micro lab midterm

Question 1

1. The term erythema, erythematous, relates to?

Answer 1

A reddening of the skin of the face that intensifies when exposed to the sun is characteristic of
Erythema Infectiosum

Question 2

2. What is the importance of the Gram stain? What’s the target structure? It’s based on what?

Answer 2

A gram stain is a differential stain that differentiates by color two major groups of bacteria: gram-positive and gram-negative. The response of cells to this staining technique is based on the composition of the cell wall.

The gram stain technique involves the use of dyes/stains, a mordant, and a decolorizer.
Identification of bacteria in the laboratory usually begins with the ________ for placement in one of two large groups of bacteria.
Gram Stain
In Gram staining, ethanol-acetone is used as a
Decolorizing Agent

Question 3

3. Do biological membranes have an electric charge?

Answer 3

Yes, biological membranes typically have an electric charge due to the presence of charged phospholipids and proteins.

Question 4

4. How to differentiate Gram-positive and Gram-negative bacteria after preparing the Gam stain?

Answer 4

The cell wall of gram-positive cells is made up of a very thick layer of peptidoglycan. The cell wall of gram-negative cells consists of a very thin layer of peptidoglycan surrounded by an outer membrane containing lipopolysaccharide. When viewed at oil immersion, gram-positive cells will appear purple and gram-negative cells will appear pink.

Question 5

5. What is the purpose of practicing Aseptic techniques in microbiology?

Answer 5

The method of handling microbes and materials in a way that minimizes contamination is called aseptic technique. This will prevent contamination of the sample, others, the environment, or yourself.
Proper usage of aseptic technique will prevent contamination of experimental media.

Aseptic means

Free of pathogens

Question 6

6. What is the critical step in the Gram stain?

Answer 6

Decolorizing Agent

Question 7

7. In microbiology, what is the purpose of microbial isolation on solid media?

Answer 7

Most laboratory work done with bacteria requires pure cultures of a single organism, so the members of mixed populations must be separated from each other in some way.

Question 8

8. What is Starch?

Answer 8

An unbranched polymer composed of simple sugars is a(n)
Starch

Question 9

9. What are the components of Glucose Phenol red broth, and what is the use of the media?

Answer 9

Phenol red broth is a medium that is commonly used to determine the test organisms ability to utilize a specific sugar. Phenol red broth includes the pH indicator phenol red, the sugar of interest, salts, and peptone (soluble hydrolysate of protein).

Question 10

10. What is/are the cellular targets of non-ionizing radiation like UV?

Answer 10

Ultraviolet radiation (also known as nonionizing radiation) primarily kills by damaging DNA and RNA by effecting bonding relationships within the molecule.
A major example is the formation of thymine or cytosine dimers (bonds between two adjacent pyrimidines in the DNA strand) which can lead to mutations. UV light with a wavelength between 200 and 290 nanometers is the most lethal because these are the wavelengths that are absorbed the most by DNA.

Question 11

11. What are the steps and reagents used in the Gram stain?

Answer 11

The Gram stain technique involves the use of dyes/ stains, a mordant, and a decolorizer.
The first step is to make a heat-fixed smear. Crystal violet, the primary stain, is applied to the heat-fixed smear. Crystal violet is a basic stain and stains all of the cells on the slide purple. The slide is rinsed with water and then the smear is covered with Gram’s iodine. Gram’s iodine is a mordant. Mordants fix color into the cell or intensify color. In this case, the iodine binds to RNA and crystal violet in the cell, creating a very large color complex.
The next step is decolorization with acetone–alcohol. The slide is rinsed with acetone- alcohol. Acetone–alcohol is a solvent/denaturant. It creates large holes in the gram-negative cell’s outer lipopolysaccharide cell wall and washes out the iodine–crystal violet complex. The thick peptidoglycan layer in gram- positive cells retains the iodine–crystal violet complex. After the decolorization step, gram-negative cells are colorless and gram-positive cells are purple.
The final step is the application of the counterstain, safranin. The smear is then rinsed with water and blotted dry. When viewed at oil immersion, gram-positive cells will appear purple and gram-negative cells will appear pink.

Question 12

12. Transferring a microbe sample from one medium to another is?

Answer 12

Inoculation – the process of transferring a microbe from one medium to the next
Inoculum – the sample being transfered

Question 13

13. Borrelia burgdorferi, the etiological agent of Lyme disease, is an example of a Coccus?

Answer 13

False – it’s a spirochetes

Question 14

14. Identify D:

Question 15

15. What are heterocysts and akinetes, their function?

Answer 15

Akinetes are reproductive structures. They are large, usually about two to three times larger than the average cell in a filamentous strand. The akinete will have a thicker wall and a grainy, mottled appearance.

Heterocyst are thick-walled cells responsible for nitrogen fixation. Nitrogen is an essential element. All living things require nitrogen to synthesize nucleic acids and proteins. Heterocysts are thick-walled and very round, and have a smooth, even coloration.

Aerobic cyanobacteria carry out the reactions of nitrogen fixation in

Heterocysts
Spores known as akinetes are reproductive structures of
Members of the cyanobacteria

Question 16

16. Which organisms produce spores, and which do not?

Answer 16

Mainly Gram-positive bacteria like Bacillus and Clostridium produce spores; most other bacteria do not.

Question 17

17. What features of a microbe can be determined using a simple staining technique?

Answer 17

Simple stain techniques are done using basic stains, such as safranin or methylene blye, all of the cells on the slide are stained the same color.
It is useful for observing the morphology or shape and the arrangement of cells.
The three most common shapes of bacteria are: the bacillus (oblong, rod), coccus (sphere), and spirillum (comma-shaped spiral).

Question 18

18. What are the genus and species of the samples presented of bacteria and fungi?

Question 19

19. Identify the staining technique used in the sample presented.

Question 20

20. The capsule in bacteria can be heated without consequences?

Question 21

21. Be prepared to identify growth patterns in slant media

Question 22

22. Follow proper aseptic technique when obtaining a sample growing in agar media.

Question 23

23. Approved equipment to attain sterilization in the lab

Question 24

A Lethal Scratch”, relates to what part of her body?

Question 25

25. What are the expected results of a negative staining technique?

Answer 25

The dyes used in negative staining have an acidic chromogen (negatively charged chromophore) that is repelled by the bacterial cell. As a result, the cell remains uncolored and the background is stain. Negative slides are not heat-fixed, so cell shape and size are not distorted and can be accurately observed. Negative staining is particularly appropriate for visualizing delicate structures that are distorted by heat like capsules and cells like the spirilla and spirochetes.

Question 26

26. What feature of bacteria is distinguished in the Gram stain?

Answer 26

Cell wall
The Gram stain works because of differences in the ________ of bacteria.
Cell walls

Question 27

27. Be ready to document alpha, beta, and gamma hemolysis.

Answer 27

Streptococcus and Staphylococcus both make toxins called hemolysins that can break down red blood cells (RBCs).
Alpha-hemolysins cause partial lysis of RBCs, which lead to darkening of the blood agar around the colony called Alpha-Hemolysis. Hemoglobin breakdown causes the green color often seen in Alpha-Hemolysis. Ex: S. Pneumoniae
Beta-Hemolysins cause complete lysis of RBCs and breakdown of hemoglobin, which leads to colorless clearing of the blood agar around the colony called beta-hemolysis. Ex. S. Pyogenes
If an organism causes no hemolysis, it is reported as gamma-hemolysis. Ex. E. Faecalis

Question 28

28. Details of hand-washing.

Answer 28

You should wash your hands after, and even during, lab with antibacterial soap.
Semmelweis advocated handwashing as a method of preventing which of the following diseases?
Puerperal Fever

Question 29

29. Which lab components must be monitored regarding lab safety hazards?

Answer 29

Chemicals, biological agents, sharp objects, and fire hazards.

Question 30

30. Humans and microbes.

Answer 30

Can be neutral (no harm or benefit), positive (e.g., probiotics), or negative (e.g., pathogenic infections).

Question 31

31. Bacterial populations case calculation

Answer 31

Calculations typically involve estimating colony-forming units using serial dilutions.

Question 32

32. How to achieve a successful streak plate isolation technique?

Answer 32

The isolation streak plate is a widely used method to separate individual bacterial from mixtures.
Tips for success:
Touch your loop gently to the agar. Try to not dig in or cut the agar surface of the plate. When streaking your plate, hold the lid at an angle covering the plate or you may add some extra microbes to your mixture. Keep your plate in the incubator lid side down. If the lid is facing upward, water from condensation could drop onto the surface of your plate, which would very likely ruin your streak.

Question 33

33. Microbiologists commonly view specimens in the lab with?

Answer 33

The microscope preferred for viewing living specimens is the ________ microscope.

Phase-Contrast

Question 34

34. Acidic dyes are useful for?

Answer 34

Acidic dyes
Are negatively charged and work best at low pH

Negative staining is particularly appropriate for visualizing delicate structures that are distorted by heat like capsules and cells.

Question 35

35. Which of the optic components of a brightfield microscope are magnifying lenses?

Answer 35

Objectives and Ocular Lens

Question 36

36. When using the aseptic technique in the lab, what rules should be followed?

Answer 36

Sterilize tools before use, handle samples carefully, minimize exposure to air, do not contaminate sterile surfaces.

Question 37

37. A process in microbiology used to prevent contamination by airborne spores, microorganisms, and surface contaminants.

Answer 37

Radiation – UV-C

Question 37

39. A microbiologist prepares a fixed smear of bacterial cells and stains them with Loeffler’s methylene blue. All the cells appear blue under the oil lens. This is an example of?

Answer 37

Simple staining, all cells appear blue, showing cell morphology without differentiating types.

Question 38

38. What is Safranin and its applications?

Answer 38

Counterstain, the final step in gram-staining
Because gram-negative bacteria are colorless after decolorization, their presence is demonstrated by applying the counterstain safranin in the final step

Question 39

41. When you place a petri plate in the incubator, you should

Answer 39

Should be placed upside down to prevent condensation on the agar surface.

Question 39

40. What is the use of the fine adjustment knob on the microscope?

Answer 39

By rotating the fine focus adjustment knob, it is possible to bring the image into sharp focus. This knob raises and lowers the stage in very small increments.

Question 40

42. When the magnification increases, the actual size of the field of view

Answer 40

The actual size of the field of view decreases as magnification increases.

Question 41

43. When using the high-power objective, you should not adjust the…

Answer 41

Coarse Adjustment Knob

Question 42

44. What’s the function of the diaphragm, and where is it located?

Answer 42

Aperture Diaphragm Control – The diaphragm controls the amount of light entering the substage condenser from the light source. This is probably the most important mechanism for adjusting light. Set the diaphragm half open when using the 10x and 40x objectives. Open the diaphragm completely when using the oil immersion lens. Too much light can bleach out your specimen. You need to use the appropriate light level for each magnification.

Field Diaphragm Lever – This diaphragm opens and closes to increase and decrease light from the light source. This diaphragm should remain open.

Question 43

45. The generation time of bacterial cells is shortest during the ________ phase.

Answer 43

Log

Question 44

46. Does the endospore stain reveal internal structures within cells of the genera Bacillus and Clostridium?

Answer 44

The endospore stain reveals internal structures within cells of the genera Bacillus and Clostridium.

TRUE

Question 45

47. Two men may be the father of a child, according to a DNA fingerprint analysis. The figure shows a pattern of the probable alternatives. M is the mother, C is the child, A and B are the two men. Look at the evidence, and what is the correct interpretation of these results?

Answer 45

Two men may be the father of a child. Figure 8.2 shows the results of a DNA fingerprint analysis to determine paternity. M is the mother, C is the child, A and B are the two men. What is the best interpretation of these results?

The man identified as B is probably the father

Question 46

48. You are examining a bacterial smear on a light microscope. You observe pinkish-red bacilli and blue cells of various shapes. You are probably looking at a smear prepared with what type of staining?

Answer 46

You are examining a bacterial smear on a light microscope. You observe pinkish-red bacilli and blue cells of various shapes. You are probably looking at a smear prepared with the ________ stain.

Ziehl-Neelsen Acid-Fast

Question 47

49. Bacteria in the genus Salmonella are frequent causes of serious food contamination. Which of the following methods would provide rapid confirmation that a Salmonella species was a contaminant in food suspected of causing food “poisoning”?

Answer 47

Bacteria in the genus Salmonella are frequent causes of serious food contamination. Which of the following methods would provide rapid confirmation that a Salmonella species was a contaminant in food suspected of causing food “poisoning”?

Phage Typing

Question 48

A(n) ________ is a virus that infects bacterial cells.

Answer 48

Bacteriophage

Question 49

The Gram stain works because of differences in the ________ of bacteria.

Answer 49

Cell Wall

Question 50

52. Acid-fast stains work on cells such as Mycobacterium. What is the function of the acid when it loses the color of the primary stain?

Answer 50

Acid-fast cells such as Mycobacterium lose the color of the primary stain in the presence of hydrochloric acid.

False

Question 51

53. Microbial cells that use organic carbon and obtain energy from light, are? What are photoheterotroph, chemoautotroph, photoautotroph, chemoheterotroph, lithoautotroph

Answer 51

A cell that uses an organic carbon source and obtains energy from light would be called a
Photoheterotroph

Question 52

54. Acidic dyes are commonly used for ?

Answer 52

Acidic dyes are commonly used for ________ stains.

Negative

Question 53

55. What is Carbolfuchsin, and when is it used?

Answer 53

Carbolfuchsin is the ________ in the acid-fast stain.
Primary Stain

Carbolfuchsin is a dye used in ________ stain(s).

Both acid fast and flagellar

Question 54

56. If a microbiology lab technician left the safranin out of the Gram stain procedure, what would be the result?

Answer 54

Gram positive cells would be purple and gram negative cells would be colorless

Question 55

57. The process of immobilizing organisms on a glass slide and causing denaturation of their proteins through the application of heat is referred to as heat fixation.

Answer 55

TRUE

Question 56

58. The microscope that has a series of objective lenses and the one routinely used in a microbiology lab is called?

Answer 56

Binocular Compound Light Microscope

Question 57

59. Where does a clinical sample labeled as “sputum” originate?

Answer 57

A clinical sample labeled as “sputum” was collected from

The lungs

Question 58

60. Which of the following classification methods relies on the morphology of organisms?

Answer 58

Physical Characteristics

Question 59

61. In the Gram stain procedure, alcohol serves as a

Answer 59

(Textbook)
Solvent/Denaturant. It creates large holes in the gram-negative cells’ outer lipopolysaccharide cell wall and washes out the iodine-crystal violet complex.

Application of alcohol dissolves lipids in the outer membrane and removes the dye from the peptidoglycan later – only in the gram-negative cells.

Question 60

62. In a compound microscope, what is the lens that directs light through the specimen?

Answer 60

In a compound microscope, the lens that directs light into the eye is the

Ocular

Question 61

63. A microbe that grows only at the bottom of a tube of thioglycolate medium is probably a(n)

Answer 61

A microbe that grows only at the bottom of a tube of thioglycollate medium is probably a(n)
Obligate Anaerobe

Question 62

64. What is the function of Iodine in the Gram stain procedure?

Answer 62

Gram’s iodine is a mordant, mordants fix color into the cell or intensify color. In this case, the iodine binds to RNA and crystal violet in the cell, creating a very large color complex.

The mordant, iodine, is added in the second step. This is a stabilizer that causes the dye to form large complexes in the peptidoglycan meshwork of the cell wall. The thicker gram-positive cell walls are able to more firmly trap the large complexes than those of the gram-negative cells.