Lecture 6- control of microbial growth

Question 1

what is sterilization?

Answer 1

the killing or removal of all viable organisms within a growth medium

Question 2

what is inhibition

Answer 2

effectively limiting microbial growth (no killing taking place)

Question 3

what is decontamination?

Answer 3

treatment of an object to make it safe to handle

Question 4

what is disinfection?

Answer 4

directly targets the removal of all pathogens but not necessarily all microorganisms

Question 5

what is the most widely used method of controlling microbial growth?

Answer 5

heat sterilization

Question 6

how does heat sterilization work?

Answer 6

the high temperature denatures macromolecules

Question 7

what can heat sterilization not sterilize against?

Answer 7

bacterial endospores because they’re heat resistant

Question 8

what is the decimal reduction time?

Answer 8

amount of time required to reduce viability tenfold
time it takes for a 10 fold reduction in bacterial numbers

Question 9

what is pasteurization?

Answer 9

the process of using precisely controlled heat to reduce the microbial load in heat sensitive liquids

Question 10

does pasteurization sterilize?

Answer 10

NO, it doesnt kill all organisms, thus is not sterilization

Question 11

what two processes kill coxiella burnetii heat resistant pathogen found in milk?

Answer 11

low temp, long time
-63C for 30 minutes
high temp, short time
-72C for 15 minutes

Question 12

what is the autoclave?

Answer 12

sealed device that uses steam under pressure

Question 13

what temperature does the water get to in the autoclave?

Answer 13

above 100C

Question 14

how does the autoclave ensure sterility?

Answer 14

121C for 15 minutes at 15 pounds per square inch

Question 15

what is radiation?

Answer 15

physical method of growth control

Question 16

what is radiation used for?

Answer 16

sterilization in the medical field and food industry (chicken, hamburger, spices…)

Question 17

what are examples of radiation that can reduce microbial growth?

Answer 17

microwaves
UV
X- rays
electrons

Question 18

how does UV reduce microbial growth?

Answer 18

has sufficient energy to cause modification and breaks in DNA

Question 19

what is the UV useful for?

Answer 19

decontaminating surfaces (cannot penetrate solid, opaque or light absorbing surfaces)

Question 20

what is ionizing radiation?

Answer 20

electromagnetic radiation that produces ions and other reactive molecules. generates electrons, hydroxyl radicals and hydride radicals

Question 21

what are sources of radiation?

Answer 21

cathode ray tubes
x rays
radioactive nuclides

Question 22

why might we use filtration to sterilize?

Answer 22

because it avoids the use of heat on sensitive liquids and gases

Question 23

how does filtration work?

Answer 23

pores of the filter are too small for organisms to pass through so it only allows liquid or gas to pass through

Question 24

using a membrane filter what are the 3 ways filtration can be accomplished?

Answer 24

syringe
pump
vacuum

Question 25

what are two different pore sizes the filter can have?

Answer 25

5 micrometer
0.2 micrometer

Question 26

what filter size is best?

Answer 26

0.2 because it prevents most bacteria from going through

Question 27

what are 3 ways antimicrobial agents can be classified?

Answer 27

bacteriostatic
bacteriocidal
bacteriolytic

Question 28

what is bacteriostatic?

Answer 28

prevents cell growth as long as teh antimicrobial agent is present

Question 29

what is bacteriocidal?

Answer 29

kills the cells (does not lyse them)

Question 30

what is bacteriolytic?

Answer 30

kills and lyses the cells

Question 31

what is minimum inhibitory concentration?

Answer 31

smallest amount of an agent needed to inhibit growth of a microorganism

Question 32

what does it mean that minimum inhibitory concentration varies with the organism used?

Answer 32

size
temp
pH

Question 33

what does the lowest concentration of MIC exhibit?

Answer 33

no growth but may still have living organisms

Question 34

if no colonies form on nutrient agar plates what does that mean?

Answer 34

minimal lethal concentration has occurred

Question 35

what is higher, minimum inhibitory concentration or minimal lethal concentrations?

Answer 35

minimal lethal concentrations

Question 36

what is a disc diffusion assay? what media is used? what does it form?

Answer 36

-uses solid media
-antimicrobial agent is added to filter paper disc
-minimum inhibitory concentration is reached at some distance
-forms a zone of inhibition
-area of no growth around disc

Question 37

the antimicrobial agents can be divided into two categories, what are they?

Answer 37

1. products used to control microorganisms in commercial and industrial applications
2. products designed to prevent growth of human pathogens in inanimate environments and on external body surfaces

Question 38

what is an example of a product used to control microorganisms?

Answer 38

chemicals in foods
air conditioning cooling towers
textile and paper products
fuel tanks

Question 39

what are the 4 products used to prevent growth?

Answer 39

sterilant
disinfectant
sanitizer
antiseptic

Question 40

what is a sterilant?

Answer 40

destroys all microorganisms including endospores!

Question 41

what is a disinfectant?

Answer 41

kills microorganisms but not all endospores
used on inanimate objects

Question 42

what is a sanitizer?

Answer 42

reduces the numbers of microorganisms on surfaces
ex. hand sanitizers

Question 43

what is an antiseptic?

Answer 43

kills or inhibits the growth of microorganisms
ex. mouth wash