MICROBIOLOGY LAB FINAL EXAM
2026/2027 WITH OVER 100 QUESTIONS
AND CORRECT ANSWERS RATED A+
Transferring microorganisms from one growth medium to a fresh medium to keep them
alive, isolate them, or study them more easily.
Confluent growth
When bacteria grow on an agar plate so densely that the colonies merge together into
a continuous, uniform layer with no individual colonies visible.
Isolated Colony
a single, well-separated colony on the agar, not touching other colonies.
Stock culture
a long-term, maintained microbial culture that serves as the source for future
experiments.
Difference between BSL-1 and BSL-2 organisms
BSL-1 Organisms are not able to cause disease in immunocompetent humans
In relation to streak plates
A: first section, confluent growth
B: second section, confluent growth
C: third section, mostly confluent growth
D: fourth section, isolated colonies
Subculture
Colony forming unit
measurement used to estimate the number of viable (living) microorganisms in a
sample.
Know the key components of aseptic technique
Know the purpose of streak plating
Know when/why/ to use the different forms of media (plate, broth, slant)
Steak plating is used to
1) isolate an organism
2) form observable colonies to study morphology
Uses for the following:
Plate: used to obtain isolated colonies to determine colony morphology and to separate
a mixed culture
Broth: used to grow lots of microbes quickly, will only keep culture alive for a short time
(hours to days)
Slant: used to store microbes for months at a time, the low air-to-surface ratio allows for
longer storage time
The steps of gram staining
Inoculate org. on plate with controls -> let dry -> Fix org. with methanol -> Crystal Violet
dye (60sec) -> Iodine (60sec) -> Decolorizer (15-20sec) -> Safranin (60sec)
, -Remember to rinse between each stain
-Dry with special paper at the end or let air dry.
-Know how to interpret results
What is the purpose of each stain/chemical in gram staining?
-Methanol: chemically fixes org. to slide
-Crystal violet (primary stain): stains all cells purple
-Iodine (mordant): binds to crystal violet dye to "fix" it inside Gram + cells
-Decolorizer: Damages peptidoglycan layer in G- cells so the crystal violet can wash
away
-Safranin (counterstain): Stains gram neg. cells pink
Selective Media
Selective media inhibits the growth of some organisms while allowing others to
grow. Usually with salt*
Differential Media
Differential media allow multiple organisms to grow, but make them look
different based on the way they metabolize certain ingredients. Usually sugars*
Amino Acid Decarboxylation
►A single amino acid is added to the decarboxylase base medium
►After inoculation, the medium is overlaid with mineral oil to create an anaerobic
environment to promote fermentation
►Initially, the medium turns yellow due to glucose fermentation decreasing the medium
pH
►The low pH stimulates the production of decarboxylases and the organism
begins to breakdown the specific amino acid in the medium🡪 turns purple
Purple = Pos
Thioglycolate Broth
►Sodium thioglycollate is a reducing agent🡪 removes O2
►Small amount of agar🡪 prevents O2 diffusion into the medium
►Near opening of tube🡪 more oxygen (pink indicator)
►Bottom of tube🡪 no oxygen
Strict (obligate) aerobes
►Only grow in presence of oxygen
Facultative anaerobes
►Grow best with oxygen, but can also grow without oxygen
Aerotolerant anaerobes
►Grow equally well in presence or absence of oxygen (doesn't use O2)
Strict (obligate) anaerobes
BSL-2 organisms pose a moderate risk for infection, but are usually easily treated.
Pure Culture
a culture with one species of organism
mixed culture
a culture with more than one species of organism
isolated colony
►Doesn't use oxygen to grow/dies in presence of oxygen
Microaerophiles
2026/2027 WITH OVER 100 QUESTIONS
AND CORRECT ANSWERS RATED A+
Transferring microorganisms from one growth medium to a fresh medium to keep them
alive, isolate them, or study them more easily.
Confluent growth
When bacteria grow on an agar plate so densely that the colonies merge together into
a continuous, uniform layer with no individual colonies visible.
Isolated Colony
a single, well-separated colony on the agar, not touching other colonies.
Stock culture
a long-term, maintained microbial culture that serves as the source for future
experiments.
Difference between BSL-1 and BSL-2 organisms
BSL-1 Organisms are not able to cause disease in immunocompetent humans
In relation to streak plates
A: first section, confluent growth
B: second section, confluent growth
C: third section, mostly confluent growth
D: fourth section, isolated colonies
Subculture
Colony forming unit
measurement used to estimate the number of viable (living) microorganisms in a
sample.
Know the key components of aseptic technique
Know the purpose of streak plating
Know when/why/ to use the different forms of media (plate, broth, slant)
Steak plating is used to
1) isolate an organism
2) form observable colonies to study morphology
Uses for the following:
Plate: used to obtain isolated colonies to determine colony morphology and to separate
a mixed culture
Broth: used to grow lots of microbes quickly, will only keep culture alive for a short time
(hours to days)
Slant: used to store microbes for months at a time, the low air-to-surface ratio allows for
longer storage time
The steps of gram staining
Inoculate org. on plate with controls -> let dry -> Fix org. with methanol -> Crystal Violet
dye (60sec) -> Iodine (60sec) -> Decolorizer (15-20sec) -> Safranin (60sec)
, -Remember to rinse between each stain
-Dry with special paper at the end or let air dry.
-Know how to interpret results
What is the purpose of each stain/chemical in gram staining?
-Methanol: chemically fixes org. to slide
-Crystal violet (primary stain): stains all cells purple
-Iodine (mordant): binds to crystal violet dye to "fix" it inside Gram + cells
-Decolorizer: Damages peptidoglycan layer in G- cells so the crystal violet can wash
away
-Safranin (counterstain): Stains gram neg. cells pink
Selective Media
Selective media inhibits the growth of some organisms while allowing others to
grow. Usually with salt*
Differential Media
Differential media allow multiple organisms to grow, but make them look
different based on the way they metabolize certain ingredients. Usually sugars*
Amino Acid Decarboxylation
►A single amino acid is added to the decarboxylase base medium
►After inoculation, the medium is overlaid with mineral oil to create an anaerobic
environment to promote fermentation
►Initially, the medium turns yellow due to glucose fermentation decreasing the medium
pH
►The low pH stimulates the production of decarboxylases and the organism
begins to breakdown the specific amino acid in the medium🡪 turns purple
Purple = Pos
Thioglycolate Broth
►Sodium thioglycollate is a reducing agent🡪 removes O2
►Small amount of agar🡪 prevents O2 diffusion into the medium
►Near opening of tube🡪 more oxygen (pink indicator)
►Bottom of tube🡪 no oxygen
Strict (obligate) aerobes
►Only grow in presence of oxygen
Facultative anaerobes
►Grow best with oxygen, but can also grow without oxygen
Aerotolerant anaerobes
►Grow equally well in presence or absence of oxygen (doesn't use O2)
Strict (obligate) anaerobes
BSL-2 organisms pose a moderate risk for infection, but are usually easily treated.
Pure Culture
a culture with one species of organism
mixed culture
a culture with more than one species of organism
isolated colony
►Doesn't use oxygen to grow/dies in presence of oxygen
Microaerophiles
