Q.1 Which bacterial structure is primarily responsible for motility?
Pili
Flagella
Capsule
Cell wall
Explanation - Flagella are whip-like structures that allow bacteria to move in liquid environments, aiding in chemotaxis.
Correct answer is: Flagella
Q.2 Gram-negative bacteria have which characteristic feature?
Thick peptidoglycan layer
Outer membrane containing lipopolysaccharides
Teichoic acids in cell wall
No cell wall
Explanation - Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane that contains lipopolysaccharides, which contribute to their pathogenicity.
Correct answer is: Outer membrane containing lipopolysaccharides
Q.3 Which bacterium is known to cause tuberculosis?
Escherichia coli
Staphylococcus aureus
Mycobacterium tuberculosis
Salmonella typhi
Explanation - Mycobacterium tuberculosis is an acid-fast bacillus responsible for causing tuberculosis, primarily affecting the lungs.
Correct answer is: Mycobacterium tuberculosis
Q.4 What is the function of bacterial plasmids?
Protein synthesis
DNA replication
Antibiotic resistance and gene transfer
Energy production
Explanation - Plasmids are small, circular DNA molecules that can carry genes for antibiotic resistance and can be transferred between bacteria via conjugation.
Correct answer is: Antibiotic resistance and gene transfer
Q.5 Which bacteria are classified as Gram-positive cocci in clusters?
Streptococcus
Staphylococcus
Neisseria
Enterococcus
Explanation - Staphylococci appear as spherical cells arranged in grape-like clusters and are Gram-positive.
Correct answer is: Staphylococcus
Q.6 Endospores are primarily formed by which bacterial genera?
Bacillus and Clostridium
Escherichia and Salmonella
Streptococcus and Staphylococcus
Neisseria and Moraxella
Explanation - Endospores are highly resistant structures formed by Bacillus and Clostridium species to survive extreme conditions.
Correct answer is: Bacillus and Clostridium
Q.7 Which bacterial component triggers a strong immune response as an endotoxin?
Lipopolysaccharide
Peptidoglycan
Capsule
Flagella
Explanation - Lipopolysaccharides (LPS) in the outer membrane of Gram-negative bacteria act as endotoxins and can trigger fever and shock.
Correct answer is: Lipopolysaccharide
Q.8 What type of bacteria require oxygen to grow?
Obligate anaerobes
Facultative anaerobes
Obligate aerobes
Microaerophiles
Explanation - Obligate aerobes need oxygen for growth because they rely on aerobic respiration for energy production.
Correct answer is: Obligate aerobes
Q.9 Which bacterium is the most common cause of urinary tract infections?
Escherichia coli
Staphylococcus aureus
Klebsiella pneumoniae
Pseudomonas aeruginosa
Explanation - Escherichia coli is responsible for about 70–95% of community-acquired urinary tract infections.
Correct answer is: Escherichia coli
Q.10 Which method is used to classify bacteria based on their staining properties?
Gram staining
Acid-fast staining
Endospore staining
Capsule staining
Explanation - Gram staining differentiates bacteria into Gram-positive and Gram-negative based on their cell wall structure.
Correct answer is: Gram staining
Q.11 Listeria monocytogenes is primarily transmitted through:
Airborne droplets
Contaminated food
Vector-borne transmission
Direct contact with skin lesions
Explanation - Listeria monocytogenes is a foodborne pathogen often transmitted via unpasteurized dairy products and ready-to-eat meats.
Correct answer is: Contaminated food
Q.12 Which of the following bacteria are acid-fast?
Mycobacterium
Staphylococcus
Escherichia
Clostridium
Explanation - Mycobacteria have a high lipid content in their cell wall, retaining carbol fuchsin dye during acid-fast staining.
Correct answer is: Mycobacterium
Q.13 Which bacterial shape is rod-like?
Coccus
Bacillus
Spirillum
Vibrio
Explanation - Bacillus bacteria are rod-shaped, while cocci are spherical and spirilla are spiral-shaped.
Correct answer is: Bacillus
Q.14 Quorum sensing in bacteria is related to:
Movement toward nutrients
Regulation of gene expression based on population density
Spore formation
Cell wall synthesis
Explanation - Quorum sensing allows bacteria to coordinate behavior like biofilm formation or virulence factor expression according to cell population.
Correct answer is: Regulation of gene expression based on population density
Q.15 Which bacterium causes whooping cough?
Bordetella pertussis
Haemophilus influenzae
Streptococcus pneumoniae
Neisseria meningitidis
Explanation - Bordetella pertussis produces toxins that damage the respiratory epithelium, leading to characteristic paroxysmal cough.
Correct answer is: Bordetella pertussis
Q.16 Which bacterial enzyme breaks down hydrogen peroxide?
Catalase
Oxidase
Urease
Coagulase
Explanation - Catalase converts hydrogen peroxide into water and oxygen, protecting bacteria from oxidative damage.
Correct answer is: Catalase
Q.17 Which bacteria are known for their ability to form biofilms on medical devices?
Pseudomonas aeruginosa
Escherichia coli
Listeria monocytogenes
Clostridium difficile
Explanation - Pseudomonas aeruginosa can attach to surfaces and produce a biofilm, making infections difficult to treat.
Correct answer is: Pseudomonas aeruginosa
Q.18 Which genus of bacteria is primarily responsible for dental caries?
Streptococcus
Staphylococcus
Bacillus
Clostridium
Explanation - Streptococcus mutans metabolizes sugars to produce acids that demineralize tooth enamel, leading to cavities.
Correct answer is: Streptococcus
Q.19 Which of the following bacteria is a common cause of food poisoning from improperly stored meats?
Clostridium perfringens
Escherichia coli
Listeria monocytogenes
Salmonella typhi
Explanation - Clostridium perfringens forms spores that survive cooking, then germinate in warm conditions to produce toxins causing gastroenteritis.
Correct answer is: Clostridium perfringens
Q.20 Which bacterial structure helps evade phagocytosis?
Capsule
Flagella
Pili
Ribosomes
Explanation - The bacterial capsule prevents recognition and engulfment by immune cells, aiding in immune evasion.
Correct answer is: Capsule
Q.21 Which bacterium is associated with peptic ulcers?
Helicobacter pylori
Escherichia coli
Staphylococcus aureus
Clostridium difficile
Explanation - H. pylori colonizes the stomach lining, producing urease and toxins that damage gastric mucosa, leading to ulcers.
Correct answer is: Helicobacter pylori
Q.22 Which type of horizontal gene transfer involves direct transfer of DNA between bacterial cells?
Transformation
Transduction
Conjugation
Replication
Explanation - Conjugation involves direct cell-to-cell contact, often through pili, allowing transfer of plasmids or other DNA elements.
Correct answer is: Conjugation
Q.23 Which bacterium is the causative agent of diphtheria?
Corynebacterium diphtheriae
Clostridium tetani
Bacillus anthracis
Listeria monocytogenes
Explanation - C. diphtheriae produces diphtheria toxin that inhibits protein synthesis, causing severe respiratory disease.
Correct answer is: Corynebacterium diphtheriae
Q.24 Which test is used to differentiate Staphylococcus aureus from other Staphylococci?
Coagulase test
Catalase test
Oxidase test
Urease test
Explanation - S. aureus produces coagulase enzyme, which clots plasma, distinguishing it from coagulase-negative staphylococci.
Correct answer is: Coagulase test
Q.25 Which bacteria are obligate intracellular pathogens?
Rickettsia and Chlamydia
Escherichia and Salmonella
Bacillus and Clostridium
Staphylococcus and Streptococcus
Explanation - Rickettsia and Chlamydia require host cells for replication because they cannot produce enough energy on their own.
Correct answer is: Rickettsia and Chlamydia