Introduction
These 50+ microbiology interview questions and answers for fresher’s cover everything from basics to lab techniques and current trends, helping you confidently clear interviews for roles in quality control, food, pharmaceutical, clinical, and environmental microbiology.
Basic Microbiology Interview Questions
Q1. What is microbiology?
Microbiology is the branch of science that studies microscopic organisms such as bacteria, viruses, fungi, protozoa, and algae — including their physiology, genetics, structure, and roles in the environment, industry, and disease.
Q2. Who is known as the father of microbiology?
Anton van Leeuwenhoek is known as the father of microbiology because he was the first to observe and describe microorganisms using a simple microscope.
Q3. What are the main branches of microbiology?
- Bacteriology – study of bacteria
- Virology – study of viruses
- Mycology – study of fungi
- Parasitology – study of parasites
- Immunology – study of immune system
- Phycology – study of algae
- Microbial genetics and biotechnology
Q4. What is the difference between prokaryotic and eukaryotic cells?
| Feature | Prokaryotic Cell | Eukaryotic Cell |
| Nucleus | Absent | Present |
| Cell size | Small (1–10 µm) | Large (10–100 µm) |
Organelles | No membrane-bound organelles | Membrane-bound organelles present |
| Example | Bacteria | Fungi, Protozoa, Algae |
Q5. What is a culture medium?
A culture medium is a nutrient-rich environment used for growing microorganisms in the laboratory. It can be solid (agar) or liquid (broth).
Q6. What is the difference between selective and differential media?
- Selective media allow growth of specific microorganisms while inhibiting others (e.g., MacConkey agar).
- Differential media distinguish between microorganisms based on biochemical reactions (e.g., Blood agar).
Q7. What are Koch’s postulates?
Koch’s postulates are four criteria used to establish a causal relationship between a microorganism and a disease:
- The microorganism must be found in all cases of the disease.
- It must be isolated and grown in pure culture.
- The cultured organism should cause disease when introduced into a healthy host.
- The same organism must be re-isolated from the newly infected host.
Laboratory Techniques Interview Questions
Q8. What is aseptic technique?
Aseptic technique involves procedures that prevent contamination of cultures and sterile media by unwanted microorganisms. It includes flame sterilization, hand hygiene, and working near a flame.
Q9. What is Gram staining?
Gram staining is a differential staining method used to classify bacteria into Gram-positive (purple) and Gram-negative (pink/red) based on their cell wall structure.
Q10. What is the purpose of autoclaving?
Autoclaving sterilizes materials using steam under pressure (121°C, 15 psi for 15–20 minutes) to kill all microorganisms, including spores.
Q11. What is the difference between sterilization and disinfection?
- Sterilization: Kills all microorganisms including spores.
- Disinfection: Reduces or eliminates most pathogenic microorganisms, but not necessarily spores.
Q12. What is a pure culture?
A pure culture contains only one type of microorganism, obtained through streak plate or pour plate methods.
Q13. What is the role of agar in culture media?
Agar acts as a solidifying agent for culture media. It is not metabolized by most microorganisms.
Applied Microbiology Interview Questions
Q14. What is fermentation?
Fermentation is the anaerobic breakdown of carbohydrates by microorganisms to produce energy, along with by-products such as alcohol, lactic acid, or gases.
Q15. Name some industrial products produced by microorganisms.
- Antibiotics (Penicillin)
- Enzymes (Amylase, Protease)
- Vitamins (B12, Riboflavin)
- Beverages (Beer, Wine)
- Organic acids (Citric acid, Lactic acid)
Q16. What are probiotics?
Probiotics are live beneficial microorganisms that, when consumed in adequate amounts, promote gut health and improve digestion and immunity.
Q17. What is the role of microbiology in medicine?
Microbiology helps identify pathogens, understand disease mechanisms, develop vaccines, antibiotics, and improve diagnostic tools.
Environmental & Food Microbiology Interview Questions
Q18. What is nitrogen fixation?
It is the process by which certain bacteria (e.g., Rhizobium, Azotobacter) convert atmospheric nitrogen (N₂) into ammonia (NH₃), making it available to plants.
Q19. How does microbiology help in wastewater treatment?
Microorganisms degrade organic matter in sewage, reducing pollution and producing useful by-products like biogas.
Q20. What are foodborne pathogens?
Microbes that cause food poisoning or infection, such as Salmonella, E. coli, Listeria monocytogenes, and Clostridium botulinum.
Recent & General Awareness Interview Questions
Q21. What is antimicrobial resistance (AMR)?
AMR occurs when microorganisms evolve mechanisms to survive exposure to antibiotics or other antimicrobial agents, making infections harder to treat.
Q22. What are vaccines and how do they work?
Vaccines stimulate the immune system to recognize and fight specific pathogens by exposing the body to harmless forms or parts of the microorganism (antigens).
Q23. What are biosafety levels (BSL)?
Laboratories are classified from BSL-1 to BSL-4 based on the risk level of pathogens handled, with BSL-4 being the highest containment.
Q24. What are endospores?
Endospores are highly resistant, dormant structures formed by certain bacteria (e.g., Bacillus, Clostridium) to survive extreme conditions.
Q25. What is the difference between aerobic and anaerobic bacteria?
- Aerobic bacteria require oxygen for growth.
- Anaerobic bacteria grow in the absence of oxygen.
Advanced Microbiology Interview Questions
Q26. What is the difference between infection and disease?
- Infection: Occurs when microorganisms invade and multiply in the host.
- Disease: Occurs when infection causes damage to tissues or impairs normal body functions.
Q27. What are pathogens?
Pathogens are microorganisms (bacteria, viruses, fungi, protozoa, or prions) that cause diseases in humans, animals, or plants.
Q28. What is normal flora?
Normal flora refers to the collection of microorganisms that normally live on or inside the human body without causing disease. They help in protection and nutrient synthesis.
Q29. What are antibiotics? Give examples.
Antibiotics are chemical substances produced by microorganisms that kill or inhibit the growth of other microbes.
Examples: Penicillin, Streptomycin, Tetracycline, Erythromycin.
Q30. What are the modes of transmission of infectious diseases
- Direct contact (touching, kissing)
- Airborne (sneezing, coughing)
- Vector-borne (mosquitoes, flies)
- Food and water-borne
- Fomites (contaminated objects)
Q31. What is the difference between endotoxin and exotoxin?
| Feature | Exotoxin | Endotoxin |
| Origin | Secreted by living bacteria | Part of cell wall of Gram-negative bacteria |
| Heat stability | Heat labile | Heat stable |
| Toxicity | Highly toxic | Less toxic |
| Example | Tetanus toxin | Lipopolysaccharide (LPS) |
Q32. What is microbial growth curve?
It represents the growth of bacteria in a closed system over time, consisting of four phases:
- Lag phase
- Log (Exponential) phase
- Stationary phase
- Death phase
Q33. What are plasmids?
Plasmids are small, circular, double-stranded DNA molecules separate from chromosomal DNA that often carry antibiotic resistance or virulence genes.
Q34. What is transformation in bacteria?
Transformation is the process by which a bacterium takes up free DNA from its environment and incorporates it into its genome.
Q35. What are bacteriophages?
Bacteriophages (or phages) are viruses that infect and replicate within bacteria.
Q36. What is PCR (Polymerase Chain Reaction)?
PCR is a molecular biology technique used to amplify specific DNA sequences using primers, DNA polymerase, and repeated cycles of heating and cooling.
Q37. What is the principle of ELISA?
The Enzyme-Linked Immunosorbent Assay (ELISA) detects antigens or antibodies using enzyme-substrate color reactions for diagnostic purposes.
Q38. What is the purpose of streak plate method?
The streak plate method isolates pure colonies of bacteria from a mixed sample by spreading the inoculum over an agar surface.
Q39. What is microbial contamination?
It refers to the unwanted presence of microorganisms in sterile materials, cultures, or environments, often leading to experimental or product failure.
Q40. What are halophiles, thermophiles, and psychrophiles?
- Halophiles: Grow in high salt concentrations.
- Thermophiles: Thrive at high temperatures (above 45°C).
- Psychrophiles: Grow at low temperatures (below 15°C).
Q41. What is the use of a spectrophotometer in microbiology?
It measures the optical density (OD) of microbial cultures to estimate cell concentration or growth rate.
Q42. What is the function of a biosafety cabinet?
A biosafety cabinet provides a sterile, contained workspace for handling infectious materials safely, using HEPA-filtered airflow.
Q43. What are anaerobic jars or chambers used for?
They provide oxygen-free environments to culture anaerobic microorganisms.
Q44. What is a biofilm?
A biofilm is a community of microorganisms that adhere to surfaces and are enclosed in a self-produced matrix of extracellular polymeric substances.
Q45. What is the difference between lytic and lysogenic cycles?
- Lytic cycle: The phage replicates rapidly and lyses the host cell.
- Lysogenic cycle: The phage DNA integrates into the host genome and replicates silently before activation.
Q46. What is zoonosis?
Zoonosis is a disease that can be transmitted from animals to humans, such as rabies or avian influenza.
Q47. What are mycorrhizae?
Mycorrhizae are symbiotic associations between fungi and plant roots that help in nutrient and water absorption.
Q48. What are extremophiles?
Microorganisms that live in extreme conditions such as high temperature, pressure, acidity, or salinity (e.g., Thermus aquaticus).
Q49. What is quorum sensing?
It is a communication mechanism among bacteria through chemical signals to coordinate gene expression based on cell population density.
Q50. What is the role of microbiology in biotechnology?
Microbiology supports biotechnology through:
- Production of recombinant proteins
- Vaccine development
- Genetic engineering
- Bioremediation
- Industrial enzyme production
Practical/Instrument-Based Interview Questions
Q51. What is the purpose of a hemocytometer?
It is a counting chamber used to estimate cell concentration in liquid samples, including microbial or blood cell suspensions.
Q52. What are the common staining techniques in microbiology?
- Gram staining
- Acid-fast staining
- Endospore staining
- Capsule staining
- Negative staining
Q53. What is the use of a centrifuge in microbiology?
A centrifuge separates components of mixtures (cells, spores, proteins) based on density using rapid spinning.
Q54. What is turbidity in microbiology?
Turbidity refers to the cloudiness of a microbial suspension, indicating bacterial growth in a liquid medium.
Q55. What is the difference between transient and resident microflora?
- Resident flora: Permanently present on the body.
- Transient flora: Temporarily present and easily removed by washing.
Q56. What is the difference between contamination and infection?
- Contamination: Unwanted introduction of microbes into sterile environments.
- Infection: Invasion and multiplication of microbes inside the host body.
Q57. What is microbial taxonomy?
Microbial taxonomy is the classification, naming, and identification of microorganisms based on genetic, biochemical, and morphological characteristics.
Q58. What is a spore stain?
A differential stain used to detect bacterial endospores (e.g., Schaeffer-Fulton method).
Q59. What is the function of buffers in media preparation?
Buffers maintain a stable pH in the culture medium during microbial growth.
Q60. What is a colony-forming unit (CFU)?
A CFU represents a single microorganism or a group of cells that multiply to form one visible colony on an agar plate.
Tips for Microbiology Interview Preparation
- Revise basic laboratory techniques and instruments (microscope, autoclave, laminar flow).
- Understand microbial classification and staining techniques.
- Be ready to explain one or two practical experiments you performed.
- Keep updated on recent advances like CRISPR, antimicrobial resistance, and COVID-19 virology.
Conclusion
Microbiology interviews for freshers focus on fundamental concepts, practical lab knowledge, and basic applications. Review these questions to confidently face interviews for positions like Microbiology Lab Assistant, QC Analyst, or Research Intern.
Reference and Sources
