Bacteria Questions and Answers

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

Correct answer: complete inhibition of haemolysisA positive result means the antigen and antibody did correspond, so the complement was fixed by their complex. None is left for the indicator system, the red cells stay intact, and they settle as a button - no haemolysis. It is an inversion that catches people out: no lysis means the test is positive.

Q: The spore protects the genomic DNA from

Correct answer: all of the aboveThe endospore protects its DNA against heat, chemicals and radiation alike. Its defences are the dehydrated core, the calcium dipicolinate that stabilises the DNA, the small acid-soluble proteins that coat it, and the thick cortex and coats outside. This is why boiling will not sterilise and autoclaving is required.

Q: Strict anaerobes lack which of the following enzymes?

Correct answer: All the aboveOxygen metabolism produces superoxide and hydrogen peroxide, and three enzymes normally deal with them: superoxide dismutase, catalase and peroxidase. Strict anaerobes lack them, so these products accumulate and destroy the cell - which is why oxygen is lethal to such organisms.

Q: This about cell wall of gram-positive bacteria is true

Correct answer: All of the aboveAll three describe the gram-positive wall: it is built of many layers of peptidoglycan, is much thicker than the gram-negative wall, and contains teichoic acids threaded through it. Those layers are what hold the crystal violet-iodine complex against decolourisation.

Q: What is a cluster of polar flagella called?

Correct answer: LophotrichousThe prefixes describe the arrangement: lophotrichous is a tuft of several flagella at one pole; monotrichous a single one; amphitrichous flagella at both poles; peritrichous flagella all over the surface.

Q: Ziehl-Neelsen staining consist of

Correct answer: 3 stagesZiehl-Neelsen has three steps: carbol fuchsin applied with heat, decolourisation with acid-alcohol, and a methylene blue counterstain. Acid-fast organisms such as mycobacteria keep the fuchsin, because their waxy mycolic acid wall resists the acid-alcohol.

Q: A diagnosticum contains

Correct answer: known antigenA diagnosticum is a standardised preparation of known antigen - killed bacteria, or antigen coated on carrier particles - used to detect the corresponding antibody in a patient’s serum. It is the mirror image of a diagnostic serum.

Q: What is responsible for the endotoxin activity of LPS

Correct answer: lipid ALipid A is the endotoxin. Released when gram-negative cells lyse, it triggers macrophages to pour out cytokines, producing fever, hypotension and, in quantity, septic shock. The O antigen and core polysaccharide are antigenic but not themselves toxic.

Q: Reduction of virulence is known as

Correct answer: attenuationAttenuation is the reduction of virulence while the organism is kept alive - achieved by repeated subculture, growth under unfavourable conditions, or passage through an unnatural host. It is the basis of live vaccines such as BCG. The opposite, enhancing virulence by passage through a susceptible host, is called exaltation.

Q: Reinfection is

Correct answer: subsequent infection by the same organismReinfection is a later infection by the same organism, after the first has resolved. It is distinct from a relapse, in which the original infection was never cleared and flares up again.

11.

Positive result of the complement fixation reaction is expressed in

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

Answer: A

Correct answer: complete inhibition of haemolysis

A positive result means the antigen and antibody did correspond, so the complement was fixed by their complex. None is left for the indicator system, the red cells stay intact, and they settle as a button - no haemolysis. It is an inversion that catches people out: no lysis means the test is positive.

Discuss in Forum

12.

The spore protects the genomic DNA from

A.intense heat
B.chemical agents
C.radiation
D.all of the above

Answer: D

Correct answer: all of the above

The endospore protects its DNA against heat, chemicals and radiation alike. Its defences are the dehydrated core, the calcium dipicolinate that stabilises the DNA, the small acid-soluble proteins that coat it, and the thick cortex and coats outside. This is why boiling will not sterilise and autoclaving is required.

Discuss in Forum

13.

Strict anaerobes lack which of the following enzymes?

A.Catalase
B.Peroxidase
C.Superoxide dismutase
D.All the above

Answer: D

Correct answer: All the above

Oxygen metabolism produces superoxide and hydrogen peroxide, and three enzymes normally deal with them: superoxide dismutase, catalase and peroxidase. Strict anaerobes lack them, so these products accumulate and destroy the cell - which is why oxygen is lethal to such organisms.

Discuss in Forum

14.

This about cell wall of gram-positive bacteria is true

A.cell wall comprises of many layers
B.the cell wall is thicker than the associated gram-negative bacteria
C.Cell wall comprises of teichoic acids
D.All of the above

Answer: D

Correct answer: All of the above

All three describe the gram-positive wall: it is built of many layers of peptidoglycan, is much thicker than the gram-negative wall, and contains teichoic acids threaded through it. Those layers are what hold the crystal violet-iodine complex against decolourisation.

Discuss in Forum

15.

What is a cluster of polar flagella called?

A.Petritrichous
B.Monotrichous
C.Amphitrichous
D.Lophotrichous

Answer: D

Correct answer: Lophotrichous

The prefixes describe the arrangement: lophotrichous is a tuft of several flagella at one pole; monotrichous a single one; amphitrichous flagella at both poles; peritrichous flagella all over the surface.

Discuss in Forum

16.

Ziehl-Neelsen staining consist of

A.2 stages
B.4 stages
C.3 stages
D.5 stages

Answer: C

Correct answer: 3 stages

Ziehl-Neelsen has three steps: carbol fuchsin applied with heat, decolourisation with acid-alcohol, and a methylene blue counterstain. Acid-fast organisms such as mycobacteria keep the fuchsin, because their waxy mycolic acid wall resists the acid-alcohol.

Discuss in Forum

17.

A diagnosticum contains

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

Answer: C

Correct answer: known antigen

A diagnosticum is a standardised preparation of known antigen - killed bacteria, or antigen coated on carrier particles - used to detect the corresponding antibody in a patient’s serum. It is the mirror image of a diagnostic serum.

Discuss in Forum

18.

What is responsible for the endotoxin activity of LPS

A.lipid A
B.O antigen
C.core polysaccharide
D.all of the above

Answer: A

Correct answer: lipid A

Lipid A is the endotoxin. Released when gram-negative cells lyse, it triggers macrophages to pour out cytokines, producing fever, hypotension and, in quantity, septic shock. The O antigen and core polysaccharide are antigenic but not themselves toxic.

Discuss in Forum

19.

Reduction of virulence is known as

A.attenuation
B.initiation
C.exaltation
D.inhibition

Answer: A

Correct answer: attenuation

Attenuation is the reduction of virulence while the organism is kept alive - achieved by repeated subculture, growth under unfavourable conditions, or passage through an unnatural host. It is the basis of live vaccines such as BCG. The opposite, enhancing virulence by passage through a susceptible host, is called exaltation.

Discuss in Forum

20.

Reinfection is

A.initial infection with organism in host
B.subsequent infection by the same organism
C. situation, when patient suffering from a disease and new infection is set up from external source
D.all of the above

Answer: B

Correct answer: subsequent infection by the same organism

Reinfection is a later infection by the same organism, after the first has resolved. It is distinct from a relapse, in which the original infection was never cleared and flares up again.

Discuss in Forum

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