Bacteria Questions and Answers

Q: Which ONE of the following statements about E.coli is NOT true ?

The statement that is not true is E.coli was the first disease- causing bacterium identified by Robert Koch.The first bacterium Koch proved to cause a disease was Bacillus anthracis, the agent of anthrax, in 1876, in the work that led to Koch's postulates; he later identified the tubercle bacillus and the cholera vibrio. E. coli was described by Theodor Escherich in 1885.The other statements are true. E. coli is a normal member of the human gut microbiota, it is beneficial (it competes with pathogens and makes vitamin K), and enterohaemorrhagic strains such as O157:H7 cause bloody diarrhoea.

Q: Which one of the following molecules is the master regulator of the planktonic-surface transition in Pseudomonas aeruginosa during biofilm formation?

The master regulator is cyclic dimeric guanosine monophosphate (c-di-GMP).In Pseudomonas aeruginosa c-di-GMP is made by diguanylate cyclases and broken down by phosphodiesterases. A high level switches the cell from swimming (planktonic) to the sessile state: flagellar motility is turned down and the production of exopolysaccharides such as Pel and Psl, which build the biofilm matrix, is turned up. A low level favours dispersal.Cyclic thiolactone peptides are quorum-sensing signals of Gram-positive staphylococci, cyclic triadenylate is a second messenger of bacterial antiphage defence systems, and cycloheximide is an antibiotic that blocks eukaryotic protein synthesis. None controls this transition.

Q: Legionella sp. multiply intracellularly within ....................., just as they do within human monocytes and macrophages.

Legionella multiplies within amoeba.In natural and man-made water systems, Legionella pneumophila lives and multiplies inside free-living amoebae such as Acanthamoeba and Naegleria. The way it avoids digestion inside the amoeba is the same strategy it uses in human alveolar macrophages and monocytes, which is how it causes Legionnaires' disease.Bacteria, fungi and plants are not its natural hosts; the protozoan host is what lets it persist in cooling towers and water tanks.

Q: Heterocyst from cyanobacteria contains enzyme :

Heterocysts contain Nitrogenase.Heterocysts are specialised thick-walled cells of filamentous cyanobacteria such as Anabaena and Nostoc. They lack the oxygen-evolving photosystem II, and their wall slows the entry of oxygen, which protects the oxygen-sensitive enzyme nitrogenase that fixes atmospheric nitrogen.Pectinase and cellulase break down plant cell-wall polysaccharides, and phosphorylase breaks down storage glucans; none of these is the special enzyme of the heterocyst.

Q: Helicobacter pylori uses urease to counteract a chemical defense in the human organ in which it lives. This chemical defense is :

The chemical defense is hydrochloric acid.Helicobacter pylori lives in the stomach, where parietal cells secrete hydrochloric acid that keeps gastric pH near 1 to 2. The bacterium produces large amounts of urease, which splits urea into ammonia and carbon dioxide. The ammonia neutralises acid around the cell, letting it survive and reach the mucus layer.Lysozyme is an enzyme in tears and saliva that attacks peptidoglycan, superoxide radicals are made by phagocytes, and sebum is the oily secretion of the skin. Urease is not a defence against any of these.

Q: Mycoplasmas, rickettsiae, and chlamydiae are :

Mycoplasmas, rickettsiae and chlamydiae are small bacteria.All three are prokaryotes. Mycoplasmas are the smallest free-living bacteria and lack a cell wall. Rickettsiae and chlamydiae are small obligate intracellular bacteria that cannot grow outside host cells, which once led them to be confused with viruses.They have both DNA and RNA, ribosomes and their own metabolism, and are inhibited by antibiotics such as tetracycline, so they are not viruses. They are not fungi or protozoa, both of which are eukaryotes.

Q: Which bacterial structure enables adherence to host tissue surfaces ?

Correct answer: FimbriaeFimbriae, also called common pili, are short surface filaments whose adhesins bind receptors on host cells, and that attachment is often the first step of infection. Flagella provide motility and the capsule resists phagocytosis.

Q: Salt agar is a

Correct answer: selective mediaSalt (mannitol salt) agar contains about 7.5% sodium chloride, which inhibits most bacteria while staphylococci tolerate it. Suppressing the unwanted flora so that one group can grow is exactly what makes a medium selective.

Q: Which one of these has a Chinese letter arrangement?

Correct answer: Corynebacterium diphtheriaeCorynebacterium diphtheriae divides by snapping fission: the cells bend sharply apart but stay joined at one end, giving the V and L shapes described as a Chinese-letter or palisade arrangement. It is a useful diagnostic clue in a stained smear.

Q: LPS (endotoxin) consist of

Correct answer: all of the aboveLipopolysaccharide has three parts: lipid A, anchored in the outer membrane and responsible for the endotoxic activity; the core polysaccharide; and the O antigen, the variable chain of repeating sugars that projects outwards and determines the serotype.

Which ONE of the following statements about E.coli is NOT true ?

A.E.coli was the first disease- causing bacterium identified by Robert Koch
B.E.coli is part of the normal microbiota of humans
C.Certain E.coli strains can cause bloody diarrohea
D.E.coli is beneficial to human

Exam Year(s)

GATE Life Sciences - 2012,

Answer: A

The statement that is not true is E.coli was the first disease- causing bacterium identified by Robert Koch.

The first bacterium Koch proved to cause a disease was Bacillus anthracis, the agent of anthrax, in 1876, in the work that led to Koch's postulates; he later identified the tubercle bacillus and the cholera vibrio. E. coli was described by Theodor Escherich in 1885.

The other statements are true. E. coli is a normal member of the human gut microbiota, it is beneficial (it competes with pathogens and makes vitamin K), and enterohaemorrhagic strains such as O157:H7 cause bloody diarrhoea.

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Which one of the following molecules is the master regulator of the planktonic-surface transition in Pseudomonas aeruginosa during biofilm formation?

A.Cyclic thiolactone
B.Cyclic dimeric guanosine monophosphate
C.Cyclic triadenylate
D.Cyclohexamide

Exam Year(s)

GATE Life Sciences - 2026,

Answer: B

The master regulator is cyclic dimeric guanosine monophosphate (c-di-GMP).

In Pseudomonas aeruginosa c-di-GMP is made by diguanylate cyclases and broken down by phosphodiesterases. A high level switches the cell from swimming (planktonic) to the sessile state: flagellar motility is turned down and the production of exopolysaccharides such as Pel and Psl, which build the biofilm matrix, is turned up. A low level favours dispersal.

Cyclic thiolactone peptides are quorum-sensing signals of Gram-positive staphylococci, cyclic triadenylate is a second messenger of bacterial antiphage defence systems, and cycloheximide is an antibiotic that blocks eukaryotic protein synthesis. None controls this transition.

Discuss in Forum

Legionella sp. multiply intracellularly within ....................., just as they do within human monocytes and macrophages.

A.amoeba
B.bacteria
C.fungi
D.plants

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: A

Legionella multiplies within amoeba.

In natural and man-made water systems, Legionella pneumophila lives and multiplies inside free-living amoebae such as Acanthamoeba and Naegleria. The way it avoids digestion inside the amoeba is the same strategy it uses in human alveolar macrophages and monocytes, which is how it causes Legionnaires' disease.

Bacteria, fungi and plants are not its natural hosts; the protozoan host is what lets it persist in cooling towers and water tanks.

Discuss in Forum

Heterocyst from cyanobacteria contains enzyme :

A.Pectinase
B.Cellulase
C.Nitrogenase
D.Phosphorylase

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: C

Heterocysts contain Nitrogenase.

Heterocysts are specialised thick-walled cells of filamentous cyanobacteria such as Anabaena and Nostoc. They lack the oxygen-evolving photosystem II, and their wall slows the entry of oxygen, which protects the oxygen-sensitive enzyme nitrogenase that fixes atmospheric nitrogen.

Pectinase and cellulase break down plant cell-wall polysaccharides, and phosphorylase breaks down storage glucans; none of these is the special enzyme of the heterocyst.

Discuss in Forum

Helicobacter pylori uses urease to counteract a chemical defense in the human organ in which it lives. This chemical defense is :

A.Lysozyme
B.Hydrochloric acid
C.Superoxide radicals
D.Sebum

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: B

The chemical defense is hydrochloric acid.

Helicobacter pylori lives in the stomach, where parietal cells secrete hydrochloric acid that keeps gastric pH near 1 to 2. The bacterium produces large amounts of urease, which splits urea into ammonia and carbon dioxide. The ammonia neutralises acid around the cell, letting it survive and reach the mucus layer.

Lysozyme is an enzyme in tears and saliva that attacks peptidoglycan, superoxide radicals are made by phagocytes, and sebum is the oily secretion of the skin. Urease is not a defence against any of these.

Discuss in Forum

Mycoplasmas, rickettsiae, and chlamydiae are :

A.Types of fungi
B.Small bacteria
C.Species of protozoa
D.Forms of viruses

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: B

Mycoplasmas, rickettsiae and chlamydiae are small bacteria.

All three are prokaryotes. Mycoplasmas are the smallest free-living bacteria and lack a cell wall. Rickettsiae and chlamydiae are small obligate intracellular bacteria that cannot grow outside host cells, which once led them to be confused with viruses.

They have both DNA and RNA, ribosomes and their own metabolism, and are inhibited by antibiotics such as tetracycline, so they are not viruses. They are not fungi or protozoa, both of which are eukaryotes.

Discuss in Forum

Which bacterial structure enables adherence to host tissue surfaces ?

A.Flagella
B.Fimbriae
C.Capsule
D.Ribosomes

Answer: B

Correct answer: Fimbriae

Fimbriae, also called common pili, are short surface filaments whose adhesins bind receptors on host cells, and that attachment is often the first step of infection. Flagella provide motility and the capsule resists phagocytosis.

Discuss in Forum

Salt agar is a

A.differential media
B.enriched media
C.selective media
D.simple media

Answer: C

Correct answer: selective media

Salt (mannitol salt) agar contains about 7.5% sodium chloride, which inhibits most bacteria while staphylococci tolerate it. Suppressing the unwanted flora so that one group can grow is exactly what makes a medium selective.

Discuss in Forum

Which one of these has a Chinese letter arrangement?

A.Clostridium tetani
B.Mycobacterium tuberculosis
C.Bacillus anthracis
D.Corynebacterium diphtheriae

Answer: D

Correct answer: Corynebacterium diphtheriae

Corynebacterium diphtheriae divides by snapping fission: the cells bend sharply apart but stay joined at one end, giving the V and L shapes described as a Chinese-letter or palisade arrangement. It is a useful diagnostic clue in a stained smear.

Discuss in Forum

10.

LPS (endotoxin) consist of

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

Answer: D

Correct answer: all of the above

Lipopolysaccharide has three parts: lipid A, anchored in the outer membrane and responsible for the endotoxic activity; the core polysaccharide; and the O antigen, the variable chain of repeating sugars that projects outwards and determines the serotype.

Discuss in Forum

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