Micro Lab Exam 1

Question 1

Bacteria are ubiquitous

Answer 1

meaning they around everywhere

Question 2

Environmental factors that influence microbial growth

Answer 2

temperature, osmotic pressure, atmospheric gases, pH, and moisture.

Question 3

Microbes can exist in harsh environments, but most prefer moderate conditions.

Answer 3

temperatures between 20 to 40°C
moist conditions rather than very dry conditions
an oxygen-rich environment
an environment close to neutral pH

Question 4

Agar plates are made by

Answer 4

pouring hot agar into a petri dish and allowing it to cool. Often, condensation will form on the lid. Condensation often forms which could fall down onto the agar surface causing contamination or dispersion of any bacterial colonies. To prevent this, plates are always incubated upside down.

Question 5

Most bacteria are

Answer 5

mesophiles (grow between 20–40°C) and are incubated at 37°C (human body temperature).

Question 6

Agar plates are labeled on

Answer 6

bottom in case the lid becomes separated from the actual culture.

Question 7

What does an agar plate label include?

Answer 7

name of organism, agar type, researcher initials, sampling location, and date

Question 8

Why is it important to first moisten the applicator swab with sterile broth media?

Answer 8

it aids in picking up bacteria on objects and spreading them evenly on the agar plate

Question 9

Aseptic technique involves

Answer 9

working with microorganisms with the goal of preventing contamination of yourself and the microbial cultures you are using.

Question 10

Contaminating organisms may come from

Answer 10

the environment, your hands, or tools used during the process.

Question 11

Pure cultures are those that only contain

Answer 11

one type of microorganism, and are necessary when trying to identify a particular microorganism.

Question 12

Microbial cultures are transferred from one medium to another by

Answer 12

inoculating loops or needles.

Question 13

Inoculating loops are used

Answer 13

to transfer an inoculum between tubes of broth or onto the surface of an agar slant or plate.

Question 14

A broth is

Answer 14

a liquid nutrient medium used to support the growth of microbes with the advantage of supporting rapid and large bacterial population growth.

Question 15

A broth is limited in that

Answer 15

one cannot see individual cells or colonies so pure cultures cannot be created in this medium.

Question 16

inoculating tools must be sterilized both before and after transfer by

Answer 16

heating to red hot in the flame of a Bunsen burner or in a micro incinerator.

Question 17

The mouth of a glass culture tube should be

Answer 17

through the flame of a Bunsen burner in order to reduce contamination when the cap is first removed and again before it is replaced.

Question 18

The cap of a tube should never

Answer 18

be placed on the bench; instead, it should be held by the little finger of one hand.

Question 19

agar media

Answer 19

bacterial culture medium that contains agar as a solidifying agent and is used for growing microorganisms

Question 20

agar plate

Answer 20

bacterial culture medium containing agar poured into a petri dish

Question 21

agar slant

Answer 21

bacterial culture medium containing agar in a test tube that is allowed to solidify at an angle and forms a solid, slanted surface

Question 22

aseptic technique

Answer 22

a set of procedures employed in the handling of microbes without causing contamination from outside sources

Question 23

colony

Answer 23

a visible mass of microorganisms formed by replication of a single microorganisms on an agar surface, often in a petri dish

Question 24

inoculating loop

Answer 24

a sterilizable tool made of wire, used to implant or move microorganisms

Question 25

inoculum

Answer 25

a small amount of microorganism used to start a new culture

Question 26

liquid broth culture

Answer 26

a liquid nutrient used for the propagation of microorganisms

Question 27

petri dish

Answer 27

a shallow, transparent glass or plastic dish that is covered by a larger lid

Question 28

pure culture

Answer 28

a bacterial culture containing only one strain of microorganism

Question 29

sterile

Answer 29

an environment devoid of any living cells

Question 30

Pure cultures are necessary when

Answer 30

trying to identify a particular organism.

Question 31

Which of the following patterns is used to streak an agar slant?

Answer 31

pass the loop across the surface of the slant

Question 32

Quadrant streak plate isolation techniques

Answer 32

isolate one bacterial strain from a mixture of bacteria and are helpful in determining whether a bacterial culture may be pure.

Question 33

two noted drawbacks of quadrant streak plate

Answer 33

First, it can be difficult to master the technique, requiring practice to achieve consistent and acceptable results. Secondly, you cannot accurately count bacteria from a quadrant streak plate.

Question 34

The quadrant streak plate technique can be described as having four key steps:

Answer 34

Use aseptic technique to transfer a bacterial sample to an agar plate. Streak the bacterial sample across one quadrant (approximately ¼ of the agar surface) in a back-and-forth motion. Re-sterilize the loop and then drag the loop through the previously inoculated quadrant to pick up a small fraction of sample to the next quadrant surface. Repeat until four quadrants are completed in the same manner. Incubate the agar plate for 24 hours to grow isolated bacterial colonies.

Question 35

A successful streak plate provides

Answer 35

isolated colonies on the top of the agar by drag-diluting the colony forming units (CFUs) out across 4 sections of the plate.

Question 36

the last dilution quadrant shows

Answer 36

the isolated colonies.

Question 37

Colony Forming Unit CFUs

Answer 37

a unit used in microbiology to estimate the number of viable microorganism cells in a sample. Viable is defined as the ability to grow and multiply under the incubation conditions provided.

Question 38

culture

Answer 38

a microbiology term used to describe many colonies growing on a plate, on a slant, or in broth. A culture is referred to as a "pure culture" when there is only one type of organism in it

Question 39

Heavy or dominant growth

Answer 39

descriptor indicating the organism was present in high numbers or in all inoculum regions, dilutions, or concentrations

Question 40

incubate

Answer 40

to keep or sample over a period of time (often 12-48 hours) at a favorable temperature promoting growth, such as when creating a bacterial culture or growing an agar plate sample for colonies

Question 41

quadrant

Answer 41

an area on an agar plate, estimated by eye to be 1/4 of the total surface area

Question 42

scant growth

Answer 42

descriptor indicating the organisms was present in low numbers or only in certain inoculum regions, dilutions, or concentrations

Question 43

streak

Answer 43

inoculation of a surface performed by dragging a loop in a bac and forth motion across agar, resulting in the distribution and dilution of the microbial sample

Question 44

vegetative cell

Answer 44

a metabolically active and growing cell

Question 45

Subculturing of a bacterial sample is the most commonly used method for

Answer 45

obtaining pure cultures of bacterial species from mixed microbial populations.

Question 46

Specialized materials used for subculturing include

Answer 46

nutrient agar slants. At ~50°C, the melted liquid agar can be set at an angle along the side of a bacterial culture tube. When agar reaches room temperature, it forms into the solid state in a wedge shape at the top and solid against the tube walls at the bottom.

Question 47

Subculture isolation techniques are used to

Answer 47

grow microorganisms when pure culture of a single species is necessary, such as in clinical laboratories when identifying organisms causing disease states, or when assessing purity of a sample.

Question 48

inoculating needle

Answer 48

Because the size of the inoculating loop could damage the agar, the loop section can be removed, leaving a straight piece of wire only and is referred to as an "inoculating needle." The needle tip can be used to accurately acquire small amounts of bacterial sample by touching the needle point (in place of the loop) to the colony and then transferring to the medium for dispersal.

Question 49

When a bacterial sample is inoculated into the butt of an agar slant tube, it is commonly referred to as

Answer 49

a "stab".

Question 50

Can you be certain that you made a successful transfer if your sterile broth is turbid after incubation?

Answer 50

No, the broth will be turbid if it is correctly inoculated, but also if it was contaminated during the inoculation procedure. Reason: If the broth is turbid, it simply indicates that bacteria are growing in the tube. However, you do not know what species are present, so it is still possible that you may have incorrectly contaminated the broth during the transfer.