Controlling Microbial Growth Flashcards
What is sterilization?
- destruction or removal of all viable microorganisms (including endospores and viruses)
- uses a sterilant
What is decontamination?
- cleaning and removing organic matter and debris
- ex: wiping down a table
What is disinfection?
- killing, inhibition, or removal of pathogenic microorganisms
- uses a disinfectant
- used on inanimate objects
- ex: wiping down a table with spray
What is sanitization?
- reduction of microbial population to levels deemed safe (based on public health standards)
- uses a sanitizer
What is antisepsis?
- 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
What is chemotherapy?
use of chemicals to kill or inhibit growth of microorganisms within host tissue
How is moist heat used to control microbes?
- destroys bacteria, fungi, and viruses
- 3 types: boiling, pasteurization, autoclaving
Does boiling sterilize?
will not always destroy endospores, so does not necessarily sterilize
What is pasteurization?
- 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
What is autoclaving?
- 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
What is dry heat sterilization?
- 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)
How are low temperatures used to control microbes?
- 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
How is ultraviolet (UV) radiation used to control microbes?
- 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.
How is ionizing radiation used to control microbes?
- beta, gamma, and X rays are ionizing radiation
- penetrate deep into objects
How is filtration used to control microbes?
- reduces microbial populations
- sterilization of heat-sensitive solutions (must use a membrane filter with defined pore size)
- also used for air
What is an antimicrobial agent?
- a natural or synthetic chemical that kills or inhibits the growth of microbes
- can be cidal or static
What does cidal mean?
- 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
What does static mean?
- 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
What does lytic mean?
- suffix indicating a chemical agent that kills and lyses
- decreases total cell count and viable cell count
- ex: bacteriolytic
What is the minimum inhibitory concentration (MIC)?
lowest concentration of drug that inhibits growth of a pathogen
What is the minimum lethal concentration (MLC)?
- lowest concentration of drug that kills a pathogen
- higher than MIC (usually 2-4x MIC)
What are the different methods to determine the level of antimicrobial activity?
- Dilution Susceptibility Test
- Disk Diffusion Test
- Kirby-Bauer Method
What is the Dilution Susceptibility Test?
- 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)
What is the Disk Diffusion Test?
- 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
What is the Kirby Bauer Method?
- 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
What are factors influencing the effectiveness of an antimicrobial agent?
- population size
- population composition
- concentration or intensity of the agent
- duration of exposure
- temperature
- local environment
- route
