Chapter 2 - 1.A - Media and Culture/Tools of the Laboratory

Question 1

Metabolism

Answer 1

the chemical reactions in the body’s cells that change food into energy

Question 2

Isolates

Answer 2

a culture of microorganisms isolated for study.

Question 3

Innoculating Loop

Answer 3

also called a smear loop, inoculation wand or microstreaker, is a simple tool used mainly by microbiologists to pick up and transfer a small sample (inoculum) from a culture of microorganisms, e.g. for streaking on a culture plate.

Question 4

Accentuate

Answer 4

make more noticeable or prominent.
“his jacket unfortunately accentuated his paunch”

Similar:
focus attention on
bring/call/draw attention to
point up
underline
underscore
accent
highlight
spotlight
foreground
feature
give prominence to
make more prominent
make more noticeable
play up
bring to the fore
heighten
stress
emphasize
put/lay emphasis on

Question 5

In order, what are the five basic techniques used to grow, manipulate, examine, and characterize microorganisms in the laboratory?

Answer 5

1. ) Inoculation - Seed sample/inoculum is introduced to medium.
2. ) Incubation - Medium is placed into an incubator in order for culture to grow. Incubator can have atmospheric controls such as gas (IE: Oxygen and Carbon Dioxide) and temperature.
3. ) Isolation - Culture may go through inoculation and incubation again in order to separate the needed microorganisms from others so that specific species can be obtained.
4. ) Inspection - Colonies on agar or broth cultures are observed macroscopically or microscopically, possibly with the aid of staining.
5. ) Identification - identity of the isolated microbe is determined, usually down to the species level. Inspection may be enough to determine species but additional techniques include biochemical tests, immunologic tests, and genetic analysis.

Question 6

Pure Culture

Answer 6

A growth medium that contains only a single known species or type of microorganism. This type of culture is most frequently used for laboratory study because it allows the systematic examination and control of one microorganism by itself.

Question 7

Mixed Culture

Answer 7

A container that holds two or more identified, easily differentiated species of microorganisms, not unlike a garden plot containing both carrots and onion.

Question 8

Contaminated Culture

Answer 8

Once pure or mixed (With known species) but has since had contaminants (Unwanted microbes of uncertain identity) introduced into it, like weeds into a garden. Contaminants get into cultures when the lids of tubes or petri dishes are left off for too long, allowing airborne microbes to settle into the medium. They can also enter on an incompletely sterilized inoculating loop or on an instrument that you have inadvertently reused or touched to the table or your skin.

Question 9

Media can be classified according to three properties.

Answer 9

Physical state, chemical composition, and functional type (purpose) media.

Question 10

What are examples of physical state media

Answer 10

Liquid, semisolid, solid that can be converted to liquid, and solid that cannot be liquefied.

Question 11

Agar

Answer 11

A polysaccharide found in seaweed and commonly used to prepare solid culture media.

The benefits of agar are numerous, it is solid at room temperature, and melts (liquefied) at boiling temperature of water. Once liquefied, agar does not resolidify until it cools to 42 degrees Celsius, so it can be inoculated and poured in liquid form at temperatures 45 to 50 C, that will not harm the microbes or the handler.

It is not itself a digestible nutrient for most microorganisms.

Question 12

What are chemically defined media?

Answer 12

Chemically defined (Synthetic) - Such media contain pure organic or inorganic compounds that vary little from one source to another and have a molecular content specified by means of an exact formula. Defined media may contain nothing more than a few essential compounds such as salts and amino acids dissolved in water or may be composed of a variety of defined organic and inorganic chemicals.

Most useful for research applications when the exact concentration of components in the media is controlled so that metabolic processes of the microbe can be precisely monitored.

Question 13

What are not chemically defined media?

Answer 13

Also known as complex media - If even one component of a given medium is not precisely defined, the medium belongs in the complex category. They contain extracts of animals, plants, or yeasts, including such materials as ground-up cells, tissues, and secretions. Examples are blood, serum, and meat extracts or infusions. Other possible ingredients are milk, yeast extract, soybean digests, and peptone.

Nutrient broth, blood agar, and MacConkey agar are all complex media.

Question 14

What are three main ways to accomplish isolation?

Answer 14

Streak plate technique, Pour plate technique and spread plate technique

Question 15

Streak Plate Technique

Answer 15

A small droplet of culture or sample is spread over the surface of the medium with an inoculating loop in a pattern that gradually thins out the sample and separates the cells spatially over several sections of the plate. The goal is to allow a single cell to grow into an isolated colony.

Question 16

Pour plate technique

Answer 16

Also called loop dilution, the sample is inoculated serially into a series of cooled but still liquid agar tubes so as to dilute the number of cells in each successive tube in the series. Inoculated tubes are then plated out (poured) into sterile Petri dishes and allowed to solidify. The end results, usually in the second or third plate, is that the number of cells per volume is so decreased that cells have ample space to grow into separate colonies. One difference between this and the streak plate method is that in this technique some of the colonies will develop deep in the medium itself.

Question 17

Spread Plate Technique

Answer 17

A small volume of liquid sample is pipetted onto the surface of the medium and spread around evenly by a sterile spreading tool (sometimes called a “hockey stick” because of its shape).

Question 18

What three qualities do microscopes provide?

Answer 18

Magnification, Resolution, and contrast.

Question 19

Positive Stain

Answer 19

Dye actually sticks to the specimen and gives it color

Question 20

Negative Stain

Answer 20

Dye does not stick to the specimen but settles some distance from its outer boundary, forming a silhouette. Cells do not stain because these dyes are negatively charged and are repelled by the negatively charged surface of the cells.

Question 21

Selective Media

Answer 21

Contains one or more agents that inhibit the growth of certain types of microbe or microbes but not others. This selects certain microbes and are very important in the initial stages of isolating a specific type of microorganism from samples containing dozens of different species-for example, feces, saliva, skin, water, and soil They speed up isolation by suppressing the unwanted background organisms and favoring growth of the desired ones.

Question 22

Differential Media

Answer 22

They do not inhibit the growth of any particular microorganisms but are designed to display visible differences in how they grow. Differentiation shows up as variations in colony size, color, in media color changes, or in the formation of gas bubbles and precipitates.

Question 23

Metabolic pathway

Answer 23

a sequence of chemical reactions undergone by a compound or class of compounds in a living organism.