Week 7

Question 1

What chemical/physical agents are used to control growth of MO’s?

Answer 1

Heat
Radiation
Toxic chemicals

Question 2

Microbial growth helps

Answer 2

curb the transmission of infectious microbes

Question 3

Examples of microbial growth control practical applications

Answer 3

• routinely wash fresh fruits and vegetables to remove attached microorganisms
• inhibit microbial growth on body surfaces by washing.

Question 4

Sterilization

Answer 4

killing or removal of all microorganisms (including viruses)
* In many circumstances, sterility is not required.

Question 5

Decontamination

Answer 5

the treatment of an object or surface to make it safe
to handle

Question 6

Disinfection

Answer 6

a process that directly targets pathogens although it
may not eliminate all microorganisms.

Question 7

Disinfection Requires

Answer 7

agents called disinfectants
that actually kill microorganisms or severely
inhibit their growth.

Question 8

Where is microbial growth control used extensively?

Answer 8

Industry
Medicine
Home

Question 9

What are 3 classes of physical controls?

Answer 9

1. Heat: is the most widely
2. Radiation
3. Filtration

Question 10

How is effectiveness of heat as a sterilant quantified?

Answer 10

By decimal reduction time (D)

Question 11

What is Decimal reduction time?

Answer 11

The time required at a given temperature for a 10-fold reduction in
the viability of a microbial population.

Question 12

What is the relationship between D and temp?

Answer 12

exponential

Question 13

What are the types of heat?

Answer 13

• Moist heat has better penetrating power
• Dry heat.

Question 14

Temperature

Answer 14

heat killing proceeds more rapidly as the
temperature rises.

Question 15

What is thermal decimal time?

Answer 15

• Another way to characterize the heat sensitivity of an organism
• The time it takes to kill all cells at a given temperature.

Question 16

How to determine thermal decimal time?

Answer 16

Samples of a cell suspension are heated for different times, mixed with
culture medium, and incubated.
* Is independent of the original cell number
* A longer time is required to kill all cells in a large population than in a
small one.

Question 17

What factors influence the effectiveness of heat?

Answer 17

1. The presence of endospore-forming bacteria in a heat-treated sample can influence both the decimal reduction and thermal death times.
2. The medium in which heating takes place
   * This is especially relevant in food canning procedures.

Question 18

an endospore is?

Answer 18

• very dehydrated
• contains calcium dipicolinate
• contains small acid-soluble spore proteins (SASPs) that help confer heat stability on the structure.

Question 19

pH

Answer 19

Microbial death is more rapid at acidic pH, and acidic foods such as tomatoes, fruits, and pickles are easier to sterilize than neutral-pH foods such as corn and beans.

Question 20

High concentrations of sugar, proteins, and fats do what?

Answer 20

decrease heat penetration and usually increase the resistance of organisms to heat

Question 21

High salt concentrations do what?

Answer 21

may either increase or decrease heat resistance, depending on the organism.

Question 22

What is an autoclave?

Answer 22

a sealed heating device that uses steam under pressure
to kill microorganisms

Question 23

What temp kills endospores?

Answer 23

endospores requires heating at temperatures
above the boiling point of water at 1 atm.

Question 24

who discovered pasteurization?

Answer 24

Louis pasteur

Question 25

How does pasteurization work?

Answer 25

At the temperatures and times standardized for the pasteurization of food products, all known pathogenic bacteria are killed.

Question 26

What is flash pasteurization?

Answer 26

To pasteurize milk, the liquid is passed through a tubular heat exchanger. Careful control of flow rate and the size and temperature of the heat source raises the temperature of the milk to 71°c for 15 sec (or even higher temperatures for shorter time periods after which it is rapidly cooled.

Question 27

what does pasteurization do?

Answer 27

uses heat to significantly reduce rather than totally eliminate the microorganisms found in liquids, such as milk.

Question 28

Physical microbial killing agents

Answer 28

* Heat * Radiation * ultraviolet (UV) light, X-rays, and gamma rays * Filtration

Question 29

What does radiation need to be between to kill exposed organisms?

Answer 29

220 and 300 nm

Question 30

What is UV radiation useful for?

Answer 30

disinfecting surfaces and air

Question 31

Where do we use UV radiation in day to day life?

Answer 31

▪ to decontaminate and disinfect the work surface of laboratory laminar flow hoods equipped with a “germicidal” UV light ▪ air circulating in the hospital ▪ food preparation rooms

Question 32

What is poor with UV radiation

Answer 32

poor penetrating power, limiting its use to the disinfection of exposed surfaces or air

Question 33

What is ionizing radiation

Answer 33

is electromagnetic radiation of sufficient energy to produce ions and other reactive molecular species from molecules with which the radiation particles collide.

Question 34

The unit of ionizing radiation

Answer 34

Roentgen

Question 35

The standard for sterilization

Answer 35

the absorbed radiation dose, measured in rads (100 erg/g) or grays (100 Gy=100 rad)

Question 36

X-rays or gamma rays

Answer 36

have sufficient energy and penetrating power to kill microorganisms in bulk items such as food products and medical supplies.

Question 37

Radiation is used to sterilize these pieces in lab/life

Answer 37

* surgical supplies * plastic labware * Drugs * even tissue grafts * certain foods and food products such * fresh poultry * meat products * spices

Question 38

When is filtration used?

Answer 38

Heat-sensitive liquids that are not sterilized by radiation are typically sterilized by filtration.

Question 39

what is the average filter pore size

Answer 39

0.2 μm average size is a minimum requirement

Question 40

What are the several types of filters are in routine use in microbiology

Answer 40

depth filters *membrane filters *nucleopore filters.

Question 41

What are depth filters?

Answer 41

a fibrous sheet made from an array of overlapping paper or glass fibers that traps particles in the network of fibers

Question 42

What are membrane filters

Answer 42

* The most common filters used for liquid sterilization in the microbiology laboratory * Composed of high-tensile-strength polymers manufactured in such a way as to contain a large number of tiny pores.

Question 43

What are nucleopore filters

Answer 43

A type of membrane filter * Made from a thin polycarbonate film that is treated with radiation and then etched with a chemical, yielding very uniform-sized holes.

Question 44

What are nucleopores commonly used for?

Answer 44

to isolate specimens for scanning electron microscopy.

Question 45

cidal agents

Answer 45

Agents that actually kill are called -cidal agents, with a prefix indicating the type of microorganism killed * Bactericidal agent * Fungicidal agent * viricidal agent

Question 46

static agents

Answer 46

Agents that inhibit growth are called -static agents, * bacteriostatic agent * Fungistatic compounds * viristatic compounds

Question 47

what is an AMA

Answer 47

natural or synthetic chemical that kills or inhibits the growth of microorganisms.

Question 48

Antibacterial agents are classified as

Answer 48

-static, -cidal, or -lytic

Question 49

bacteriostatic agents

Answer 49

typically inhibitors of some important biochemical process * bind relatively weakly * if the agent is removed, the cells can resume growing. * Some antibiotics, such as the sulfonamides, work in this way. * The clinical value of bacteriostatic antibiotics is their ability to keep a pathogenic bacterium from multiplying until the immune system can rid the body of the pathogen.

Question 50

Bactericidal agents

Answer 50

bind tightly to their cellular targets and by definition kill the cell. * the dead cells are not lysed, and total cell numbers, reflected in the turbidity of the culture, remain constant. * for example formaldehyde

Question 51

Bacteriolytic agents

Answer 51

kill cells by lysing them * affects both viable and total cell numbers * Example: * detergent that ruptures the cytoplasmic membrane * the antibiotic penicillin, which inhibits bacterial cell wall synthesis, resulting in cell lysis.

Question 52

What is the minimum inhibitory concentration (MIC)

Answer 52

determining the smallest amount of the agent needed to inhibit the growth of a test organism

Question 53

What is one way to determine MIC of a given agent

Answer 53

inoculate a series of tubes of liquid growth medium containing a test organism and dilutions of the agent.