Bacteria Questions and Answers

Q: Nutrient agar is prepared by addition of

Correct answer: 3% agar in nutrient brothAgar is added at about 2-3% to set nutrient broth into a solid plate. Less than that gives a soft or semi-solid medium, used for motility testing; more would make the gel needlessly hard and hard to pour. Agar itself is not a nutrient - almost no bacterium can digest it, which is precisely why it is used as the gelling agent.

Q: Living microorganisms are studied using the

Correct answer: hanging drop techniqueThe hanging drop keeps the organisms alive and suspended in liquid under a cover slip over a cavity slide, so their true motility can be watched. Staining methods all begin by fixing - that is, killing - the cells, so they can never show movement.

Q: The material being tested contains

Correct answer: unknown antigenThe material being tested - a specimen from the patient or a culture - supplies the unknown antigen, and it is identified by reacting it against a diagnostic serum of known antibody.

Q: For adsorption, viruses use

Correct answer: Specific receptorsAdsorption is the first step of infection: a protein on the virus surface binds a specific receptor molecule on the host cell. Which receptor a virus recognises is what determines its host range and its tissue tropism - HIV binds CD4, so it infects helper T cells.

Q: This is analogous to mesosomes of bacteria

Correct answer: Mitochondria of eukaryotesThe mesosome is an infolding of the bacterial plasma membrane, long regarded as the seat of the respiratory enzymes - hence the comparison with the mitochondrion, which performs that role in eukaryotes.

Q: Negative result of the complement fixation reaction is expressed in

Correct answer: complete haemolysisA negative result means antigen and antibody did not correspond, so no complex formed and the complement was not fixed. It is still free when the indicator system is added, and it lyses the sensitised red cells - complete haemolysis, giving a clear red solution.

Q: Volutin granules are demonstrated by

Correct answer: Loeffler’s techniqueVolutin (metachromatic) granules are polyphosphate stores, and they stain a different colour from the rest of the cell with methylene blue - the metachromasia that gives them their name. Loeffler’s alkaline methylene blue is the classic method, and Neisser’s stain is used for the same purpose in Corynebacterium diphtheriae.

Q: The organ of locomotion of bacteria is

Correct answer: flagellaFlagella are the organelles of motility: a rotary motor in the membrane, driven by the proton-motive force, spins the helical filament like a propeller. Fimbriae are for attachment, and capsules and slime layers for protection.

Q: Which of this bacteria is resistant to penicillin as it lacks a cell wall?

Correct answer: MycoplasmasPenicillin blocks the cross-linking of peptidoglycan, so it can only act on a cell that is building a wall. Mycoplasmas have none - only a sterol-strengthened membrane - so the drug has nothing to attack. Spirochaetes, cyanobacteria and bdellovibrios all have walls.

21.

Nutrient agar is prepared by addition of

A.0% agar in nutrient broth
B.3% agar in nutrient broth
C.5% agar in nutrient broth
D.10% agar in nutrient broth

Answer: B

Correct answer: 3% agar in nutrient broth

Agar is added at about 2-3% to set nutrient broth into a solid plate. Less than that gives a soft or semi-solid medium, used for motility testing; more would make the gel needlessly hard and hard to pour. Agar itself is not a nutrient - almost no bacterium can digest it, which is precisely why it is used as the gelling agent.

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22.

Living microorganisms are studied using the

A.hanging drop technique
B.Gram’ s technique
C.Burri’ s technique
D.Morozov’s technique

Answer: A

Correct answer: hanging drop technique

The hanging drop keeps the organisms alive and suspended in liquid under a cover slip over a cavity slide, so their true motility can be watched. Staining methods all begin by fixing - that is, killing - the cells, so they can never show movement.

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23.

The material being tested contains

A.unknown antigen
B.unknown antibody
C.known antigen
D.known antibody

Answer: A

Correct answer: unknown antigen

The material being tested - a specimen from the patient or a culture - supplies the unknown antigen, and it is identified by reacting it against a diagnostic serum of known antibody.

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24.

For adsorption, viruses use

A.Specific receptors
B.Lysozyme
C.The mechanism called viropexia
D.The synthetic machinery of host cell

Answer: A

Correct answer: Specific receptors

Adsorption is the first step of infection: a protein on the virus surface binds a specific receptor molecule on the host cell. Which receptor a virus recognises is what determines its host range and its tissue tropism - HIV binds CD4, so it infects helper T cells.

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25.

This is analogous to mesosomes of bacteria

A.Golgi apparatus of eukaryotes
B.Lysosomes of eukaryotes
C.Mitochondria of eukaryotes
D.None of the above

Answer: C

Correct answer: Mitochondria of eukaryotes

The mesosome is an infolding of the bacterial plasma membrane, long regarded as the seat of the respiratory enzymes - hence the comparison with the mitochondrion, which performs that role in eukaryotes.

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26.

Negative result of the complement fixation reaction is expressed in

A.complete inhibition of haemolysis
B.complete haemolysis
C.haemagglutination
D.inhibition of haemagglutination

Answer: B

Correct answer: complete haemolysis

A negative result means antigen and antibody did not correspond, so no complex formed and the complement was not fixed. It is still free when the indicator system is added, and it lyses the sensitised red cells - complete haemolysis, giving a clear red solution.

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27.

Volutin granules are demonstrated by

A.Ozeshki’s staining
B.Burri’s technique
C.Loeffler’s technique
D.Morozov’s staining

Answer: C

Correct answer: Loeffler’s technique

Volutin (metachromatic) granules are polyphosphate stores, and they stain a different colour from the rest of the cell with methylene blue - the metachromasia that gives them their name. Loeffler’s alkaline methylene blue is the classic method, and Neisser’s stain is used for the same purpose in Corynebacterium diphtheriae.

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28.

The organ of locomotion of bacteria is

A.capsule
B.flagella
C.slime
D.fimbriae

Answer: B

Correct answer: flagella

Flagella are the organelles of motility: a rotary motor in the membrane, driven by the proton-motive force, spins the helical filament like a propeller. Fimbriae are for attachment, and capsules and slime layers for protection.

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29.

Which of this bacteria is resistant to penicillin as it lacks a cell wall?

A.Spirochetes
B.Cyanobacteria
C.Mycoplasmas
D.Bdellovibrios

Answer: C

Correct answer: Mycoplasmas

Penicillin blocks the cross-linking of peptidoglycan, so it can only act on a cell that is building a wall. Mycoplasmas have none - only a sterol-strengthened membrane - so the drug has nothing to attack. Spirochaetes, cyanobacteria and bdellovibrios all have walls.

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30.

Hemolytic serum for complement fixation reaction is obtained in the following manner

A.rabbits are immunized by suspension of sheep erythrocytes
B.sheep are immunized by suspension of rabbits erythrocytes
C.guinea pig are immunized by suspension of sheep erythrocytes
D.rabbits are immunized by suspension of guinea pig erythrocytes

Answer: A

Correct answer: rabbits are immunized by suspension of sheep erythrocytes

Haemolytic serum is anti-sheep-red-cell antibody, and it is raised by injecting rabbits with sheep erythrocytes. The rabbit serum is then heated to destroy its own complement, so that the only complement in the final test is the one being measured.

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