Types of microbial spoilage MCQs With Answer

Introduction: Understanding the “Types of microbial spoilage MCQs With Answer” is essential for B. Pharm students preparing for exams and practical pharmacy work. This focused guide covers microbial spoilage mechanisms, common spoilage organisms (bacteria, yeasts, molds), product vulnerabilities, detection methods, preservative selection, and control strategies relevant to pharmaceutical products. Clear keyword coverage—microbial spoilage, types of microbial spoilage, preservatives, bioburden, sterility testing, and pharmaceutical contamination—helps both learning and SEO. Each question emphasizes real-world pharmaceutics implications, testable facts, and preservative compatibility. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary distinction between bacterial spoilage and fungal spoilage in pharmaceutical liquids?

• Bacterial spoilage usually causes visible particulate formation while fungal spoilage never does
• Bacterial spoilage typically leads to turbidity and gas production; fungal spoilage often produces filamentous growth and mycelia
• Fungal spoilage only occurs in solid dosage forms
• Bacterial spoilage only occurs at temperatures below refrigeration

Correct Answer: Bacterial spoilage typically leads to turbidity and gas production; fungal spoilage often produces filamentous growth and mycelia

Q2. Which organism is most commonly associated with aqueous pharmaceutical product spoilage due to its ability to grow in low-nutrient environments?

• Aspergillus niger
• Pseudomonas aeruginosa
• Saccharomyces cerevisiae
• Bacillus subtilis

Correct Answer: Pseudomonas aeruginosa

Q3. Which spoilage mechanism involves cleavage of ester bonds in prodrugs or excipients leading to loss of potency?

• Oxidation
• Hydrolysis
• Fermentation
• Denaturation

Correct Answer: Hydrolysis

Q4. Water activity (aw) below which most bacteria cannot grow, but some molds and yeasts can?

• aw 0.90
• aw 0.85
• aw 0.70
• aw 0.60

Correct Answer: aw 0.70

Q5. Which preservative is commonly used in acidic oral syrups because of its activity at low pH?

• Phenol
• Benzoic acid (sodium benzoate)
• Chlorhexidine
• Formaldehyde

Correct Answer: Benzoic acid (sodium benzoate)

Q6. The preservative efficacy (challenge) test primarily evaluates:

• The chemical stability of preservatives over time
• The in vitro antimicrobial activity of the preservative against specified challenge organisms in the product
• The acute toxicity of preservatives in humans
• The ability of preservatives to act as antioxidants

Correct Answer: The in vitro antimicrobial activity of the preservative against specified challenge organisms in the product

Q7. Which of the following is a common indicator organism for inadequate sterilization in parenteral manufacturing?

• Staphylococcus epidermidis
• Geobacillus stearothermophilus
• Pseudomonas putida
• Saccharomyces boulardii

Correct Answer: Geobacillus stearothermophilus

Q8. Endotoxins are primarily associated with which group of organisms?

• Gram-positive bacteria
• Gram-negative bacteria
• Fungi
• Viruses

Correct Answer: Gram-negative bacteria

Q9. Which spoilage sign is most indicative of fungal contamination in creams and ointments?

• Gas production and explosion of the container
• Surface powdery growth, pigmentation or fuzzy colonies
• Complete dissolution of the semisolid base
• Loss of emulsion viscosity only

Correct Answer: Surface powdery growth, pigmentation or fuzzy colonies

Q10. Which parameter most strongly affects preservative activity and must be considered during formulation?

• Color of the container
• pH of the formulation
• Molar mass of the active pharmaceutical ingredient
• Time of day of manufacturing

Correct Answer: pH of the formulation

Q11. Which type of microorganism is most resistant to common disinfectants and is a frequent contaminant in dry pharmaceutical powders?

• Gram-negative rods
• Yeasts
• Spore-forming bacilli (Bacillus spp.)
• Enveloped viruses

Correct Answer: Spore-forming bacilli (Bacillus spp.)

Q12. In preserved multi-dose parenteral formulations, which factor can reduce preservative efficacy the most?

• High packaging integrity
• Frequent inoculation via the needleless access causing dilution and neutralization
• Low storage temperature
• Use of amber glass vials

Correct Answer: Frequent inoculation via the needleless access causing dilution and neutralization

Q13. The USP microbial limit test for non-sterile products assesses:

• Only the presence of endotoxin
• Total aerobic microbial count and specified objectionable organisms
• Sterility of the product
• Viscosity changes due to microbial enzymes

Correct Answer: Total aerobic microbial count and specified objectionable organisms

Q14. Which chemical reaction by microbes commonly causes rancidity in lipid-containing topical formulations?

• Proteolysis
• Lipolysis by lipases
• Carbohydrate fermentation
• Nitrification

Correct Answer: Lipolysis by lipases

Q15. Which method is most appropriate to detect viable but non-culturable (VBNC) bacteria in a contaminated product?

• Standard plate count only
• ATP bioluminescence or molecular methods (PCR/flow cytometry)
• Visual inspection
• pH measurement

Correct Answer: ATP bioluminescence or molecular methods (PCR/flow cytometry)

Q16. Which preservative is typically avoided in ophthalmic products due to irritation and toxicity concerns?

• Benzalkonium chloride at high concentrations
• Sodium benzoate
• Parabens at low concentration
• Potassium sorbate

Correct Answer: Benzalkonium chloride at high concentrations

Q17. Which microbial spoilage type involves conversion of sugars to acids, alcohols, or gases, altering drug taste and pH?

• Oxidative spoilage
• Fermentative spoilage
• Proteolytic spoilage
• Radiolytic spoilage

Correct Answer: Fermentative spoilage

Q18. What is the major reason why solids like tablets are less susceptible to microbial spoilage than liquids?

• Solids always contain preservatives
• Lower water activity and less accessible nutrients
• Tablets are always sterilized
• Microbes cannot adhere to solid surfaces

Correct Answer: Lower water activity and less accessible nutrients

Q19. Which biochemical product from molds is of particular concern because it can contaminate raw materials and finished products with toxic effects?

• Exotoxins
• Endotoxins
• Mycotoxins (e.g., aflatoxins)
• Capsular polysaccharides

Correct Answer: Mycotoxins (e.g., aflatoxins)

Q20. Autoclaving at 121°C for 15 minutes is designed to inactivate which microbial form most resistant to moist heat?

• Vegetative Gram-negative bacteria
• Fungal spores
• Endospores of thermophilic spore formers
• Enveloped viruses

Correct Answer: Endospores of thermophilic spore formers

Q21. The presence of a musty odor in a stored herbal extract most likely indicates spoilage by:

• Gram-positive cocci
• Yeasts
• Molds producing volatile secondary metabolites
• Algal contamination

Correct Answer: Molds producing volatile secondary metabolites

Q22. Which excipient property can promote microbial growth if not properly controlled?

• Hydrophobicity and low solubility
• High water content or hygroscopic nature
• High melting point
• Low molecular weight

Correct Answer: High water content or hygroscopic nature

Q23. Which organism listed is a common yeast contaminant in pharmaceutical oral liquids?

• Clostridium perfringens
• Saccharomyces cerevisiae
• Streptococcus pyogenes
• Geotrichum candidum

Correct Answer: Saccharomyces cerevisiae

Q24. Which analytical test specifically quantifies endotoxin contamination in injectable products?

• Microbial limit test
• LAL (Limulus Amebocyte Lysate) test
• Preservative efficacy test
• Aerobic plate count

Correct Answer: LAL (Limulus Amebocyte Lysate) test

Q25. What is a common outcome when antioxidants are used incorrectly in formulations in relation to microbial spoilage?

• They directly kill microbes
• They always increase preservative efficacy
• They may interact with preservatives and reduce antimicrobial effectiveness
• They change water activity

Correct Answer: They may interact with preservatives and reduce antimicrobial effectiveness

Q26. Which growth phase of microbes is most vulnerable to antimicrobial agents during challenge tests?

• Lag phase
• Exponential (log) phase
• Stationary phase
• Death phase

Correct Answer: Exponential (log) phase

Q27. Which of the following is an objectionable organism in non-sterile pharmaceutical products due to potential pathogenicity?

• Bacillus subtilis
• Escherichia coli
• Micrococcus luteus
• Penicillium chrysogenum

Correct Answer: Escherichia coli

Q28. Which factor is LEAST likely to promote microbial spoilage in an oil-in-water emulsion?

• High continuous aqueous phase
• Use of non-ionic emulsifiers with limited antimicrobial effect
• Presence of sugars as nutrients
• High oil content with minimal aqueous phase

Correct Answer: High oil content with minimal aqueous phase

Q29. The term ‘bioburden’ in pharmaceutical manufacturing refers to:

• Total count of viable microorganisms on a product or surface before sterilization
• Non-viable particle count in cleanrooms
• Concentration of active drug per unit mass
• Amount of endotoxin present

Correct Answer: Total count of viable microorganisms on a product or surface before sterilization

Q30. Which practice reduces the risk of preservative neutralization in multi-dose containers?

• Frequent opening and topping up with non-sterile water
• Using latex stoppers that may adsorb preservatives
• Designing preservative concentration and formulation to resist dilution and neutralization
• Storing at fluctuating high temperatures

Correct Answer: Designing preservative concentration and formulation to resist dilution and neutralization

Q31. Which organism is commonly used as a bacterial challenge strain for preservative efficacy tests due to its preservative tolerance?

• Lactobacillus acidophilus
• Pseudomonas aeruginosa
• Bifidobacterium longum
• Rhizopus oryzae

Correct Answer: Pseudomonas aeruginosa

Q32. Hydrogen peroxide residues in packaging are most likely to cause what type of spoilage-related issue if not removed?

• Microbial proliferation due to nutrient effects
• Chemical oxidation of sensitive APIs
• Increase in water activity
• Enhanced preservative efficacy

Correct Answer: Chemical oxidation of sensitive APIs

Q33. Which environmental control is most critical in preventing airborne fungal contamination in a pharmaceutical manufacturing area?

• Relative humidity and HEPA filtration
• Lighting intensity
• Floor color
• Availability of hand soap

Correct Answer: Relative humidity and HEPA filtration

Q34. Which microbial enzyme commonly produced by bacteria leads to the breakdown of protein-based gel matrices in topical products?

• Lipase
• Protease
• Amylase
• Cellulase

Correct Answer: Protease

Q35. Which storage condition would most likely accelerate microbial spoilage of an aqueous oral solution?

• Refrigeration at 4°C
• Stored at 25°C in sealed amber bottles
• Exposure to fluctuating high temperatures and contamination
• Storage under nitrogen atmosphere

Correct Answer: Exposure to fluctuating high temperatures and contamination

Q36. Which statement best describes ‘objectionable organisms’ in the context of pharmaceutical microbial testing?

• Organisms that change the color of a formulation only
• Microbes that are potentially pathogenic or indicative of poor hygiene and must be absent
• Non-viable particles detected by cascade impactors
• Organisms used in probiotic formulations

Correct Answer: Microbes that are potentially pathogenic or indicative of poor hygiene and must be absent

Q37. In pharmaceutical liquids, which preservative group acts by disrupting microbial cell membranes?

• Alcohols and quaternary ammonium compounds
• Reducing sugars
• Chelating agents only
• Non-ionic surfactants without antimicrobial moieties

Correct Answer: Alcohols and quaternary ammonium compounds

Q38. What is the effect of adding EDTA (a chelating agent) to a formulation regarding microbial control?

• EDTA is a nutrient and increases microbial growth
• EDTA enhances the activity of some preservatives by chelating divalent cations
• EDTA sterilizes the product
• EDTA increases water activity

Correct Answer: EDTA enhances the activity of some preservatives by chelating divalent cations

Q39. Which test differentiates between total viable count and presence of specific pathogens in non-sterile products?

• Aerobic plate count for TVC and selective media for specific pathogens
• LAL test for total viable count
• pH strip test
• Weight variation test

Correct Answer: Aerobic plate count for TVC and selective media for specific pathogens

Q40. What role do preservative partitioning and distribution between phases play in emulsified products?

• They are irrelevant as preservatives only act on the oil phase
• Proper partitioning ensures preservative presence in the aqueous phase where microorganisms grow
• Partitioning increases viscosity only
• They affect only color stability

Correct Answer: Proper partitioning ensures preservative presence in the aqueous phase where microorganisms grow

Q41. Which microorganism can grow in highly acidic environments (pH <3) and is therefore problematic in acidic syrups if preservatives fail?

• Escherichia coli
• Acetobacter species
• Lactobacillus plantarum
• Gluconobacter spp.

Correct Answer: Acetobacter species

Q42. Which of the following is NOT an expected consequence of microbial spoilage in parenteral products?

• Fever and sepsis in patients
• Visible particulates, turbidity or gas in vials
• Increase in potency of the active drug
• Endotoxin contamination causing pyrogenic responses

Correct Answer: Increase in potency of the active drug

Q43. For an aseptically filled sterile product, a key environmental monitoring parameter to prevent microbial spoilage is:

• Frequency of employee breaks
• Viable particle counts in critical zones
• Color of the uniform
• Type of fluorescent lighting used

Correct Answer: Viable particle counts in critical zones

Q44. Which physical preservation method is most suitable for reducing microbial load in heat-sensitive liquid pharmaceuticals?

• Steam sterilization at 121°C
• Membrane filtration (sterile filtration)
• Dry heat at 160°C
• Gamma irradiation at industrial doses only

Correct Answer: Membrane filtration (sterile filtration)

Q45. The phenomenon where preserved products lose antimicrobial activity over time due to adsorption to packaging surfaces is called:

• Leaching
• Adsorptive loss or preservative sorption
• Osmotic imbalance
• Photodegradation

Correct Answer: Adsorptive loss or preservative sorption

Q46. Which of the following best describes cross-contamination risk leading to spoilage in a manufacturing line?

• Transfer of viable microorganisms from one batch/area to another due to improper cleaning or poor personnel practices
• Only the transfer of chemicals between products
• Occurrence only during packaging of solid doses
• Isolated to laboratory waste handling

Correct Answer: Transfer of viable microorganisms from one batch/area to another due to improper cleaning or poor personnel practices

Q47. Which storage test helps assess long-term microbial stability of a formulation under accelerated conditions?

• Disintegration test
• Accelerated stability study with periodic microbial limit testing
• Immediate-release dissolution test
• Assay by HPLC only

Correct Answer: Accelerated stability study with periodic microbial limit testing

Q48. Which microorganism is a common cause of contamination in nasal sprays and can survive in preservative systems if resistant?

• Nocardia asteroides
• Staphylococcus aureus
• Pseudomonas aeruginosa
• Clostridium tetani

Correct Answer: Pseudomonas aeruginosa

Q49. When selecting preservatives for a formulation containing high levels of surfactants, what must formulators consider?

• Surfactants never interact with preservatives
• Surfactants may solubilize or complex preservatives, reducing their free active concentration and efficacy
• Surfactants always increase preservative potency
• Only the fragrance is affected

Correct Answer: Surfactants may solubilize or complex preservatives, reducing their free active concentration and efficacy

Q50. Which of the following strategies is most comprehensive for minimizing microbial spoilage risk in finished pharmaceutical products?

• Rely solely on high preservative concentrations
• Implement integrated controls: good manufacturing practices, raw material control, preservative selection, packaging, and environmental monitoring
• Skip environmental monitoring if operators are trained
• Store all products refrigerated regardless of stability data

Correct Answer: Implement integrated controls: good manufacturing practices, raw material control, preservative selection, packaging, and environmental monitoring

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