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CFTRI M.Sc. (Food Technology) Microbiology Flashcards
51 question-and-answer cards covering Microbiology as it is examined in CFTRI M.Sc. (Food Technology). 24 of them are printed below, taken from across the deck — no signup, no paywall on the preview.
24 sample cards from the Microbiology deck
Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.
Why do Gram-positive bacteria retain crystal violet while Gram-negative do not?
The thick peptidoglycan of Gram-positives dehydrates and traps the crystal violet-iodine complex during decolorization; the thin wall plus lipid outer membrane of Gram-negatives lets the complex wash out, so they take up the counterstain.
What is the role of the mordant (iodine) in the Gram stain?
Iodine combines with crystal violet to form a larger, insoluble crystal violet-iodine (CV-I) complex that is harder to wash out of the cell.
What is the most critical and error-prone step of the Gram stain?
Decolorization with alcohol/acetone; over-decolorizing makes Gram-positives appear Gram-negative, and under-decolorizing makes Gram-negatives appear Gram-positive.
What does the acid-fast (Ziehl-Neelsen) stain detect and which organisms are acid-fast?
It detects cells with waxy mycolic-acid-rich walls; Mycobacterium and Nocardia are acid-fast (appear red); non-acid-fast cells appear blue from the methylene blue counterstain.
What is negative staining and what is it used for?
Staining the background with an acidic dye (e.g., nigrosin/India ink) while the cell stays unstained; used to visualize capsules and to view cells without heat-fixing distortion.
Which stain is used to demonstrate bacterial endospores, and what are its main reagents?
The Schaeffer-Fulton spore stain: malachite green (primary stain, driven in with heat) and safranin (counterstain); spores appear green, vegetative cells red/pink.
What is the purpose of heat fixation before simple/differential staining?
It kills and adheres cells to the slide, preserves morphology, and makes them more permeable to the stain (prevents washing away).
Define a food contaminant.
Any biological, chemical, or physical agent or foreign matter not intentionally added to food that may compromise its safety or quality.
Name the three main categories of food contamination hazards.
Biological (bacteria, viruses, molds, parasites), chemical (toxins, pesticides, heavy metals, cleaning agents), and physical (glass, metal, hair, stones).
What is cross-contamination and how is it prevented?
The transfer of harmful microbes from one food/surface to another (e.g., raw to cooked); prevented by separating raw and cooked foods, using separate utensils/boards, handwashing, and sanitizing surfaces.
Differentiate food infection from food intoxication.
Food infection results from ingesting live pathogens that grow in the body (e.g., Salmonella); food intoxication results from ingesting a preformed toxin in the food (e.g., Staphylococcus aureus, Clostridium botulinum).
What organism causes botulism and what conditions favor it?
Clostridium botulinum; it is anaerobic, spore-forming, and produces a potent neurotoxin in low-acid (pH > 4.6), low-oxygen canned/preserved foods.
What are the seven principles of the HACCP food safety system?
1) Conduct hazard analysis, 2) Determine critical control points (CCPs), 3) Establish critical limits, 4) Establish monitoring, 5) Establish corrective actions, 6) Establish verification, 7) Establish record-keeping/documentation.
What is the 'temperature danger zone' for bacterial growth in food?
Approximately 5 degrees C to 60 degrees C (about 40-140 degrees F), the range in which pathogenic bacteria multiply most rapidly.
What is water activity (aw) and why does it matter for food safety?
Water activity is the ratio of the vapor pressure of water in food to that of pure water (0-1); lowering aw inhibits microbial growth. Most bacteria need aw above ~0.91, most molds above ~0.80.
What are the main objectives/principles of food preservation?
To prevent or delay microbial decomposition, prevent self-decomposition (enzyme/autolysis) and chemical changes (oxidation), and prevent damage from insects, pests, and physical/mechanical injury.
What is the difference between asepsis and the removal of microorganisms as preservation principles?
Asepsis means keeping out (preventing entry of) microorganisms, e.g., packaging; removal means physically taking microbes out, e.g., filtration, washing, centrifugation.
How does high temperature preserve food, and what is the difference between pasteurization and sterilization?
Heat destroys microbes and enzymes. Pasteurization is mild heat killing pathogens/vegetative cells (food not sterile, e.g., HTST milk 72 C/15 s); sterilization (e.g., canning/UHT) destroys all microbes including spores for commercial sterility.
How does low temperature preserve food, and what is the difference between chilling and freezing?
Low temperature slows microbial growth and enzyme activity (it preserves, not sterilizes). Chilling/refrigeration (0-5 C) slows growth; freezing (below -18 C) stops growth by removing available water as ice.
How does drying/dehydration preserve food?
It lowers water activity below the level needed for microbial growth and enzyme action, inhibiting bacteria, yeasts, and molds.
How do salt and sugar act as chemical preservatives?
High concentrations of salt or sugar lower water activity and create osmotic pressure that draws water out of microbial cells (plasmolysis), inhibiting their growth.
How does food irradiation preserve food and what are the dose-based categories?
Ionizing radiation (gamma rays, X-rays, electron beams) damages microbial DNA. Radurization (low dose, shelf-life extension), radicidation (medium dose, kills non-sporing pathogens), radappertization (high dose, commercial sterility).
What is the role of lowering pH (acidity) and fermentation in food preservation?
Low pH inhibits most spoilage and pathogenic microbes; fermentation by lactic acid bacteria produces acids (and sometimes alcohol/bacteriocins) that preserve food, as in curd, pickles, and sauerkraut.
What are the hurdle technology and the canning-relevant D-value and 12D concept in preservation?
Hurdle technology combines several mild preservation factors (pH, aw, temperature, preservatives) to inhibit microbes. The D-value is the time to reduce a population 10-fold at a set temperature; the 12D process (botulinum cook) reduces C. botulinum spores by 12 log cycles to ensure safe low-acid canned foods.
What this deck covers
The Microbiology deck follows the CFTRI M.Sc. (Food Technology) Microbiology syllabus — 7 chapters and 5 topics — so questions land on material that is genuinely examinable rather than trivia around it. That works out to roughly 7.3 cards per chapter.
Answers are written to be recallable, not just readable — averaging about 186 characters, which is long enough to carry the reasoning and short enough to say out loud.
A deck like this earns its keep on the second and third pass. Read the syllabus first so you know the shape of the subject, then use the cards to find the specific facts that have not stuck.
Microbiology flashcards FAQ
How many Microbiology flashcards are in this CFTRI M.Sc. (Food Technology) deck?
51 cards. This page previews 24 of them, sampled evenly across the deck so you can judge the difficulty before installing anything.
Are these CFTRI M.Sc. (Food Technology) flashcards free?
Yes. The preview here is free to read with no signup, and the full 51-card deck is free inside the Examius app.
What do the Microbiology cards cover?
They follow the CFTRI M.Sc. (Food Technology) Microbiology syllabus — 7 chapters and 5 topics — so the questions track what is actually examinable.
How should I use these flashcards?
Read the syllabus first so you know the shape of the subject, then drill the deck. Examius schedules each card with spaced repetition, so cards you keep missing come back sooner and ones you know drift further apart.