control measures that can be used to kill or inhibit the growth of microorganisms?

Answer 1

• Physical methods
  
  • decontamination or disinfection of surfaces, and sterilization of instruments, reagents, and media
• Biological methods (biological control)
• Chemical methods
  
  • germicides, disinfectants, antiseptics, antibiotics

Question 2

What are the most common mechanisms that inhibit cell growth?

Answer 2

• The most common actions are:
  
  • disruption of cell membranes
  • lysis of cell walls
  • or interference with the nucleic acid or protein synthesis.

Question 3

What are disinfectants?

Answer 3

• Disinfectants are bactericidal or bacteriostatic chemicals which are generally not safe to use on animal tissue.

Question 4

What are antiseptics?

Answer 4

Antiseptics:

• Antiseptics are chemicals which kill or inhibit the growth of microorganisms and are safe to use on animal tissue.
• Antiseptics may be used to treat wounds or may be used as mouthwashes.

Question 5

What are antibiotics?

Answer 5

• Antibiotics are chemicals produced by one microorganism which kill or inhibit the growth of another microorganism.
• Naturally produced antibiotics are exploited by humans and used both internally and externally in the treatment of infectious disease.

Question 6

What is the Kirby-Bauer method?

Answer 6

• a bioassay that determines the effectiveness of a variety of antibiotics, antiseptics, and disinfectants on the growth of bacterial species.
• An agar plate of the suitable culture medium is inoculated by the overlay method: a known number of bacterial cells are gently but evenly suspended in warm (~50 C) soft agar and the suspension is poured quickly across a solid agar surface.
• Filter paper discs containing known concentrations of different antimicrobial agents are then laid atop the bacterial suspension.
• Upon incubation, the bacterial suspension will grow into an even lawn.
• If the substance contained in a filter disk is inhibitory, a clear zone of inhibition will surround the paper disc within the lawn of bacterial growth. T
• he zone of inhibition around the filter paper disc is measured in millimeters, and the size of the zone is an expression of the agent’s effectiveness and can be compared quantitatively against other substances.