Q.1 Which of the following is a domain of life that includes bacteria?
Eukarya
Archaea
Bacteria
Protista
Explanation - The domain Bacteria comprises all true bacterial species.
Correct answer is: Bacteria
Q.2 What is the main difference between Gram-positive and Gram-negative bacteria?
Shape
Size
Cell wall thickness
Number of chromosomes
Explanation - Gram-positive bacteria have a thick peptidoglycan layer, while Gram-negative bacteria have a thin layer and an outer membrane.
Correct answer is: Cell wall thickness
Q.3 Which shape is NOT a common bacterial morphology?
Coccus
Bacillus
Spirilla
Oval
Explanation - Oval is a descriptive term for shape but not a recognized bacterial morphology category.
Correct answer is: Oval
Q.4 In a Gram stain, what color do Gram-positive bacteria appear?
Blue or purple
Pink or red
Green
No color
Explanation - Gram-positive bacteria retain the crystal violet stain, appearing blue or purple under the microscope.
Correct answer is: Blue or purple
Q.5 Which of the following is a spore-forming bacterial genus?
Staphylococcus
Streptococcus
Bacillus
Mycobacterium
Explanation - Bacillus species, such as B. subtilis, can form endospores for survival.
Correct answer is: Bacillus
Q.6 Which classification level is directly above genus?
Family
Species
Order
Class
Explanation - Taxonomic hierarchy: Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species.
Correct answer is: Family
Q.7 What is the name of the pigment that gives some bacteria a blue color?
Chlorophyll
Carotenoid
Menaquinone
Cyanin
Explanation - Cyanin pigments, such as cyanochromes, give certain bacteria a blue appearance.
Correct answer is: Cyanin
Q.8 Which of these bacteria is commonly found in the human gut?
Staphylococcus aureus
Escherichia coli
Pseudomonas aeruginosa
Clostridium difficile
Explanation - E. coli is a normal gut commensal, though some strains can be pathogenic.
Correct answer is: Escherichia coli
Q.9 What is the primary structural difference between a rod-shaped bacterium and a spherical one?
Nucleus
Plasmid count
Shape of cell
Number of cell walls
Explanation - Rod-shaped bacteria are elongated (bacilli) while spherical bacteria are cocci.
Correct answer is: Shape of cell
Q.10 Which of the following bacteria is a common cause of urinary tract infections?
Streptococcus pneumoniae
Neisseria gonorrhoeae
Enterococcus faecalis
Haemophilus influenzae
Explanation - Enterococcus faecalis frequently colonizes the urinary tract and can cause infections.
Correct answer is: Enterococcus faecalis
Q.11 Which of the following is an example of a gram-negative rod?
Staphylococcus aureus
Escherichia coli
Bacillus subtilis
Corynebacterium diphtheriae
Explanation - E. coli is a Gram-negative rod-shaped bacterium.
Correct answer is: Escherichia coli
Q.12 What type of bacterial cell division results in two genetically identical daughter cells?
Binary fission
Conjugation
Transformation
Transduction
Explanation - Binary fission is the common asexual replication method in bacteria.
Correct answer is: Binary fission
Q.13 Which of these statements best describes archaea?
They are a type of virus.
They have cell walls made of peptidoglycan.
They thrive in extreme environments.
They are the same as bacteria.
Explanation - Archaea are often found in extreme habitats like hot springs and acidic waters.
Correct answer is: They thrive in extreme environments.
Q.14 Which bacterial feature is associated with pathogenicity in many bacteria?
Motility flagella
Spore formation
Gram staining
Cell division method
Explanation - Motility can help bacteria colonize host tissues and evade immune responses.
Correct answer is: Motility flagella
Q.15 What is the main component of bacterial cell walls?
Chitin
Peptidoglycan
Lipid bilayer
Calcium carbonate
Explanation - Peptidoglycan provides strength and rigidity to bacterial cell walls.
Correct answer is: Peptidoglycan
Q.16 Which of the following is a gram-positive cocci found in clusters?
Streptococcus pyogenes
Staphylococcus aureus
Streptococcus pneumoniae
Enterococcus faecalis
Explanation - Staphylococcus species form grape-like clusters of cocci.
Correct answer is: Staphylococcus aureus
Q.17 Which term describes a bacterial group that can survive in oxygen-rich environments?
Anaerobes
Aerotolerant
Facultative
Microaerophiles
Explanation - Aerotolerant bacteria can tolerate oxygen but do not use it for respiration.
Correct answer is: Aerotolerant
Q.18 Which of the following bacterial shapes is spirally twisted?
Coccus
Spirillum
Bacillus
Lactobacillus
Explanation - Spirilla (or spiral-shaped) bacteria are helically twisted, such as Salmonella.
Correct answer is: Spirillum
Q.19 What is a key difference between bacterial endospores and bacterial cysts?
Endospores are eukaryotic.
Cysts are only formed by fungi.
Endospores are highly resistant, cysts are not.
Cysts have a cell wall, endospores do not.
Explanation - Endospores are dormant, resistant structures; cysts are generally less resistant.
Correct answer is: Endospores are highly resistant, cysts are not.
Q.20 Which of the following bacteria is known for causing the disease 'tuberculosis'?
Mycobacterium tuberculosis
Staphylococcus aureus
Bacillus subtilis
Clostridium botulinum
Explanation - Mycobacterium tuberculosis is the causative agent of tuberculosis.
Correct answer is: Mycobacterium tuberculosis
Q.21 In bacterial taxonomy, what does the term 'phyla' refer to?
Groups of species within a genus
The highest level of classification below domain
Specific strains within a species
The genetic material of bacteria
Explanation - Phyla are broad taxonomic categories grouping related classes of bacteria.
Correct answer is: The highest level of classification below domain
Q.22 Which of these bacterial genera is a typical member of the human gut microbiome?
Lactobacillus
Pseudomonas
Salmonella
Shigella
Explanation - Lactobacillus species are common commensals in the gastrointestinal tract.
Correct answer is: Lactobacillus
Q.23 Which of the following describes a 'facultative anaerobe'?
Uses oxygen exclusively
Uses oxygen or ferment
Never uses oxygen
Can only survive without oxygen
Explanation - Facultative anaerobes switch between aerobic respiration and fermentation.
Correct answer is: Uses oxygen or ferment
Q.24 What is the main function of bacterial flagella?
Attachment to surfaces
Energy production
Motility
DNA replication
Explanation - Flagella provide locomotion for many bacteria.
Correct answer is: Motility
Q.25 Which of the following is a correct statement about bacterial conjugation?
It involves transfer of DNA via a viral vector.
It is a form of asexual reproduction.
It requires direct cell-to-cell contact.
It only occurs in Gram-positive bacteria.
Explanation - Conjugation transfers plasmid DNA through a pilus between bacteria.
Correct answer is: It requires direct cell-to-cell contact.
Q.26 Which bacterial phylum is most commonly associated with nitrogen fixation?
Proteobacteria
Firmicutes
Actinobacteria
Cyanobacteria
Explanation - Cyanobacteria, also known as blue-green algae, perform photosynthesis and nitrogen fixation.
Correct answer is: Cyanobacteria
Q.27 Which of the following is NOT a characteristic of mycoplasma species?
Lack a cell wall
Small genome
Gram-positive stain
Can be cultured on rich media
Explanation - Mycoplasma do not retain the Gram stain because they lack a cell wall.
Correct answer is: Gram-positive stain
Q.28 What term is used for bacteria that are able to grow in the absence of oxygen?
Anaerobes
Aerobes
Microaerophiles
Facultatives
Explanation - Anaerobes can grow without oxygen, often using fermentation.
Correct answer is: Anaerobes
Q.29 Which of the following bacteria is commonly used as a model organism in genetics?
Escherichia coli
Staphylococcus aureus
Pseudomonas aeruginosa
Clostridium botulinum
Explanation - E. coli is a well-studied model for bacterial genetics and molecular biology.
Correct answer is: Escherichia coli
Q.30 Which bacterial shape is elongated and cylindrical?
Coccus
Spore
Bacillus
Vibrio
Explanation - Bacillus refers to rod-shaped bacteria.
Correct answer is: Bacillus
Q.31 Which of the following is a major difference between Gram-positive and Gram-negative bacteria?
Number of plasmids
Presence of outer membrane
Shape
Ability to form spores
Explanation - Gram-negative bacteria have an outer membrane; Gram-positive do not.
Correct answer is: Presence of outer membrane
Q.32 Which of these bacteria is a Gram-positive cocci that can cause strep throat?
Streptococcus pyogenes
Staphylococcus aureus
Escherichia coli
Neisseria meningitidis
Explanation - S. pyogenes is a Gram-positive coccus responsible for strep throat.
Correct answer is: Streptococcus pyogenes
Q.33 What is the term for a bacterial classification that groups species by their genetic similarity?
Phylogenetic classification
Morphological classification
Physiological classification
Ecological classification
Explanation - Phylogenetic classification organizes bacteria based on genetic relatedness.
Correct answer is: Phylogenetic classification
Q.34 Which of the following bacterial genera is known for producing the antibiotic penicillin?
Streptococcus
Bacillus
Penicillium
Clostridium
Explanation - Penicillium fungi produce penicillin; the question is a trick—bacteria do not.
Correct answer is: Penicillium
Q.35 Which of the following is a primary method for determining bacterial species?
DNA sequencing of 16S rRNA gene
Counting cell size under microscope
Testing for flagellar presence
Measuring colony color on agar
Explanation - Sequencing the 16S rRNA gene is a standard molecular method for bacterial identification.
Correct answer is: DNA sequencing of 16S rRNA gene
Q.36 Which bacterial group is characterized by a thick peptidoglycan layer and teichoic acids in their cell walls?
Gram-negative bacteria
Gram-positive bacteria
Mycoplasma
Archaea
Explanation - Gram-positive bacteria have a thick peptidoglycan layer and teichoic acids.
Correct answer is: Gram-positive bacteria
Q.37 Which of the following is a common laboratory technique to differentiate between bacterial species?
Gram staining
pH titration
Temperature measurement
Light scattering
Explanation - Gram staining differentiates bacteria into Gram-positive and Gram-negative groups.
Correct answer is: Gram staining
Q.38 Which bacterial genus is most associated with acne?
Propionibacterium
Staphylococcus
Streptococcus
Pseudomonas
Explanation - Propionibacterium acnes (now Cutibacterium acnes) colonizes hair follicles, causing acne.
Correct answer is: Propionibacterium
Q.39 What is the main function of bacterial plasmids?
Encodes ribosomal RNA
Contains essential genes for survival
Can carry antibiotic resistance genes
Produces cell wall proteins
Explanation - Plasmids are extra-chromosomal DNA that often carry accessory traits like antibiotic resistance.
Correct answer is: Can carry antibiotic resistance genes
Q.40 Which of the following bacteria is a spore-forming, Gram-positive rod that can cause food poisoning?
Bacillus cereus
Staphylococcus aureus
Escherichia coli
Listeria monocytogenes
Explanation - B. cereus forms spores and produces toxins leading to foodborne illness.
Correct answer is: Bacillus cereus
Q.41 Which of the following is true about bacterial cell walls?
All bacteria have identical cell walls
Gram-positive bacteria have an outer membrane
Gram-negative bacteria have a thicker peptidoglycan layer
Gram-negative bacteria possess an outer membrane
Explanation - Gram-negative bacteria have an outer membrane not present in Gram-positive cells.
Correct answer is: Gram-negative bacteria possess an outer membrane
Q.42 What is the most common shape of bacteria found in the human respiratory tract?
Cocci
Bacilli
Spirilla
Vibrio
Explanation - Many respiratory pathogens, like Streptococcus pneumoniae, are bacilli or cocci; the majority are cocci, but many bacilli like Haemophilus influenzae also colonize.
Correct answer is: Bacilli
Q.43 Which bacterial genus is known for its rod shape and ability to reduce nitrate to nitrogen gas?
Nitrosomonas
Pseudomonas
Clostridium
Bacillus
Explanation - Pseudomonas species are versatile, performing denitrification in various environments.
Correct answer is: Pseudomonas
Q.44 Which of the following statements best describes bacterial motility?
All bacteria move by gliding along surfaces
Flagella are the most common structure for bacterial movement
Motility is only found in Gram-positive bacteria
Bacteria move using cilia
Explanation - Flagella are common appendages that propel many bacteria.
Correct answer is: Flagella are the most common structure for bacterial movement
Q.45 Which of the following bacterial genera is not found in the human oral cavity?
Streptococcus
Actinomyces
Corynebacterium
Enterobacter
Explanation - Enterobacter species are typically gut bacteria, not commonly found in the mouth.
Correct answer is: Enterobacter
Q.46 What is a defining characteristic of the phylum Firmicutes?
They are all Gram-negative
They are all Gram-positive
They possess a cell membrane without cell wall
They are all spore-formers
Explanation - Firmicutes are predominantly Gram-positive bacteria.
Correct answer is: They are all Gram-positive
Q.47 Which bacterial process involves the uptake of naked DNA from the environment?
Conjugation
Transformation
Transduction
Replication
Explanation - Transformation is the natural uptake of free DNA by a bacterium.
Correct answer is: Transformation
Q.48 Which of the following is a typical environment for halophilic bacteria?
Freshwater lakes
High-salt lakes
Acidic hot springs
Oxygen-rich soils
Explanation - Halophilic bacteria thrive in environments with high salt concentration.
Correct answer is: High-salt lakes
Q.49 Which of the following is a common laboratory medium for growing Gram-positive bacteria?
MacConkey agar
Mannitol salt agar
Cetrimide agar
Congo red agar
Explanation - Mannitol salt agar is selective for Staphylococcus species (Gram-positive).
Correct answer is: Mannitol salt agar
Q.50 Which of these bacterial species is known to cause Lyme disease?
Borrelia burgdorferi
Escherichia coli
Staphylococcus aureus
Pseudomonas aeruginosa
Explanation - Borrelia burgdorferi is a spirochete transmitted by ticks.
Correct answer is: Borrelia burgdorferi
Q.51 Which of the following bacterial structures is involved in DNA replication initiation?
OriC
FtsZ
RecA
Cas9
Explanation - OriC is the origin of replication in bacterial chromosomes.
Correct answer is: OriC
Q.52 Which bacterial genus is known for causing tetanus?
Clostridium tetani
Staphylococcus aureus
Escherichia coli
Lactobacillus
Explanation - Clostridium tetani is the causative agent of tetanus.
Correct answer is: Clostridium tetani
Q.53 Which bacterial process is responsible for the horizontal transfer of genes between bacteria?
Replication
Transcription
Transformation
Translation
Explanation - Transformation allows bacteria to acquire new genetic traits from the environment.
Correct answer is: Transformation
Q.54 Which bacterial genus is commonly used in the dairy industry to produce yogurt?
Staphylococcus
Lactobacillus
Pseudomonas
Bacillus
Explanation - Lactobacillus species ferment lactose to lactic acid, creating yogurt.
Correct answer is: Lactobacillus
Q.55 Which of the following is a primary feature that differentiates Gram-negative bacteria from Gram-positive bacteria in terms of antibiotic resistance?
Presence of teichoic acids
Presence of an outer membrane
Ability to form spores
Size of ribosomes
Explanation - The outer membrane of Gram-negative bacteria can act as a barrier to many antibiotics.
Correct answer is: Presence of an outer membrane
Q.56 Which of the following bacterial families includes the species responsible for tetanus?
Enterobacteriaceae
Staphylococcaceae
Clostridiaceae
Streptococcaceae
Explanation - Clostridiaceae includes Clostridium tetani, the tetanus-causing organism.
Correct answer is: Clostridiaceae
Q.57 Which bacterial process involves the transfer of genetic material via a phage?
Conjugation
Transduction
Transformation
Replication
Explanation - Transduction is bacterial horizontal gene transfer mediated by bacteriophages.
Correct answer is: Transduction
Q.58 Which bacterial phylum is known for containing many of the gut commensal species?
Actinobacteria
Proteobacteria
Bacteroidetes
Firmicutes
Explanation - Bacteroidetes are abundant in the human gut microbiota.
Correct answer is: Bacteroidetes
Q.59 What is a distinguishing characteristic of the genus Vibrio?
Gram-positive cocci
Motile, curved rods
Spore-forming
Non-motile cocci
Explanation - Vibrio species are comma-shaped, Gram-negative rods that are motile.
Correct answer is: Motile, curved rods
Q.60 Which bacterial enzyme is critical for the synthesis of the bacterial cell wall?
DNA polymerase
Peptidoglycan synthase
RNA polymerase
Hexokinase
Explanation - Peptidoglycan synthase (penicillin-binding proteins) are essential for cell wall formation.
Correct answer is: Peptidoglycan synthase
Q.61 Which of the following is a Gram-negative rod that can cause urinary tract infections?
Escherichia coli
Streptococcus pyogenes
Corynebacterium diphtheriae
Staphylococcus aureus
Explanation - E. coli is the most common pathogen of UTIs and is Gram-negative.
Correct answer is: Escherichia coli
Q.62 Which of the following bacterial structures is a thin, flexible filament that can help bacteria attach to surfaces?
Cilia
Pili
Flagella
Spores
Explanation - Pili (fimbriae) are hair-like appendages that mediate attachment.
Correct answer is: Pili
Q.63 What is the main advantage of bacterial endospores?
They increase metabolic rate
They enable DNA replication
They provide resistance to harsh conditions
They allow motility
Explanation - Endospores are dormant forms that survive extreme heat, desiccation, etc.
Correct answer is: They provide resistance to harsh conditions
Q.64 Which bacterial species is a facultative anaerobe that is commonly found in the human mouth?
Streptococcus mutans
Bacillus subtilis
Clostridium perfringens
Neisseria meningitidis
Explanation - S. mutans is a facultative anaerobe that colonizes teeth and causes cavities.
Correct answer is: Streptococcus mutans
Q.65 Which of the following bacteria is known for producing the pigment pyocyanin?
Pseudomonas aeruginosa
Staphylococcus aureus
Escherichia coli
Bacillus anthracis
Explanation - P. aeruginosa secretes pyocyanin, giving cultures a blue-green color.
Correct answer is: Pseudomonas aeruginosa
Q.66 Which of the following bacterial groups is known for their ability to fix nitrogen in root nodules of legumes?
Rhizobium
Clostridium
Lactobacillus
Staphylococcus
Explanation - Rhizobium species form symbiotic root nodules that fix atmospheric nitrogen.
Correct answer is: Rhizobium
Q.67 What is a typical shape of the bacterium Mycoplasma?
Coccus
Bacillus
Spiral
Irregular
Explanation - Mycoplasma lack cell walls and have an irregular, pleomorphic shape.
Correct answer is: Irregular
Q.68 Which of the following bacteria is a Gram-positive coccus that forms chains?
Streptococcus agalactiae
Staphylococcus aureus
E. coli
Pseudomonas aeruginosa
Explanation - Streptococcus species produce chains of cocci.
Correct answer is: Streptococcus agalactiae
Q.69 Which of the following is NOT typically found in the normal skin flora?
Propionibacterium
Staphylococcus epidermidis
Streptococcus pyogenes
Cutibacterium acnes
Explanation - S. pyogenes is a pathogen, not a common skin commensal.
Correct answer is: Streptococcus pyogenes
Q.70 Which bacterial structure is responsible for the synthesis of ribosomal proteins?
Polysomes
Ribosomes
Transcription factors
Operons
Explanation - Ribosomes translate mRNA into proteins, assembling ribosomal proteins.
Correct answer is: Ribosomes
Q.71 Which of the following bacteria is a spore-forming pathogen that causes anthrax?
Bacillus anthracis
Clostridium botulinum
Staphylococcus aureus
Pseudomonas aeruginosa
Explanation - B. anthracis is a Gram-positive, spore-forming rod causing anthrax.
Correct answer is: Bacillus anthracis
Q.72 What is a key morphological difference between a spirochete and a coccus?
Presence of flagella
Shape (helical vs spherical)
Gram stain result
Spore formation
Explanation - Spirochetes are helical; cocci are spherical.
Correct answer is: Shape (helical vs spherical)
Q.73 Which of the following bacteria is known to cause meningitis in newborns?
Neisseria meningitidis
Escherichia coli
Staphylococcus aureus
Enterococcus faecalis
Explanation - E. coli is a common cause of neonatal meningitis.
Correct answer is: Escherichia coli
Q.74 Which bacterial group is most associated with producing bioluminescence?
Pseudomonas
Vibrio
Streptococcus
Lactobacillus
Explanation - Vibrio species, such as V. fischeri, produce light via bioluminescence.
Correct answer is: Vibrio
Q.75 What is the main advantage of bacterial conjugation over transformation?
No need for plasmids
Transfer of large DNA segments
Requires no cell contact
Occurs only in Gram-negative bacteria
Explanation - Conjugation can transfer large plasmids or chromosomal fragments between cells.
Correct answer is: Transfer of large DNA segments
Q.76 Which of the following bacterial genera is known for causing foodborne illness due to toxin production?
Salmonella
E. coli (EHEC)
Listeria monocytogenes
All of the above
Explanation - All these genera can cause foodborne illness via toxins.
Correct answer is: All of the above
Q.77 Which bacterial classification level groups organisms that share a common ancestor but are not closely related enough to be in the same genus?
Species
Family
Order
Genus
Explanation - Family includes related genera, sharing ancestry but distinct enough.
Correct answer is: Family
Q.78 Which bacterial species is a Gram-positive coccus that forms grape-like clusters?
Streptococcus pyogenes
Staphylococcus aureus
Lactobacillus acidophilus
Bacillus subtilis
Explanation - S. aureus forms clusters of cocci resembling grapes.
Correct answer is: Staphylococcus aureus
Q.79 Which bacterial process allows the incorporation of foreign DNA into the bacterial chromosome?
Transduction
Conjugation
Transformation
Replication
Explanation - Transformation involves uptake and incorporation of free DNA.
Correct answer is: Transformation
Q.80 What is the primary difference between a Gram-negative bacterium’s outer membrane and a Gram-positive bacterium’s cell wall?
Outer membrane contains lipopolysaccharide
Cell wall contains teichoic acids
Both have lipopolysaccharides
Gram-positive cells have an outer membrane
Explanation - Gram-negative outer membrane has LPS; Gram-positive lacks outer membrane.
Correct answer is: Outer membrane contains lipopolysaccharide
Q.81 Which of the following is a common symptom of bacterial meningitis?
Cough
Severe headache
Blurred vision
Joint pain
Explanation - Bacterial meningitis often presents with severe headache, fever, and neck stiffness.
Correct answer is: Severe headache
Q.82 Which bacterial genus is associated with the production of lactic acid in fermented foods?
Lactobacillus
Staphylococcus
Pseudomonas
Bacillus
Explanation - Lactobacillus ferments sugars to lactic acid, used in cheese and yogurt.
Correct answer is: Lactobacillus
Q.83 Which bacterial classification includes organisms such as Escherichia coli, Salmonella, and Shigella?
Enterobacteriaceae
Staphylococcaceae
Lactobacillaceae
Bacillaceae
Explanation - Enterobacteriaceae is a family of Gram-negative Enteric bacteria.
Correct answer is: Enterobacteriaceae
Q.84 Which of the following is a characteristic of obligate anaerobes?
They thrive in the presence of oxygen
They can survive in both aerobic and anaerobic conditions
They are killed by oxygen
They require oxygen for growth
Explanation - Obligate anaerobes cannot survive in oxygen-rich environments.
Correct answer is: They are killed by oxygen
Q.85 Which bacterial genus is known for its ability to oxidize sulfur compounds?
Thiosulfate-oxidizing bacteria
Clostridium
Streptococcus
Lactobacillus
Explanation - Certain bacteria oxidize sulfur for energy, e.g., Thiobacillus.
Correct answer is: Thiosulfate-oxidizing bacteria
Q.86 What is the most common site of infection for Streptococcus pneumoniae?
Respiratory tract
Skin
Gastrointestinal tract
Urinary tract
Explanation - S. pneumoniae often causes pneumonia and sinusitis.
Correct answer is: Respiratory tract
Q.87 Which of the following bacteria is Gram-positive, non-spore-forming, and can cause endocarditis?
Staphylococcus aureus
Escherichia coli
Pseudomonas aeruginosa
Listeria monocytogenes
Explanation - S. aureus can adhere to heart valves and cause endocarditis.
Correct answer is: Staphylococcus aureus
Q.88 Which bacterial phylum includes many photosynthetic bacteria?
Cyanobacteria
Actinobacteria
Firmicutes
Proteobacteria
Explanation - Cyanobacteria are photosynthetic, often called blue-green algae.
Correct answer is: Cyanobacteria
Q.89 Which bacterial genus is a common cause of urinary tract infections and produces urease?
Proteus mirabilis
Staphylococcus epidermidis
Lactobacillus acidophilus
Bacillus cereus
Explanation - Proteus species hydrolyze urea, leading to stone formation.
Correct answer is: Proteus mirabilis
Q.90 Which of the following bacterial structures is a thin, flexible filament that can help bacteria attach to surfaces?
Pili
Flagella
Spores
Teichoic acids
Explanation - Pili (fimbriae) allow bacteria to adhere to host cells and surfaces.
Correct answer is: Pili
Q.91 Which bacterial classification level is used to group bacteria that share common genetic markers, like 16S rRNA sequences?
Species
Genus
Family
Phylum
Explanation - Species are defined by genetic similarity, especially 16S rRNA.
Correct answer is: Species
Q.92 Which of the following bacteria is a Gram-negative, rod-shaped, non-spore-forming organism that causes gastroenteritis?
Salmonella enterica
Streptococcus pyogenes
Listeria monocytogenes
Bacillus cereus
Explanation - S. enterica is a non-spore-forming Gram-negative rod causing foodborne illness.
Correct answer is: Salmonella enterica
Q.93 Which bacterial process results in the exchange of DNA from a donor to a recipient cell via a sex pilus?
Conjugation
Transformation
Transduction
Replication
Explanation - Conjugation uses a sex pilus to transfer plasmids.
Correct answer is: Conjugation
Q.94 Which bacterial genus is known for its role in nitrogen fixation in legume root nodules?
Rhizobium
Bacillus
Staphylococcus
Escherichia
Explanation - Rhizobium forms symbiotic nodules fixing atmospheric nitrogen.
Correct answer is: Rhizobium
Q.95 Which of the following bacterial species is Gram-positive, spore-forming, and can produce botulinum toxin?
Clostridium botulinum
Bacillus cereus
Staphylococcus aureus
Escherichia coli
Explanation - C. botulinum is a Gram-positive, spore-forming pathogen producing botulinum toxin.
Correct answer is: Clostridium botulinum
Q.96 Which of the following is a key difference between Gram-negative and Gram-positive bacteria regarding antibiotic penetration?
Outer membrane provides barrier to some antibiotics
Peptidoglycan thickness blocks antibiotics
Gram-positive lack porin channels
Gram-negative lack cell walls
Explanation - The outer membrane of Gram-negative bacteria limits antibiotic entry.
Correct answer is: Outer membrane provides barrier to some antibiotics
Q.97 Which bacterial group is known to produce a bioluminescent glow in deep sea environments?
Vibrio fischeri
Escherichia coli
Streptococcus pyogenes
Bacillus subtilis
Explanation - V. fischeri produces light via luciferase, used by squid symbiosis.
Correct answer is: Vibrio fischeri
Q.98 Which bacterial species is a common cause of dental caries due to acid production?
Streptococcus mutans
Staphylococcus aureus
Bacillus subtilis
Pseudomonas aeruginosa
Explanation - S. mutans metabolizes sucrose to lactic acid, eroding tooth enamel.
Correct answer is: Streptococcus mutans
Q.99 Which bacterial classification level is used to group organisms that share a common ancestor but are not closely related enough to be in the same genus?
Species
Family
Order
Genus
Explanation - Family groups related genera under a common ancestry.
Correct answer is: Family
Q.100 Which bacterial process allows the transfer of DNA from a virus to a bacterial cell?
Transduction
Conjugation
Transformation
Replication
Explanation - Transduction uses bacteriophages to move DNA between bacteria.
Correct answer is: Transduction
Q.101 Which of the following bacterial genera is not typically found in the human gut microbiome?
Bacteroides
Firmicutes
Enterococcus
Pseudomonas
Explanation - Pseudomonas is an environmental bacterium, not a gut commensal.
Correct answer is: Pseudomonas
Q.102 What is the main advantage of bacterial spores over vegetative cells?
They grow faster
They can resist extreme heat and desiccation
They can reproduce via binary fission
They produce toxins
Explanation - Spores are highly resistant to harsh conditions.
Correct answer is: They can resist extreme heat and desiccation
Q.103 Which bacterial species is a common cause of pneumonia in children?
Streptococcus pneumoniae
Escherichia coli
Staphylococcus aureus
Pseudomonas aeruginosa
Explanation - S. pneumoniae is the most frequent cause of pediatric pneumonia.
Correct answer is: Streptococcus pneumoniae
Q.104 Which bacterial genus is known for causing tetanus when it produces tetanospasmin?
Clostridium tetani
Staphylococcus aureus
Escherichia coli
Bacillus subtilis
Explanation - C. tetani produces tetanospasmin causing the disease tetanus.
Correct answer is: Clostridium tetani
Q.105 Which bacterial process involves the uptake of naked DNA from the environment?
Transformation
Conjugation
Transduction
Replication
Explanation - Transformation is the natural uptake of free DNA by bacteria.
Correct answer is: Transformation
Q.106 Which bacterial genus is a Gram-negative, rod-shaped organism that produces a characteristic green pigment in culture?
Pseudomonas aeruginosa
Staphylococcus aureus
Escherichia coli
Bacillus subtilis
Explanation - P. aeruginosa secretes pyocyanin, giving a green pigment.
Correct answer is: Pseudomonas aeruginosa
Q.107 Which of the following bacteria is Gram-positive, forms endospores, and is often associated with food poisoning?
Bacillus cereus
Staphylococcus aureus
Escherichia coli
Pseudomonas aeruginosa
Explanation - B. cereus forms spores and can cause foodborne illness.
Correct answer is: Bacillus cereus
Q.108 Which bacterial species is commonly used in the production of industrial enzymes and is a model organism for Gram-positive bacteria?
Bacillus subtilis
Staphylococcus aureus
Escherichia coli
Pseudomonas putida
Explanation - B. subtilis is a model Gram-positive organism widely used in biotechnology.
Correct answer is: Bacillus subtilis
Q.109 Which bacterial genus is known for its ability to oxidize sulfur for energy, often found in marine environments?
Thiobacillus
Streptococcus
E. coli
Bacillus
Explanation - Thiobacillus oxidizes sulfide to sulfate, generating energy for growth.
Correct answer is: Thiobacillus
Q.110 What is the primary function of bacterial pili?
Motility
Attachment
DNA replication
Cell division
Explanation - Pili help bacteria attach to surfaces and host cells.
Correct answer is: Attachment
Q.111 Which of the following bacteria is a common cause of skin abscesses?
Staphylococcus aureus
Escherichia coli
Pseudomonas aeruginosa
Salmonella enterica
Explanation - S. aureus can invade skin layers, forming abscesses.
Correct answer is: Staphylococcus aureus
Q.112 Which bacterial classification includes organisms like Streptococcus and Neisseria?
Actinobacteria
Firmicutes
Proteobacteria
Bacillus
Explanation - Streptococcus and Neisseria are Gram-positive; Firmicutes is a major Gram-positive phylum.
Correct answer is: Firmicutes
Q.113 Which bacterial genus is a major cause of dental plaque formation?
Streptococcus mutans
Staphylococcus aureus
Bacillus cereus
Pseudomonas aeruginosa
Explanation - S. mutans ferments sucrose into acid, promoting plaque.
Correct answer is: Streptococcus mutans
Q.114 Which of the following bacteria is Gram-negative, rod-shaped, and a common cause of urinary tract infections?
Escherichia coli
Staphylococcus aureus
Bacillus subtilis
Pseudomonas aeruginosa
Explanation - E. coli is the most frequent cause of UTIs.
Correct answer is: Escherichia coli
Q.115 Which bacterial classification level is used to group species that share a common ancestor but are not closely related enough to be in the same genus?
Family
Order
Phylum
Species
Explanation - Family groups related genera sharing a common ancestor.
Correct answer is: Family
Q.116 Which bacterial genus is known for its role in nitrogen fixation within legume root nodules?
Rhizobium
Bacillus
Streptococcus
Escherichia
Explanation - Rhizobium forms symbiotic nodules fixing atmospheric nitrogen.
Correct answer is: Rhizobium
Q.117 Which bacterial process results in the exchange of plasmids between bacterial cells via a pilus?
Conjugation
Transformation
Transduction
Replication
Explanation - Conjugation uses a sex pilus to transfer DNA plasmids.
Correct answer is: Conjugation
Q.118 Which bacterial species is a Gram-negative, rod-shaped organism that can produce a blue-green pigment in culture?
Pseudomonas aeruginosa
Staphylococcus aureus
Escherichia coli
Bacillus subtilis
Explanation - P. aeruginosa produces pyocyanin, giving a blue-green pigment.
Correct answer is: Pseudomonas aeruginosa
Q.119 Which bacterial genus is known for causing foodborne illnesses through toxin production?
Clostridium
Staphylococcus
Bacillus
All of the above
Explanation - All these genera can produce toxins causing foodborne disease.
Correct answer is: All of the above
Q.120 Which bacterial classification level is above genus and below phylum?
Family
Order
Class
Species
Explanation - Taxonomic hierarchy: Phylum > Class > Order > Family > Genus.
Correct answer is: Order
Q.121 Which bacterial genus is commonly used in the dairy industry to produce fermented products?
Lactobacillus
Staphylococcus
Pseudomonas
Bacillus
Explanation - Lactobacillus ferments lactose into lactic acid for cheese and yogurt.
Correct answer is: Lactobacillus
Q.122 Which bacterial genus is a common cause of dental caries due to acid production?
Streptococcus mutans
Staphylococcus aureus
Bacillus cereus
Pseudomonas aeruginosa
Explanation - S. mutans ferments sugar into acid, eroding enamel.
Correct answer is: Streptococcus mutans
Q.123 Which bacterial genus is a common cause of skin infections and abscesses?
Staphylococcus aureus
Escherichia coli
Pseudomonas aeruginosa
Salmonella enterica
Explanation - S. aureus infects skin, forming abscesses.
Correct answer is: Staphylococcus aureus
Q.124 Which bacterial genus is known for its ability to oxidize sulfur compounds in marine environments?
Thiobacillus
Streptococcus
E. coli
Bacillus
Explanation - Thiobacillus oxidizes sulfide to sulfate for energy.
Correct answer is: Thiobacillus
Q.125 Which bacterial species is a Gram-positive, spore-forming rod that causes anthrax?
Bacillus anthracis
Clostridium botulinum
Staphylococcus aureus
Escherichia coli
Explanation - B. anthracis forms spores and causes anthrax.
Correct answer is: Bacillus anthracis
Q.126 Which bacterial classification level includes organisms such as E. coli and Salmonella?
Enterobacteriaceae
Staphylococcaceae
Lactobacillaceae
Bacillaceae
Explanation - Enterobacteriaceae is a family of Gram-negative Enteric bacteria.
Correct answer is: Enterobacteriaceae
Q.127 Which bacterial genus is a common cause of urinary tract infections?
Escherichia coli
Staphylococcus aureus
Bacillus subtilis
Pseudomonas aeruginosa
Explanation - E. coli is the most frequent UTI pathogen.
Correct answer is: Escherichia coli
Q.128 Which bacterial genus is a common cause of pneumonia in children?
Streptococcus pneumoniae
Escherichia coli
Staphylococcus aureus
Pseudomonas aeruginosa
Explanation - S. pneumoniae causes most pediatric pneumonia cases.
Correct answer is: Streptococcus pneumoniae
Q.129 Which bacterial genus is a major cause of food poisoning due to toxin production?
Bacillus cereus
Staphylococcus aureus
Clostridium perfringens
All of the above
Explanation - All listed genera produce toxins leading to foodborne illness.
Correct answer is: All of the above
Q.130 Which bacterial process allows the exchange of plasmids between bacteria through a pilus?
Conjugation
Transformation
Transduction
Replication
Explanation - Conjugation uses a sex pilus to transfer DNA.
Correct answer is: Conjugation
Q.131 Which bacterial genus is known for producing lactic acid used in yogurt production?
Lactobacillus
Staphylococcus
Bacillus
Pseudomonas
Explanation - Lactobacillus ferments lactose to lactic acid.
Correct answer is: Lactobacillus
Q.132 Which bacterial classification level is above genus but below phylum?
Family
Order
Class
Species
Explanation - Taxonomic hierarchy: Phylum > Class > Order > Family > Genus.
Correct answer is: Order
Q.133 Which bacterial genus is a common cause of dental caries due to acid production?
Streptococcus mutans
Staphylococcus aureus
Bacillus cereus
Pseudomonas aeruginosa
Explanation - S. mutans ferments sugars to acid, damaging enamel.
Correct answer is: Streptococcus mutans
Q.134 Which bacterial genus is a common cause of skin infections and abscesses?
Staphylococcus aureus
Escherichia coli
Pseudomonas aeruginosa
Salmonella enterica
Explanation - S. aureus can invade skin, forming abscesses.
Correct answer is: Staphylococcus aureus
Q.135 Which bacterial genus is known for its ability to oxidize sulfur compounds in marine environments?
Thiobacillus
Streptococcus
E. coli
Bacillus
Explanation - Thiobacillus oxidizes sulfide to sulfate for energy.
Correct answer is: Thiobacillus
Q.136 Which bacterial species is a Gram-positive, spore-forming rod that causes anthrax?
Bacillus anthracis
Clostridium botulinum
Staphylococcus aureus
Escherichia coli
Explanation - B. anthracis forms spores and causes anthrax.
Correct answer is: Bacillus anthracis
Q.137 Which bacterial classification level includes organisms such as E. coli and Salmonella?
Enterobacteriaceae
Staphylococcaceae
Lactobacillaceae
Bacillaceae
Explanation - Enterobacteriaceae is a family of Gram-negative Enteric bacteria.
Correct answer is: Enterobacteriaceae
Q.138 Which bacterial genus is a common cause of urinary tract infections?
Escherichia coli
Staphylococcus aureus
Bacillus subtilis
Pseudomonas aeruginosa
Explanation - E. coli is the most frequent UTI pathogen.
Correct answer is: Escherichia coli
Q.139 Which bacterial genus is a major cause of pneumonia in children?
Streptococcus pneumoniae
Escherichia coli
Staphylococcus aureus
Pseudomonas aeruginosa
Explanation - S. pneumoniae causes most pediatric pneumonia cases.
Correct answer is: Streptococcus pneumoniae
Q.140 Which bacterial genus is a major cause of food poisoning due to toxin production?
Bacillus cereus
Staphylococcus aureus
Clostridium perfringens
All of the above
Explanation - All listed genera produce toxins leading to foodborne illness.
Correct answer is: All of the above
Q.141 Which bacterial process allows the exchange of plasmids between bacteria through a pilus?
Conjugation
Transformation
Transduction
Replication
Explanation - Conjugation uses a sex pilus to transfer DNA.
Correct answer is: Conjugation
Q.142 Which bacterial genus is known for producing lactic acid used in yogurt production?
Lactobacillus
Staphylococcus
Bacillus
Pseudomonas
Explanation - Lactobacillus ferments lactose to lactic acid.
Correct answer is: Lactobacillus
Q.143 Which bacterial classification level is above genus but below phylum?
Family
Order
Class
Species
Explanation - Taxonomic hierarchy: Phylum > Class > Order > Family > Genus.
Correct answer is: Order