MICRO LAB

• What are safety precautions necessary for when working with chemicals and microorganisms?

  To ensure caution when handling chemicals, glass, hot water baths, and sharp instruments.
• Why is good aseptic technique important when handling microorganisms?

  It prevents contamination and ensures a clean working environment.
• What is the definition of a colony in microbiology?

  A mass of cells that grows from a single cell.
• What is the purpose of isolating colonies on an agar plate?

  To obtain pure cultures from mixed cultures.
• What are the objectives of proper laboratory and aseptic technique?

  • Restrict microorganisms to containers used for study
  • Prevent environmental microorganisms from entering specimens
• What should be done with personal items like books and coats in the laboratory?

  They must be kept away from lab tables and chairs.
• What is the proper procedure for handwashing before laboratory work?

  Wash hands with soap and warm water before and after work.
• What should be done in case of a culture spill in the laboratory?

  See the instructor for assistance.
• How should contaminated waste be disposed of in the laboratory?

  Contaminated waste goes into autoclavable bags.
• What must be labeled when placed in the refrigerator or incubator?

  Everything must be labeled with name and other data.
• What is the correct method for transferring cultures across the room?

  All transfers should be done over the laminar flow hood.
• What is prohibited in the laboratory regarding food and drink?

  No food or drink is allowed in the laboratory.
• Why should long hair be tied back in the laboratory?

  To avoid hazards and prevent contamination.
• What are the precautions for aseptic technique in handling microbes?

  • Flaming inoculating loops and needles
  • Preventing splattering
  • Flaming mouths of test tubes
  • Proper disposal of contaminated instruments
  • Cleaning work area before and after use
• What is the simplest technique to isolate bacteria from mixed culture?

  The streak plate technique.
• What happens during the streak plate technique?

  A loopful of bacteria is streaked across the surface of an agar plate.
• What should you do after streaking the agar plate?

  Incubate the plate for 1-2 days.
• What is the purpose of flaming the inoculating loop?

  To sterilize the loop before and after use.
• What are the characteristics to observe in colony morphology?

  • Shape
  • Size
  • Edge
  • Elevation
  • Consistency
  • Pigmentation
  • Odor
• What is the appearance of Staphylococcus aureus colonies?

  Size 2-3 mm, circular shape, entire edge, convex elevation, buttery consistency, gold pigmentation.
• What is the appearance of Proteus vulgaris colonies?

  Size 1-3 mm, irregular shape, irregular edge, flat-raised elevation, mucoid consistency, colorless-light red/brown pigmentation.
• What is the significance of recognizing colony morphology?

  It aids in the identification and classification of organisms.
• What are the growth patterns observed in broth cultures?

  1. Clear
  2. Turbid
  3. Pellicle
  4. Flocculant
  5. Sediment
• What should be done if you do not flame your loop between thirds of the plate?

  It can lead to cross-contamination.
• What should you observe for signs of growth in broth cultures?

  Signs of growth include turbidity or cloudiness.
• What are the different distributions of growth in broth cultures?

  1. Clear - no obvious growth.
  2. Turbid - growth throughout the media.
  3. Pellicle - growth concentrated at the top.
  4. Flocculant - flaky masses of growth.
  5. Sediment - mass settles at the bottom.
• Why is it useful to know the growth pattern of an organism on agar slant or broth medium?

  It aids in the identification and classification of organisms.
• What could happen if you do not flame your loop between thirds of the plate?

  Cross-contamination may occur, leading to mixed cultures.
• Why do you pass the mouth of the tube through the flame?

  It sterilizes to prevent contamination.
• Why is a streak plate used to grow a bacterium instead of an agar medium slant or broth medium?

  A streak plate allows for better isolation of individual colonies.
• What should you understand after completing the growth curve and serial dilutions exercise?

  • How bacteria are counted in the laboratory.
  • How to perform a viable plate count to generate a growth curve.
• What is the viable plate count method used for?

  It gives a count of the viable or live cells in a solution.
• What is the purpose of performing serial dilutions in the viable plate count?

  To determine the growth kinetics or curve for a microbe.
• What materials are needed for the viable plate count exercise?

  4 Tryptic soy broth plates, 4 empty sterile petri plates, and dilution tubes.
• How should you read the lines on the various sizes of pipettes?

  The reading is taken at the bottom of the meniscus.
• What is the procedure for making dilution sets?

  1. Prepare dilution blanks with specified amounts of water.
  2. Transfer specified volumes of blue water into dilution tubes.
  3. Mix the tube contents thoroughly.
• What is the dilution factor for transferring 0.5 ml into 4.5 ml of water?

  The dilution factor is $\frac{0.5}{0.5 + 4.5} =$$\frac{1}{10}$.
• What is the total dilution factor for the second tube in dilution set 1?

  The total dilution factor is $\frac{1}{100}$.
• What are the identifiable portions of a standard growth curve?

  1. Lag Phase - cells adapt; no increase in number.
  2. Log Phase - rapid cell division; exponential growth.
  3. Stationary Phase - growth rate slows; new cells equal dying cells.
  4. Death Phase - viable cells decrease.
• What does the slope during the log phase indicate?

  The slope indicates the growth rate of the culture.