Introduction to microbiology MCQs With Answer

Introduction to microbiology MCQs With Answer

Microbiology is a core subject for B.Pharm students, covering bacteria, viruses, fungi, sterilization, aseptic techniques, antimicrobial mechanisms and laboratory diagnostics. This Introduction to microbiology MCQs With Answer provides concise, exam-focused questions that reinforce concepts such as Gram staining, culture media, sterilization parameters, antibiotic resistance, endotoxins and molecular methods like PCR. Each MCQ emphasizes pharmaceutical relevance—bioburden control, sterility assurance, preservative testing and infection control—helping students link theory to practical quality-control and clinical applications. Practice these targeted questions to build critical thinking and improve performance in university exams and professional pharmacy assessments. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary focus of microbiology as a scientific discipline?

• The study of chemical reactions in drugs
• The study of microorganisms and their interactions
• The engineering of pharmaceutical equipment
• The analysis of human genetics

Correct Answer: The study of microorganisms and their interactions

Q2. In Gram staining, what is the key structural feature that causes bacteria to appear purple (Gram-positive)?

• Thin outer membrane rich in lipopolysaccharide
• Presence of a thick peptidoglycan layer
• High content of teichoic acid in the outer membrane
• Presence of a capsule made of polysaccharides

Correct Answer: Presence of a thick peptidoglycan layer

Q3. Which of the following organisms is Gram-negative and typically appears pink/red after Gram staining?

• Staphylococcus aureus
• Escherichia coli
• Bacillus subtilis
• Streptococcus pneumoniae

Correct Answer: Escherichia coli

Q4. Which bacterial structure confers high resistance to heat, desiccation and chemicals?

• Pili
• Endospore
• Capsule
• Flagellum

Correct Answer: Endospore

Q5. What are standard autoclave conditions commonly used for steam sterilization of laboratory media?

• 100°C for 60 minutes
• 121°C, 15 psi for 15 minutes
• 160°C for 2 hours
• 37°C for 24 hours

Correct Answer: 121°C, 15 psi for 15 minutes

Q6. Which membrane filter pore size is typically used to sterilize solutions by removing bacteria?

• 5.0 µm
• 0.45 µm
• 0.22 µm
• 1.2 µm

Correct Answer: 0.22 µm

Q7. The Limulus amebocyte lysate (LAL) test is primarily used to detect which contaminant in pharmaceuticals?

• Mycotoxins
• Endotoxins (lipopolysaccharide)
• Viral particles
• Bacterial spores

Correct Answer: Endotoxins (lipopolysaccharide)

Q8. What does Minimum Inhibitory Concentration (MIC) represent in antimicrobial testing?

• The maximum drug concentration that is safe for patients
• The lowest concentration that prevents visible bacterial growth
• The concentration that kills 99.999% of bacteria
• The concentration required to inhibit viral replication

Correct Answer: The lowest concentration that prevents visible bacterial growth

Q9. What does Minimum Bactericidal Concentration (MBC) measure?

• Lowest concentration that kills a defined percentage of bacteria
• Minimum concentration inhibiting viral enzymes
• Maximum tolerated antibiotic dose in humans
• The time required to reduce bacterial count by 90%

Correct Answer: Lowest concentration that kills a defined percentage of bacteria

Q10. Which term best describes an antibiotic that inhibits bacterial growth without directly killing the organism?

• Bactericidal
• Bacteriostatic
• Virucidal
• Sporicidal

Correct Answer: Bacteriostatic

Q11. Beta-lactam antibiotics like penicillin primarily inhibit which bacterial target?

• 50S ribosomal subunit
• Cell wall synthesis (peptidoglycan cross-linking)
• DNA gyrase
• Folic acid synthesis

Correct Answer: Cell wall synthesis (peptidoglycan cross-linking)

Q12. Aminoglycosides primarily affect which process in bacteria?

• Inhibit cell wall synthesis
• Inhibit 30S ribosomal subunit causing misreading
• Block folate metabolism
• Disrupt cell membrane ergosterol

Correct Answer: Inhibit 30S ribosomal subunit causing misreading

Q13. Macrolide antibiotics like erythromycin act by binding to which bacterial component?

• DNA polymerase
• 30S ribosomal subunit
• 50S ribosomal subunit
• Cell membrane lipids

Correct Answer: 50S ribosomal subunit

Q14. Which genetic element is commonly responsible for horizontal transfer of antibiotic resistance genes between bacteria?

• Mitochondrial DNA
• Plasmids
• Ribosomal RNA
• Capsular polysaccharide

Correct Answer: Plasmids

Q15. Which mechanism of gene transfer involves bacteriophages carrying bacterial DNA between cells?

• Conjugation
• Transformation
• Transduction
• Binary fission

Correct Answer: Transduction

Q16. Which culture medium is selective for Gram-negative enteric bacteria and differentiates lactose fermenters?

• Blood agar
• MacConkey agar
• Sabouraud dextrose agar
• Mannitol salt agar

Correct Answer: MacConkey agar

Q17. Which staining method is used to identify Mycobacterium species due to their mycolic acid-rich cell walls?

• Gram stain
• Acid-fast (Ziehl–Neelsen) stain
• India ink stain
• Endospore stain

Correct Answer: Acid-fast (Ziehl–Neelsen) stain

Q18. What is the correct sequence of bacterial growth phases in a closed system?

• Log, lag, stationary, death
• Lag, log, stationary, death
• Stationary, log, lag, death
• Log, stationary, lag, death

Correct Answer: Lag, log, stationary, death

Q19. Generation time in microbiology refers to which of the following?

• Time for a single cell to form a spore
• Time required for a microbial population to double
• Time for antibiotic to kill bacteria
• Time to sterilize a product in autoclave

Correct Answer: Time required for a microbial population to double

Q20. Obligate anaerobic bacteria are characterized by which property?

• They require oxygen for growth
• They are killed or inhibited by oxygen
• They only grow at high salt concentrations
• They require light for metabolism

Correct Answer: They are killed or inhibited by oxygen

Q21. The catalase test differentiates which two genera commonly found in clinical microbiology?

• Escherichia and Salmonella
• Staphylococcus (catalase positive) and Streptococcus (catalase negative)
• Bacillus and Clostridium
• Mycobacterium and Nocardia

Correct Answer: Staphylococcus (catalase positive) and Streptococcus (catalase negative)

Q22. Coagulase positivity is a key diagnostic trait of which species?

• Staphylococcus aureus
• Staphylococcus epidermidis
• Streptococcus pyogenes
• Enterococcus faecalis

Correct Answer: Staphylococcus aureus

Q23. Beta-lactamase enzymes produced by bacteria have what primary effect?

• Enhance cell membrane permeability
• Hydrolyze beta-lactam antibiotics rendering them ineffective
• Increase peptidoglycan synthesis
• Inhibit 30S ribosomal subunit

Correct Answer: Hydrolyze beta-lactam antibiotics rendering them ineffective

Q24. Endotoxin is a potent pyrogen originating from which bacterial structure?

• Teichoic acids of Gram-positive cell wall
• Outer membrane lipopolysaccharide (LPS) of Gram-negative bacteria
• Exotoxin secretion system
• Capsular polysaccharide layer

Correct Answer: Outer membrane lipopolysaccharide (LPS) of Gram-negative bacteria

Q25. Exotoxins differ from endotoxins in that exotoxins are typically:

• Integral cell wall components released on cell death
• Heat-stable lipopolysaccharides
• Protein secreted by bacteria that often have specific enzymatic activities
• Only produced by Gram-negative bacteria

Correct Answer: Protein secreted by bacteria that often have specific enzymatic activities

Q26. Which genera are well-known spore-forming bacteria relevant to pharmaceutical contamination?

• Bacillus and Clostridium
• Staphylococcus and Streptococcus
• Escherichia and Salmonella
• Pseudomonas and Acinetobacter

Correct Answer: Bacillus and Clostridium

Q27. Which method is commonly used to determine total viable count or bioburden in pharmaceutical samples?

• Gram staining
• Plate count (colony forming units, CFU) on appropriate agar
• Direct microscopy without culture
• ELISA for toxins

Correct Answer: Plate count (colony forming units, CFU) on appropriate agar

Q28. Which disinfectant is widely used as an effective sporicidal agent when used at appropriate concentrations?

• 70% ethanol
• Sodium hypochlorite (bleach)
• Soap and water
• Neutral pH detergents

Correct Answer: Sodium hypochlorite (bleach)

Q29. HEPA filters used in sterile manufacturing are certified to remove particles down to which size with high efficiency?

• 5.0 µm at 90% efficiency
• 0.3 µm at 99.97% efficiency
• 10 µm at 50% efficiency
• 1.0 µm at 75% efficiency

Correct Answer: 0.3 µm at 99.97% efficiency

Q30. PCR (polymerase chain reaction) is a molecular technique primarily used to amplify which molecule?

• Proteins
• DNA
• Lipids
• Polysaccharides

Correct Answer: DNA

Q31. Reverse transcription PCR (RT-PCR) is specifically used to detect which type of genetic material?

• Genomic DNA only
• RNA (after conversion to cDNA)
• Protein sequences
• Lipid A components

Correct Answer: RNA (after conversion to cDNA)

Q32. In bacteriophage biology, which cycle leads to immediate lysis of the host cell and release of progeny phages?

• Lysogenic cycle
• Lytic cycle
• Symbiotic cycle
• Conjugative cycle

Correct Answer: Lytic cycle

Q33. Viruses are best described as which of the following?

• Cells with organelles and metabolic activity
• Non-cellular particles composed of nucleic acid enclosed in a protein coat
• Autonomous bacteria that replicate by binary fission
• Fungal spores requiring sunlight

Correct Answer: Non-cellular particles composed of nucleic acid enclosed in a protein coat

Q34. Candida albicans is classified as which type of microorganism commonly relevant to pharmacy students?

• Gram-negative bacillus
• Yeast (fungus)
• Mycobacterium species
• Protozoan parasite

Correct Answer: Yeast (fungus)

Q35. Antimicrobial stewardship programs primarily aim to achieve which outcome?

• Increase indiscriminate antibiotic use
• Reduce antimicrobial resistance and optimize therapy
• Eliminate all bacterial flora in hospitals
• Promote over-the-counter antibiotic sales

Correct Answer: Reduce antimicrobial resistance and optimize therapy

Q36. Tetracyclines exert their antibacterial effect by targeting which component?

• Cell wall transpeptidase
• 30S ribosomal subunit, blocking tRNA binding
• DNA gyrase exclusively
• Fungal ergosterol synthesis

Correct Answer: 30S ribosomal subunit, blocking tRNA binding

Q37. Azole antifungal drugs primarily inhibit which biosynthetic pathway in fungi?

• Cellulose synthesis
• Ergosterol synthesis in fungal cell membranes
• Peptidoglycan cross-linking
• RNA polymerase activity

Correct Answer: Ergosterol synthesis in fungal cell membranes

Q38. Dipicolinic acid is associated with which microbial structure and contributes to its stability?

• Capsule
• Endospore
• Pilus
• Outer membrane vesicle

Correct Answer: Endospore

Q39. In sterilization science, the D-value refers to which parameter?

• Temperature required to kill all microbes
• Time required at a given temperature to reduce the microbial population by 90%
• pH value at which disinfectant is active
• Concentration of disinfectant needed for sporicidal action

Correct Answer: Time required at a given temperature to reduce the microbial population by 90%

Q40. The Z-value in thermal inactivation studies is defined as:

• The change in temperature required to change the D-value by one log (tenfold)
• The number of spores surviving after sterilization
• The pH range for enzyme activity
• The time to achieve sterility assurance level

Correct Answer: The change in temperature required to change the D-value by one log (tenfold)

Q41. Bioburden in pharmaceutical context refers to:

• Total number of chemical impurities
• Number of viable microorganisms on or in a product prior to sterilization
• Level of heavy metal contamination
• Amount of endotoxin only

Correct Answer: Number of viable microorganisms on or in a product prior to sterilization

Q42. Sterility assurance level (SAL) commonly accepted for terminally sterilized pharmaceuticals is:

• 10^0
• 10^-3
• 10^-6
• 1% survival rate

Correct Answer: 10^-6

Q43. Which biosafety level (BSL) is appropriate for work with airborne pathogens like Mycobacterium tuberculosis?

• BSL-1
• BSL-2
• BSL-3
• BSL-4

Correct Answer: BSL-3

Q44. Lactic acid bacteria such as Lactobacillus are primarily known for which metabolic activity?

• Oxidative phosphorylation exclusively
• Production of lactic acid by fermentation
• Synthesis of lipopolysaccharide
• Spore formation

Correct Answer: Production of lactic acid by fermentation

Q45. In aseptic processing of parenteral products, which environment is typically used to provide an ISO 5 (class 100) critical area?

• Ordinary room air
• Laminar airflow hood or isolator with HEPA filtration
• Open bench without filtration
• Non-ventilated cabinet

Correct Answer: Laminar airflow hood or isolator with HEPA filtration

Q46. The rabbit pyrogen test historically detects which property of injectable products?

• Antibiotic potency
• Presence of pyrogens (fever-inducing substances)
• Sterility against fungi
• Endotoxin concentration by modern standards

Correct Answer: Presence of pyrogens (fever-inducing substances)

Q47. Which microbial structure primarily helps bacteria evade phagocytosis by host immune cells?

• Flagella
• Capsule
• Pili
• Ribosomes

Correct Answer: Capsule

Q48. Which test is a standard phenotypic method for assessing antibiotic susceptibility using zones of inhibition on agar?

• ELISA
• Kirby–Bauer disk diffusion test
• Western blot
• Gram staining

Correct Answer: Kirby–Bauer disk diffusion test

Q49. Which biochemical test distinguishes lactose fermenters on MacConkey agar by producing pink colonies?

• Oxidase test
• Lactose fermentation with acid production
• Coagulase production
• Urease activity turning medium pink

Correct Answer: Lactose fermentation with acid production

Q50. Which mechanism is a common cause of bacterial resistance to aminoglycosides?

• Alteration of cell wall peptidoglycan
• Enzymatic modification (acetylation/phosphorylation) of the drug
• Increased ergosterol synthesis
• Overexpression of DNA gyrase

Correct Answer: Enzymatic modification (acetylation/phosphorylation) of the drug

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com