Bacteria Questions and Answers

Q: Which of the following is a simple staining method

Correct answer: BurriA simple stain uses a single dye and shows shape and arrangement without distinguishing types of cell. Burri’s India-ink method is of that kind - strictly a negative stain, colouring the background rather than the cell. Gram, Neisser and Ziehl-Neelsen are all differential stains, using more than one reagent to separate one group of organisms from another.

Q: The covalent bond which links the cell walls of gram-positive bacteria containing two modified sugars - N - acetylmuramic acid (NAM) and N-acetyl glucosamine (NAG) is

Correct answer: 1,4-glycosidic bondThe glycan backbone is an alternating chain of NAM and NAG joined by β-1,4-glycosidic bonds - the same linkage as in cellulose and chitin. It is precisely this bond that lysozyme hydrolyses, which is why tears and saliva can lyse many bacteria.

Q: The function of an adjuvant in a vaccine is

Correct answer: antigenicityAn adjuvant makes the antigen more immunogenic: it holds the antigen at the injection site so that it is released slowly, and it provokes a local inflammatory response that draws in and activates antigen-presenting cells. The result is a stronger and longer-lasting response to the same amount of antigen.

Q: Gram-positive microorganisms appear

Correct answer: violet colorGram-positive cells keep the primary stain, so they appear violet or purple. The safranin counterstain is applied afterwards but is masked by the darker dye already held.

Q: Active immunity is not acquired by

Correct answer: immunoglobulin transferReceiving ready-made immunoglobulin gives passive immunity: the recipient’s own immune system never responds, so no memory is left and the protection fades within weeks. Active immunity is what the body builds for itself - after an infection, a subclinical infection, or a vaccination.

Q: Differential media contain all of the following EXCEPT

Correct answer: Substances that inhibit microorganismsA differential medium contains a basal medium, the substrate in question (often a sugar) and an indicator to reveal what has been done to it - it lets everything grow and tells the colonies apart. Inhibitory substances belong to a selective medium, whose purpose is the opposite: to stop unwanted organisms growing at all.

Q: The spore has

Correct answer: all of the aboveThe spore is built in layers: an inner membrane round the core, a cortex of modified peptidoglycan between two membranes, and an outer keratin-like coat of protein - with an exosporium outside that in some species. Each layer contributes to its extraordinary resistance.

Q: Lysis reaction is a

Correct answer: all of the aboveA lysis reaction is antibody plus complement dissolving a cell, and it is named after whatever is dissolved: haemolysis of red cells, spirochaetolysis of spirochaetes, vibriolysis of vibrios. The mechanism is the same in each - the membrane attack complex of complement.

Q: H antigen is a

Correct answer: flagellar antigenH is the flagellar antigen, from the German Hauch, the spreading film that motile organisms make on a plate. It is protein - flagellin - and heat labile, unlike the O antigen, which is polysaccharide and heat stable.

Q: Chlamydias are

Correct answer: All the aboveChlamydiae are non-motile, obligate intracellular parasites that cannot be grown on cell-free media - they must be cultured in living cells, because they cannot make their own ATP and depend on the host’s. That energy dependence is what defines them.

91.

Which of the following is a simple staining method

A.Gram
B.Neisser
C.Ziehl-Neelsen
D.Burri

Answer: D

Correct answer: Burri

A simple stain uses a single dye and shows shape and arrangement without distinguishing types of cell. Burri’s India-ink method is of that kind - strictly a negative stain, colouring the background rather than the cell. Gram, Neisser and Ziehl-Neelsen are all differential stains, using more than one reagent to separate one group of organisms from another.

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92.

The covalent bond which links the cell walls of gram-positive bacteria containing two modified sugars - N - acetylmuramic acid (NAM) and N-acetyl glucosamine (NAG) is

A.glycosidic bond
B.1,4-glycosidic bond
C.1,6-glycosidic bond
D.glycosidic bond

Answer: B

Correct answer: 1,4-glycosidic bond

The glycan backbone is an alternating chain of NAM and NAG joined by β-1,4-glycosidic bonds - the same linkage as in cellulose and chitin. It is precisely this bond that lysozyme hydrolyses, which is why tears and saliva can lyse many bacteria.

Discuss in Forum

93.

The function of an adjuvant in a vaccine is

A.distribution
B.absorption
C.antigenicity
D.metabolism

Answer: C

Correct answer: antigenicity

An adjuvant makes the antigen more immunogenic: it holds the antigen at the injection site so that it is released slowly, and it provokes a local inflammatory response that draws in and activates antigen-presenting cells. The result is a stronger and longer-lasting response to the same amount of antigen.

Discuss in Forum

94.

Gram-positive microorganisms appear

A.violet color
B.green color
C.pink-red color
D.black color

Answer: A

Correct answer: violet color

Gram-positive cells keep the primary stain, so they appear violet or purple. The safranin counterstain is applied afterwards but is masked by the darker dye already held.

Discuss in Forum

95.

Active immunity is not acquired by

A.infection
B.vaccination
C.immunoglobulin transfer
D.subclinical infection

Answer: C

Correct answer: immunoglobulin transfer

Receiving ready-made immunoglobulin gives passive immunity: the recipient’s own immune system never responds, so no memory is left and the protection fades within weeks. Active immunity is what the body builds for itself - after an infection, a subclinical infection, or a vaccination.

Discuss in Forum

96.

Differential media contain all of the following EXCEPT

A.Basal medium
B.Substances that inhibit microorganisms
C.Sugar concerned
D.Indicator

Answer: B

Correct answer: Substances that inhibit microorganisms

A differential medium contains a basal medium, the substrate in question (often a sugar) and an indicator to reveal what has been done to it - it lets everything grow and tells the colonies apart. Inhibitory substances belong to a selective medium, whose purpose is the opposite: to stop unwanted organisms growing at all.

Discuss in Forum

97.

The spore has

A.an inner membrane
B.an outer keratin-like coat
C.two peptidoglycan layers
D.all of the above

Answer: D

Correct answer: all of the above

The spore is built in layers: an inner membrane round the core, a cortex of modified peptidoglycan between two membranes, and an outer keratin-like coat of protein - with an exosporium outside that in some species. Each layer contributes to its extraordinary resistance.

Discuss in Forum

98.

Lysis reaction is a

A.spirochetolysis
B.haemolysis
C.vibrionolysis
D.all of the above

Answer: D

Correct answer: all of the above

A lysis reaction is antibody plus complement dissolving a cell, and it is named after whatever is dissolved: haemolysis of red cells, spirochaetolysis of spirochaetes, vibriolysis of vibrios. The mechanism is the same in each - the membrane attack complex of complement.

Discuss in Forum

99.

H antigen is a

A.somatic antigen
B.capsular antigen
C.flagellar antigen
D.virulent antigen

Answer: C

Correct answer: flagellar antigen

H is the flagellar antigen, from the German Hauch, the spreading film that motile organisms make on a plate. It is protein - flagellin - and heat labile, unlike the O antigen, which is polysaccharide and heat stable.

Discuss in Forum

100.

Chlamydias are

A.non motile
B.can’ t be grown on cell - free media
C.obligately parasitic
D.All the above

Answer: D

Correct answer: All the above

Chlamydiae are non-motile, obligate intracellular parasites that cannot be grown on cell-free media - they must be cultured in living cells, because they cannot make their own ATP and depend on the host’s. That energy dependence is what defines them.

Discuss in Forum

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