Controlling Microbial Growth

Question 1

What is sterilization?

Answer 1

• destruction or removal of all viable microorganisms (including endospores and viruses)
• uses a sterilant

Question 2

What is decontamination?

Answer 2

• cleaning and removing organic matter and debris

- ex: wiping down a table

Question 3

What is disinfection?

Answer 3

• killing, inhibition, or removal of pathogenic microorganisms
• uses a disinfectant
• used on inanimate objects
• ex: wiping down a table with spray

Question 4

What is sanitization?

Answer 4

• reduction of microbial population to levels deemed safe (based on public health standards)
• uses a sanitizer

Question 5

What is antisepsis?

Answer 5

• prevention of infection of living tissue
• uses an antiseptic (germicide) which is a chemical agent that kills or inhibits growth of microorganisms when applied to tissue

Question 6

What is chemotherapy?

Answer 6

use of chemicals to kill or inhibit growth of microorganisms within host tissue

Question 7

How is moist heat used to control microbes?

Answer 7

• destroys bacteria, fungi, and viruses

- 3 types: boiling, pasteurization, autoclaving

Question 8

Does boiling sterilize?

Answer 8

will not always destroy endospores, so does not necessarily sterilize

Question 9

What is pasteurization?

Answer 9

• controlled heating at temperatures well below boiling
• used for wine, milk, and other beverages
• kills pathogens present and slows spoilage
• reduces the total microbial load
• does not necessarily sterilize

Question 10

What is autoclaving?

Answer 10

• effective against all types of microbes
• sterilizes
• works at a pressure of 15 psi and a temperature of 121 C (steam)
• takes 15-20 minutes

Question 11

What is dry heat sterilization?

Answer 11

• less effective than moist heat sterilization
• requires higher temperatures and longer exposure times (160-170 C for 2-3 hours)
• flaming/incineration is an example (flaming inoculation loops)

Question 12

How are low temperatures used to control microbes?

Answer 12

• freezing stops microbial reproduction due to lack of liquid water
• some microorganisms are killed by ice crystal disruption of cell membranes
• refrigeration slows microbial growth and reproduction

Question 13

How is ultraviolet (UV) radiation used to control microbes?

Answer 13

• UV is non-ionizing radiation
• most bactericidal wavelength is 260 nm
• causes thymine dimers in DNA
• has a poor penetrating power so it is limited to the disinfection of surfaces, air, and water
• will not penetrate glass, plastic, dirt films, etc.

Question 14

How is ionizing radiation used to control microbes?

Answer 14

• beta, gamma, and X rays are ionizing radiation

- penetrate deep into objects

Question 15

How is filtration used to control microbes?

Answer 15

• reduces microbial populations
• sterilization of heat-sensitive solutions (must use a membrane filter with defined pore size)
• also used for air

Question 16

What is an antimicrobial agent?

Answer 16

• a natural or synthetic chemical that kills or inhibits the growth of microbes
• can be cidal or static

Question 17

What does cidal mean?

Answer 17

• suffix indicating a chemical agent that kills, but does not lyse
• kills pathogens and many non-pathogens, but not necessarily endospores
• levels off total cell count and decreases viable cell count
• ex: bactericidal, fungicidal, viricidal

Question 18

What does static mean?

Answer 18

• suffix indicating a chemical agent that inhibits growth
• levels of total cell count and viable cell count
• growth resumes when agent is removed
• ex: bacteriostatic, fungistatic

Question 19

What does lytic mean?

Answer 19

• suffix indicating a chemical agent that kills and lyses
• decreases total cell count and viable cell count
• ex: bacteriolytic

Question 20

What is the minimum inhibitory concentration (MIC)?

Answer 20

lowest concentration of drug that inhibits growth of a pathogen

Question 21

What is the minimum lethal concentration (MLC)?

Answer 21

• lowest concentration of drug that kills a pathogen

- higher than MIC (usually 2-4x MIC)

Question 22

What are the different methods to determine the level of antimicrobial activity?

Answer 22

• Dilution Susceptibility Test
• Disk Diffusion Test
• Kirby-Bauer Method

Question 23

What is the Dilution Susceptibility Test?

Answer 23

• a series of broths with increasing concentration of agent
• the smallest amount of agent needed to inhibit the growth of a test organism is the MIC
• broth from which the microbe can’t be recovered is the MLC (need to plate to see if the microbe is still viable)

Question 24

What is the Disk Diffusion Test?

Answer 24

• a nutrient agar plate is inoculated with liquid culture of a test organism
• discs containing antimicrobial agents are placed on the surface
• the plate is incubated for 24-48 hours
• zones of inhibition are measured

Question 25

What is the Kirby Bauer Method?

Answer 25

• used to determine the effectiveness of certain antimicrobials
• tables relate zone diameter to degree of microbial resistance
• can be resistant (R), intermediate (I), or susceptible (S)
• largest zone diameter= susceptible

Question 26

What are factors influencing the effectiveness of an antimicrobial agent?

Answer 26

• population size
• population composition
• concentration or intensity of the agent
• duration of exposure
• temperature
• local environment
• route