MCB2010L FINAL EXAM 2024/2025 LATEST
VERSION
What is the application of the DNase test? - CORRECT ANSWER Used to distinguish
Serrati species (+) from Enterobacter species (-), Moraxella catarrhal is (+) from
Neisseria species (-), and Staphylococcus aureus (+) from other Staphylococcus
species (-).
How are results interpreted for the DNase test? - CORRECT ANSWER -Clearing in
agar (loss of green color around growth): DNase is present (+)
-No clearing in agar around growth: DNase is absent (-)
Hemolysis - CORRECT ANSWER Produces by several species of Gram-positive cocci.
Able to destroy red blood cells and hemoglobin.
What is blood agar? - CORRECT ANSWER Includes 5% blood (frequently sheep blood)
in a tryptic soy agar base. Allows differentiation of bacteria based on their ability to
hemolysis RBCs.
What are the major types of hemolysis? - CORRECT ANSWER -ß-hemolysis: complete
destruction of RBCs and hemoglobin; results in a clearing of the medium around the
colonies. (ex. Streptococcus pyogenic)
-∂-hemolysis: partial destruction of RBCs and produces a greenish discoloration of the
agar around the colonies. (ex. Streptococcus pneumonia)
-y-hemolysis: non-hemolysis and appears as simple growth with no change to the
medium
Streptomycin’s - CORRECT ANSWER Hemolysis produced by streptococci. Come in
two forms, type O and type S.
-Streptomycin O: oxygen labile and expresses maximal activity under anaerobic
conditions
-Streptomycin S: oxygen stable, but expresses itself optimally under anaerobic
conditions as well.
Stab-streak technique - CORRECT ANSWER Easiest method of providing an
environment favorable for streptomycin’s on blood agar. Blood agar plate is streaked for
isolation and then stabbed with a loop. The stabs encourage streptomycin activity
because of the reduced oxygen concentration of the subsurface environment.
What is the application of blood agar? - CORRECT ANSWER Used for isolation and
cultivation of many types of fastidious bacteria. Used to differentiate bacteria based on
their hemolytic characteristics, especially within the genera Streptococcus,
Enterococcus, and Aero coccus.
,How are results from the blood agar plate interpreted? - CORRECT ANSWER -Clearing
around growth: organism hemolysis RBCs completely; ß-hemolysis
-Greening around growth: organism hemolysis RBCs partially; ∂-hemolysis
-No change in the medium: organism does not hemolysis RBCs; no hemolysis
Bacitracin - CORRECT ANSWER Produced by Bacillus licheniformis; a powerful
peptide antibiotic that inhibits bacterial cell wall synthesis by interfering with transport of
peptidoglycan subunits across the cytoplasmic membrane. Effective only on bacteria
that have cell walls and are in the process of growing. In this test, any gone of clearing
10 mm or greater around the disk is interpreted as bacitracin susceptibility.
Novobiocin - CORRECT ANSWER Antibiotic produced by Streptomyces nevus. Related
to coumarone and interferes with ATPase activity associated with DNA gyrase, and
enzyme necessary during DNA replication. In this test, a 5 microgram disk should
produce a zone of clearing 16 mm or more for the organism to be considered
susceptible.
Opt chin - CORRECT ANSWER Antibiotic derived from quinine that interferes with ATP
synthase activity and ATP production in susceptible bacteria. A 6 mm disk (containing 5
micrograms of opt chin) should produce a zone of inhibition 14 mm or more for the
organism to be considered susceptible.
What are the applications of the bacitracin, novobiocin, and optochin tests? -
CORRECT ANSWER -Bacitracin test is used to differentiate and presumptively identify
ß-hemolytic group A streptococcus (Streptococcus pyogenic- bacitracin susceptible)
from other ß-hemolytic streptococci (bacitracin resistant). It also differentiates the genus
Staphylococcus (resistant) from the susceptible Micrococcus.
-Novobiocin test is used to differentiate coagulase-negative staphylococci. Most
frequently, it is used to presumptively identify the novobiocin-resistant Staphylococcus
saprophytic us.
-Opt chin test is used to presumptively differentiate Streptococcus pneumonia from
other ∂-hemolytic streptococci.
How are the results interpreted in the bacitracin test? - CORRECT ANSWER -Zone of
clearing greater than 10 mm or greater: organism is susceptible to bacitracin (S)
-Zone of clearing less than 10 mm: organism is resistant to bacitracin (R)
How are the results interpreted in the novobiocin test? - CORRECT ANSWER -Zone of
clearing 16 mm or greater: organism is susceptible to novobiocin (S)
-Zone of clearing less than 16 mm: organism is resistant to novobiocin (R)
How are the results interpreted in the opt chin test? - CORRECT ANSWER -Zone of
clearing 14 mm or greater: organism is susceptible to opt chin (S)
-Zone of clearing less than 14 m: organism is resistant to opt chin (R)
, What is MacConkey agar? - CORRECT ANSWER A commonly used selective and
differential medium containing lactose, bile salts, neutral red, and crystal violet.
What are the components of the MAC agar and what do they do? - CORRECT
ANSWER -Bile salts and crystal violent inhibit the growth of Gram-positive bacteria.
Formulations without crystal violet allow growth of Enterococcus and some species of
Staphylococcus, which ferment the lactose and appear pink on the medium.
-Neutral red dye is a pH indicator that is colorless above pH 6.8 and red at a pH less
than 6.8.
How does the neutral red dye react to determine a reaction? - CORRECT ANSWER
Organisms that ferment lactose to acid end-products lower the pH and their colonies
turn a pink to red color. On occasion, a pink to red bile precipitate will also form in the
agar due to the lowered ph. Lactose non-fermenters retain their normal colour or the
colour of the medium.
What is the application of the MAC agar? - CORRECT ANSWER Used to isolate and
differentiate members of the Enterobacteriaceae based on the ability to ferment lactose.
Variations of the standard MAC medium include MAC agar without crystal violet to allow
growth of Gram-positive cocci or MAC agar CS to control swarming bacteria (Proteus)
that interfere with other results.
How are results for MAC agar interpreted? - CORRECT ANSWER -Poor growth or no
growth: organism is inhibited by crystal violet and/or bile; Gram-positive
-Good growth: organism is not inhibited by crystal violet or bile; Gram-negative
-Pink to red growth with or without bile precipitate: organism produced acid from lactose
fermentation; probably coliform
-Growth is "colorless" (not red or pink): organism does not ferment lactose; no coliform
What is the electron transport chain (ETC)? - CORRECT ANSWER ETCs of aerobic
and facultative anaerobic bacteria are composed of molecules capable of accepting and
donating electrons as conditions dictate. As such, these molecules alternate between
the oxidized and reduced forms, passing electrons down the chain to the final electron
acceptor, oxygen. Energy lost by electrons in this sequential transfer is used to perform
oxidative phosphorylation (i.e., produce ATP from ADP).
Flavoprotein - CORRECT ANSWER in most cases, electrons in the aerobic ETC follow
the step-wise path to oxygen, but other paths can be followed and these result in toxic
forms of reduced oxygen. ETC carrier molecule called flavoprotein can bypass the next
carrier in the chain and transfer electrons directly to oxygen, which produces hydrogen
peroxide, a highly potent cellular toxin. FADH2 is capable of the same reaction. Even if
the electrons follow the complete ETC, another toxin, the superoxide radical (O2-), can
be produced in the final step because electrons can reduce oxygen one at a time and
sometimes it is released before it is completely reduced to H2O. H2O2 and O2- are
toxic because they oxidize biochemical and make them nonfunctional. Organisms that
produce them also have enzymes that can break them down.
VERSION
What is the application of the DNase test? - CORRECT ANSWER Used to distinguish
Serrati species (+) from Enterobacter species (-), Moraxella catarrhal is (+) from
Neisseria species (-), and Staphylococcus aureus (+) from other Staphylococcus
species (-).
How are results interpreted for the DNase test? - CORRECT ANSWER -Clearing in
agar (loss of green color around growth): DNase is present (+)
-No clearing in agar around growth: DNase is absent (-)
Hemolysis - CORRECT ANSWER Produces by several species of Gram-positive cocci.
Able to destroy red blood cells and hemoglobin.
What is blood agar? - CORRECT ANSWER Includes 5% blood (frequently sheep blood)
in a tryptic soy agar base. Allows differentiation of bacteria based on their ability to
hemolysis RBCs.
What are the major types of hemolysis? - CORRECT ANSWER -ß-hemolysis: complete
destruction of RBCs and hemoglobin; results in a clearing of the medium around the
colonies. (ex. Streptococcus pyogenic)
-∂-hemolysis: partial destruction of RBCs and produces a greenish discoloration of the
agar around the colonies. (ex. Streptococcus pneumonia)
-y-hemolysis: non-hemolysis and appears as simple growth with no change to the
medium
Streptomycin’s - CORRECT ANSWER Hemolysis produced by streptococci. Come in
two forms, type O and type S.
-Streptomycin O: oxygen labile and expresses maximal activity under anaerobic
conditions
-Streptomycin S: oxygen stable, but expresses itself optimally under anaerobic
conditions as well.
Stab-streak technique - CORRECT ANSWER Easiest method of providing an
environment favorable for streptomycin’s on blood agar. Blood agar plate is streaked for
isolation and then stabbed with a loop. The stabs encourage streptomycin activity
because of the reduced oxygen concentration of the subsurface environment.
What is the application of blood agar? - CORRECT ANSWER Used for isolation and
cultivation of many types of fastidious bacteria. Used to differentiate bacteria based on
their hemolytic characteristics, especially within the genera Streptococcus,
Enterococcus, and Aero coccus.
,How are results from the blood agar plate interpreted? - CORRECT ANSWER -Clearing
around growth: organism hemolysis RBCs completely; ß-hemolysis
-Greening around growth: organism hemolysis RBCs partially; ∂-hemolysis
-No change in the medium: organism does not hemolysis RBCs; no hemolysis
Bacitracin - CORRECT ANSWER Produced by Bacillus licheniformis; a powerful
peptide antibiotic that inhibits bacterial cell wall synthesis by interfering with transport of
peptidoglycan subunits across the cytoplasmic membrane. Effective only on bacteria
that have cell walls and are in the process of growing. In this test, any gone of clearing
10 mm or greater around the disk is interpreted as bacitracin susceptibility.
Novobiocin - CORRECT ANSWER Antibiotic produced by Streptomyces nevus. Related
to coumarone and interferes with ATPase activity associated with DNA gyrase, and
enzyme necessary during DNA replication. In this test, a 5 microgram disk should
produce a zone of clearing 16 mm or more for the organism to be considered
susceptible.
Opt chin - CORRECT ANSWER Antibiotic derived from quinine that interferes with ATP
synthase activity and ATP production in susceptible bacteria. A 6 mm disk (containing 5
micrograms of opt chin) should produce a zone of inhibition 14 mm or more for the
organism to be considered susceptible.
What are the applications of the bacitracin, novobiocin, and optochin tests? -
CORRECT ANSWER -Bacitracin test is used to differentiate and presumptively identify
ß-hemolytic group A streptococcus (Streptococcus pyogenic- bacitracin susceptible)
from other ß-hemolytic streptococci (bacitracin resistant). It also differentiates the genus
Staphylococcus (resistant) from the susceptible Micrococcus.
-Novobiocin test is used to differentiate coagulase-negative staphylococci. Most
frequently, it is used to presumptively identify the novobiocin-resistant Staphylococcus
saprophytic us.
-Opt chin test is used to presumptively differentiate Streptococcus pneumonia from
other ∂-hemolytic streptococci.
How are the results interpreted in the bacitracin test? - CORRECT ANSWER -Zone of
clearing greater than 10 mm or greater: organism is susceptible to bacitracin (S)
-Zone of clearing less than 10 mm: organism is resistant to bacitracin (R)
How are the results interpreted in the novobiocin test? - CORRECT ANSWER -Zone of
clearing 16 mm or greater: organism is susceptible to novobiocin (S)
-Zone of clearing less than 16 mm: organism is resistant to novobiocin (R)
How are the results interpreted in the opt chin test? - CORRECT ANSWER -Zone of
clearing 14 mm or greater: organism is susceptible to opt chin (S)
-Zone of clearing less than 14 m: organism is resistant to opt chin (R)
, What is MacConkey agar? - CORRECT ANSWER A commonly used selective and
differential medium containing lactose, bile salts, neutral red, and crystal violet.
What are the components of the MAC agar and what do they do? - CORRECT
ANSWER -Bile salts and crystal violent inhibit the growth of Gram-positive bacteria.
Formulations without crystal violet allow growth of Enterococcus and some species of
Staphylococcus, which ferment the lactose and appear pink on the medium.
-Neutral red dye is a pH indicator that is colorless above pH 6.8 and red at a pH less
than 6.8.
How does the neutral red dye react to determine a reaction? - CORRECT ANSWER
Organisms that ferment lactose to acid end-products lower the pH and their colonies
turn a pink to red color. On occasion, a pink to red bile precipitate will also form in the
agar due to the lowered ph. Lactose non-fermenters retain their normal colour or the
colour of the medium.
What is the application of the MAC agar? - CORRECT ANSWER Used to isolate and
differentiate members of the Enterobacteriaceae based on the ability to ferment lactose.
Variations of the standard MAC medium include MAC agar without crystal violet to allow
growth of Gram-positive cocci or MAC agar CS to control swarming bacteria (Proteus)
that interfere with other results.
How are results for MAC agar interpreted? - CORRECT ANSWER -Poor growth or no
growth: organism is inhibited by crystal violet and/or bile; Gram-positive
-Good growth: organism is not inhibited by crystal violet or bile; Gram-negative
-Pink to red growth with or without bile precipitate: organism produced acid from lactose
fermentation; probably coliform
-Growth is "colorless" (not red or pink): organism does not ferment lactose; no coliform
What is the electron transport chain (ETC)? - CORRECT ANSWER ETCs of aerobic
and facultative anaerobic bacteria are composed of molecules capable of accepting and
donating electrons as conditions dictate. As such, these molecules alternate between
the oxidized and reduced forms, passing electrons down the chain to the final electron
acceptor, oxygen. Energy lost by electrons in this sequential transfer is used to perform
oxidative phosphorylation (i.e., produce ATP from ADP).
Flavoprotein - CORRECT ANSWER in most cases, electrons in the aerobic ETC follow
the step-wise path to oxygen, but other paths can be followed and these result in toxic
forms of reduced oxygen. ETC carrier molecule called flavoprotein can bypass the next
carrier in the chain and transfer electrons directly to oxygen, which produces hydrogen
peroxide, a highly potent cellular toxin. FADH2 is capable of the same reaction. Even if
the electrons follow the complete ETC, another toxin, the superoxide radical (O2-), can
be produced in the final step because electrons can reduce oxygen one at a time and
sometimes it is released before it is completely reduced to H2O. H2O2 and O2- are
toxic because they oxidize biochemical and make them nonfunctional. Organisms that
produce them also have enzymes that can break them down.
