Microbiology Lab Final Exam Latest Update
2025-2026 200 Questions and 100% Verified
Correct Answers Guaranteed A+
5 stages of biofilm development - CORRECT ANSWER: 1. Reversible attachment =
cells attach and detach from the surface
2. Irreversible attachment = cell irreversible attaches to surface via cell adhesion
structures like pili
3. Maturation I
4. Maturation II = during 3 and 4, the biofilm becomes encased in an extracellular matrix
aka slime
5. Release = some of the cells within the biofilm are released and are planktoic and can
remain free or attach elsewhere to start new biofilm
A gram stain... - CORRECT ANSWER: -Discovered by Hans Christian Gram
-Differentiates bacteria based on thickness of peptidoglycan layer (not the
presence/absence of OM)
Acidophiles - CORRECT ANSWER: -bacteria that grow at a pH of 0-5.5
Alkalophiles - CORRECT ANSWER: -organisms that grow at a pH of 8-11.5
Amount of powder required to prepare TSA - CORRECT ANSWER: 40g/L or
40g/1000mL
-given volume needed
-set up ratios and cross multiply
Antiseptics - CORRECT ANSWER: chemical agents that are typically used on living
tissue to inhibit microbial growth/remove microbes
,-not sterilants
araC - CORRECT ANSWER: -gene encoding the AraC regulator that is derived from the
arabinose catabolism operon
-in the presence of arabinose, araC interacts w/ the sugar and binds to the promoter
region upstream of arabinose catabolism genes so organism can utilize the sugar...
BUT the pGLO plasmid only has the regulator and the gfp gene that replaced the genes
for arabinose catabolism.
-Binding of arabinose-activated AraC results in activation of gfp gene expression
Are biofilms typically composed of one or many types of organisms? - CORRECT
ANSWER: many
Bacterial culture medium - CORRECT ANSWER: -an artificial substrate used to support
the growth of bacteria in the lab
-supplies all essential macronutrients (C, N, O, H, P, S), micronutrients (Mg, Fe, K, Ca,
Zn, etc.) and growth factors
Bactericidal - CORRECT ANSWER: -agent that kills bacteria
Bacteriostatic - CORRECT ANSWER: -agent that inhibits growth of bacteria, but doesnt
kill
Biofilms vs planktonic cells - CORRECT ANSWER: -in lab bacteria grown in liquid
culture float around freely in the medium= planktonic cells
-In nature, bacteria often attach to a surface and form a biofilm: the growth of a
microbial community on a surface
bla - CORRECT ANSWER: -B-lactamase gene
-product of this gene provides resistance to ampicillin.
,-B-lactamase is an extracellular enzyme that acts on the B-lactam ring structure found
in ampicillin
Black precipitate in the agar - CORRECT ANSWER: Sulfur reduction, H2S produced
Blood Agar
DIFFERENTIAL - CORRECT ANSWER: -differential
-blood
-Differentiates based on type of hemolysis. alpha-hemolysis (partial destruction of
RBCs, greenish color may develop around colonies), Beta-hemolysis (complete
destruction of RBCs, zone of clearance surrounds colony), and Gamma-hemolysis
(non-hemolytic)
Blood Agar
ENRICHMENT - CORRECT ANSWER: -enrichment
-blood
-Enhances growth of fastidious bacteria (pathogens)
Cannot differentiate between a bactericidal and bacteriostatic antibiotic - CORRECT
ANSWER: ...
Capsule stain - CORRECT ANSWER: -capsule stain is a negative stain
-which means that the specimen (capsules) remain unstained and the background is
black. Cells are pink
Carbohydrate fermenter: - CORRECT ANSWER: -acidic by products produced (lactic
acid, acetic acid) will turn the medium yellow
, Catalase test, What is catalase? - CORRECT ANSWER: -catalase is an enzyme
produced by bacteria to detoxify hydrogen peroxide to water and oxygen gas. Hydrogen
is one of the more reactive oxygen species generated during aerobic metabolism.
-Differentiates between Staphylococcus species (catalase producers) and
streptococcus species (catalase non-producers)
-rapid bubbling after addition of H2O2= production of O2 gas, positive test, catalase
producer
Citrate test
-media used, what are you testing for?, Expected pos/neg results - CORRECT
ANSWER: -tests the ability of organisms to utilize citrate as a carbon source
-requires enzyme citrate permease, a transport proteins
-organisms on citrate convert ammonim dihydrogen phosphate (nitrogen source) to
ammonium and ammonium hydroxide
-ammonium products from citrate utilization change pH from neutral to alkaline
-pH indicator=bromthymol blue, green at neutral pH, so green medium when
uninoculated
--positive test, citrate producer=growth with deep blue color
--negative result, non citrate utilizer=little to no growth and no color change
Complex medium - CORRECT ANSWER: nutrients are added to the medium in the form
of animal/plant extracts
Cracks in or lifting of agar - CORRECT ANSWER: Gas production due to fermentation
Defined medium - CORRECT ANSWER: nutrients are added to the medium in the form
of pure chemicals
DF - CORRECT ANSWER: -dilution factor, no units
DF= (volume added in mL/total volume in mL) X DF of previous tube
2025-2026 200 Questions and 100% Verified
Correct Answers Guaranteed A+
5 stages of biofilm development - CORRECT ANSWER: 1. Reversible attachment =
cells attach and detach from the surface
2. Irreversible attachment = cell irreversible attaches to surface via cell adhesion
structures like pili
3. Maturation I
4. Maturation II = during 3 and 4, the biofilm becomes encased in an extracellular matrix
aka slime
5. Release = some of the cells within the biofilm are released and are planktoic and can
remain free or attach elsewhere to start new biofilm
A gram stain... - CORRECT ANSWER: -Discovered by Hans Christian Gram
-Differentiates bacteria based on thickness of peptidoglycan layer (not the
presence/absence of OM)
Acidophiles - CORRECT ANSWER: -bacteria that grow at a pH of 0-5.5
Alkalophiles - CORRECT ANSWER: -organisms that grow at a pH of 8-11.5
Amount of powder required to prepare TSA - CORRECT ANSWER: 40g/L or
40g/1000mL
-given volume needed
-set up ratios and cross multiply
Antiseptics - CORRECT ANSWER: chemical agents that are typically used on living
tissue to inhibit microbial growth/remove microbes
,-not sterilants
araC - CORRECT ANSWER: -gene encoding the AraC regulator that is derived from the
arabinose catabolism operon
-in the presence of arabinose, araC interacts w/ the sugar and binds to the promoter
region upstream of arabinose catabolism genes so organism can utilize the sugar...
BUT the pGLO plasmid only has the regulator and the gfp gene that replaced the genes
for arabinose catabolism.
-Binding of arabinose-activated AraC results in activation of gfp gene expression
Are biofilms typically composed of one or many types of organisms? - CORRECT
ANSWER: many
Bacterial culture medium - CORRECT ANSWER: -an artificial substrate used to support
the growth of bacteria in the lab
-supplies all essential macronutrients (C, N, O, H, P, S), micronutrients (Mg, Fe, K, Ca,
Zn, etc.) and growth factors
Bactericidal - CORRECT ANSWER: -agent that kills bacteria
Bacteriostatic - CORRECT ANSWER: -agent that inhibits growth of bacteria, but doesnt
kill
Biofilms vs planktonic cells - CORRECT ANSWER: -in lab bacteria grown in liquid
culture float around freely in the medium= planktonic cells
-In nature, bacteria often attach to a surface and form a biofilm: the growth of a
microbial community on a surface
bla - CORRECT ANSWER: -B-lactamase gene
-product of this gene provides resistance to ampicillin.
,-B-lactamase is an extracellular enzyme that acts on the B-lactam ring structure found
in ampicillin
Black precipitate in the agar - CORRECT ANSWER: Sulfur reduction, H2S produced
Blood Agar
DIFFERENTIAL - CORRECT ANSWER: -differential
-blood
-Differentiates based on type of hemolysis. alpha-hemolysis (partial destruction of
RBCs, greenish color may develop around colonies), Beta-hemolysis (complete
destruction of RBCs, zone of clearance surrounds colony), and Gamma-hemolysis
(non-hemolytic)
Blood Agar
ENRICHMENT - CORRECT ANSWER: -enrichment
-blood
-Enhances growth of fastidious bacteria (pathogens)
Cannot differentiate between a bactericidal and bacteriostatic antibiotic - CORRECT
ANSWER: ...
Capsule stain - CORRECT ANSWER: -capsule stain is a negative stain
-which means that the specimen (capsules) remain unstained and the background is
black. Cells are pink
Carbohydrate fermenter: - CORRECT ANSWER: -acidic by products produced (lactic
acid, acetic acid) will turn the medium yellow
, Catalase test, What is catalase? - CORRECT ANSWER: -catalase is an enzyme
produced by bacteria to detoxify hydrogen peroxide to water and oxygen gas. Hydrogen
is one of the more reactive oxygen species generated during aerobic metabolism.
-Differentiates between Staphylococcus species (catalase producers) and
streptococcus species (catalase non-producers)
-rapid bubbling after addition of H2O2= production of O2 gas, positive test, catalase
producer
Citrate test
-media used, what are you testing for?, Expected pos/neg results - CORRECT
ANSWER: -tests the ability of organisms to utilize citrate as a carbon source
-requires enzyme citrate permease, a transport proteins
-organisms on citrate convert ammonim dihydrogen phosphate (nitrogen source) to
ammonium and ammonium hydroxide
-ammonium products from citrate utilization change pH from neutral to alkaline
-pH indicator=bromthymol blue, green at neutral pH, so green medium when
uninoculated
--positive test, citrate producer=growth with deep blue color
--negative result, non citrate utilizer=little to no growth and no color change
Complex medium - CORRECT ANSWER: nutrients are added to the medium in the form
of animal/plant extracts
Cracks in or lifting of agar - CORRECT ANSWER: Gas production due to fermentation
Defined medium - CORRECT ANSWER: nutrients are added to the medium in the form
of pure chemicals
DF - CORRECT ANSWER: -dilution factor, no units
DF= (volume added in mL/total volume in mL) X DF of previous tube
