Bacteria Questions and Answers

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.

Q: Dark ground microscopy is used for detection of

Correct answer: spirochetesDark-ground (dark-field) microscopy lights the specimen obliquely so that only scattered light enters the objective, making a very thin unstained object shine against a black background. It is the standard way of seeing Treponema pallidum, which is too slender for ordinary bright-field work and stains poorly.

Q: Which of the following is true about the viral envelope?

Correct answer: All the aboveAll three are true of the viral envelope: it is derived from a host cell membrane as the virus buds out; it is therefore lipoprotein in nature; and it carries projecting spikes (peplomers) of virus-coded glycoprotein, which are what bind the receptor on the next cell. Being lipid, it is destroyed by soap and by ether - which is why enveloped viruses are the easier ones to disinfect.

Q: Killed corpuscular vaccines contain

Correct answer: inactivated bacteriaA killed corpuscular vaccine contains whole bacteria inactivated by heat or chemicals. Nothing multiplies, so it is safe and stable but generally needs a larger dose and booster injections. The old typhoid, cholera and whooping cough vaccines were of this kind.

Q: Monoclonal antibodies are used in

Correct answer: All of the aboveMonoclonal antibodies are used for all three: as therapeutic agents, since a single specificity can be directed at one target; for the identification of cells and tissues, as in typing leukaemias by their surface markers; and, radiolabelled, for imaging, localising a tumour by where the antibody accumulates.

Q: Live vaccines contain

Correct answer: attenuated bacteriaA live vaccine contains organisms that have been attenuated - weakened by repeated passage or by mutation so that they multiply in the recipient without causing disease. Because they multiply, the dose is small and the immunity strong and long-lasting; the price is that they must be kept cold and are unsafe for the immunocompromised. BCG and oral polio are examples.

91.

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

92.

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

93.

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

94.

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

95.

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

96.

Dark ground microscopy is used for detection of

A.spirochetes
B.chlamydia
C.fungi
D.virus

Answer: A

Correct answer: spirochetes

Dark-ground (dark-field) microscopy lights the specimen obliquely so that only scattered light enters the objective, making a very thin unstained object shine against a black background. It is the standard way of seeing Treponema pallidum, which is too slender for ordinary bright-field work and stains poorly.

Discuss in Forum

97.

Which of the following is true about the viral envelope?

A.Derived from the host cell membrane
B.Lipoprotein in nature
C.Has projecting spikes on the surface
D.All the above.

Answer: D

Correct answer: All the above

All three are true of the viral envelope: it is derived from a host cell membrane as the virus buds out; it is therefore lipoprotein in nature; and it carries projecting spikes (peplomers) of virus-coded glycoprotein, which are what bind the receptor on the next cell. Being lipid, it is destroyed by soap and by ether - which is why enveloped viruses are the easier ones to disinfect.

Discuss in Forum

98.

Killed corpuscular vaccines contain

A.attenuated bacteria
B.immunogenic component of the bacteria
C.inactivated bacteria
D.inactivated toxin

Answer: C

Correct answer: inactivated bacteria

A killed corpuscular vaccine contains whole bacteria inactivated by heat or chemicals. Nothing multiplies, so it is safe and stable but generally needs a larger dose and booster injections. The old typhoid, cholera and whooping cough vaccines were of this kind.

Discuss in Forum

99.

Monoclonal antibodies are used in

A.Immunotherapy
B.Immunological identification of cells and tissues
C.Radioimmuno-imaging
D.All of the above

Answer: D

Correct answer: All of the above

Monoclonal antibodies are used for all three: as therapeutic agents, since a single specificity can be directed at one target; for the identification of cells and tissues, as in typing leukaemias by their surface markers; and, radiolabelled, for imaging, localising a tumour by where the antibody accumulates.

Discuss in Forum

100.

Live vaccines contain

A.attenuated bacteria
B.immunogenic component of the bacteria
C.inactivated bacteria
D.inactivated toxin

Answer: A

Correct answer: attenuated bacteria

A live vaccine contains organisms that have been attenuated - weakened by repeated passage or by mutation so that they multiply in the recipient without causing disease. Because they multiply, the dose is small and the immunity strong and long-lasting; the price is that they must be kept cold and are unsafe for the immunocompromised. BCG and oral polio are examples.

Discuss in Forum

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