micro lab midterm Flashcards
- The term erythema, erythematous, relates to?
A reddening of the skin of the face that intensifies when exposed to the sun is characteristic of
Erythema Infectiosum
- What is the importance of the Gram stain? What’s the target structure? It’s based on what?
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
- Do biological membranes have an electric charge?
Yes, biological membranes typically have an electric charge due to the presence of charged phospholipids and proteins.
- How to differentiate Gram-positive and Gram-negative bacteria after preparing the Gam stain?
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.
- What is the purpose of practicing Aseptic techniques in microbiology?
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
- What is the critical step in the Gram stain?
Decolorizing Agent
- In microbiology, what is the purpose of microbial isolation on solid media?
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.
- What is Starch?
An unbranched polymer composed of simple sugars is a(n)
Starch
- What are the components of Glucose Phenol red broth, and what is the use of the media?
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).
- What is/are the cellular targets of non-ionizing radiation like UV?
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.
- What are the steps and reagents used in the Gram stain?
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.
- Transferring a microbe sample from one medium to another is?
Inoculation – the process of transferring a microbe from one medium to the next
Inoculum – the sample being transfered
- Borrelia burgdorferi, the etiological agent of Lyme disease, is an example of a Coccus?
False – it’s a spirochetes
- Identify D:
- What are heterocysts and akinetes, their function?
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
- Which organisms produce spores, and which do not?
Mainly Gram-positive bacteria like Bacillus and Clostridium produce spores; most other bacteria do not.
- What features of a microbe can be determined using a simple staining technique?
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).
- What are the genus and species of the samples presented of bacteria and fungi?
- Identify the staining technique used in the sample presented.
- The capsule in bacteria can be heated without consequences?
- Be prepared to identify growth patterns in slant media
- Follow proper aseptic technique when obtaining a sample growing in agar media.
- Approved equipment to attain sterilization in the lab
A Lethal Scratch”, relates to what part of her body?
- What are the expected results of a negative staining technique?
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.
- What feature of bacteria is distinguished in the Gram stain?
Cell wall
The Gram stain works because of differences in the ________ of bacteria.
Cell walls
- Be ready to document alpha, beta, and gamma hemolysis.
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
- Details of hand-washing.
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
- Which lab components must be monitored regarding lab safety hazards?
Chemicals, biological agents, sharp objects, and fire hazards.
- Humans and microbes.
Can be neutral (no harm or benefit), positive (e.g., probiotics), or negative (e.g., pathogenic infections).
- Bacterial populations case calculation
Calculations typically involve estimating colony-forming units using serial dilutions.
- How to achieve a successful streak plate isolation technique?
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.
- Microbiologists commonly view specimens in the lab with?
The microscope preferred for viewing living specimens is the ________ microscope.
Phase-Contrast
- Acidic dyes are useful for?
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.
- Which of the optic components of a brightfield microscope are magnifying lenses?
Objectives and Ocular Lens
- When using the aseptic technique in the lab, what rules should be followed?
Sterilize tools before use, handle samples carefully, minimize exposure to air, do not contaminate sterile surfaces.
- A process in microbiology used to prevent contamination by airborne spores, microorganisms, and surface contaminants.
Radiation – UV-C
- 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?
Simple staining, all cells appear blue, showing cell morphology without differentiating types.
- What is Safranin and its applications?
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
- When you place a petri plate in the incubator, you should
Should be placed upside down to prevent condensation on the agar surface.
- What is the use of the fine adjustment knob on the microscope?
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.
- When the magnification increases, the actual size of the field of view
The actual size of the field of view decreases as magnification increases.
- When using the high-power objective, you should not adjust the…
Coarse Adjustment Knob
- What’s the function of the diaphragm, and where is it located?
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.
- The generation time of bacterial cells is shortest during the ________ phase.
Log
- Does the endospore stain reveal internal structures within cells of the genera Bacillus and Clostridium?
The endospore stain reveals internal structures within cells of the genera Bacillus and Clostridium.
TRUE
- 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?
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
- 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?
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
- 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”?
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
A(n) ________ is a virus that infects bacterial cells.
Bacteriophage
The Gram stain works because of differences in the ________ of bacteria.
Cell Wall
- 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?
Acid-fast cells such as Mycobacterium lose the color of the primary stain in the presence of hydrochloric acid.
False
- Microbial cells that use organic carbon and obtain energy from light, are? What are photoheterotroph, chemoautotroph, photoautotroph, chemoheterotroph, lithoautotroph
A cell that uses an organic carbon source and obtains energy from light would be called a
Photoheterotroph
- Acidic dyes are commonly used for ?
Acidic dyes are commonly used for ________ stains.
Negative
- What is Carbolfuchsin, and when is it used?
Carbolfuchsin is the ________ in the acid-fast stain.
Primary Stain
Carbolfuchsin is a dye used in ________ stain(s).
Both acid fast and flagellar
- If a microbiology lab technician left the safranin out of the Gram stain procedure, what would be the result?
Gram positive cells would be purple and gram negative cells would be colorless
- 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.
TRUE
- The microscope that has a series of objective lenses and the one routinely used in a microbiology lab is called?
Binocular Compound Light Microscope
- Where does a clinical sample labeled as “sputum” originate?
A clinical sample labeled as “sputum” was collected from
The lungs
- Which of the following classification methods relies on the morphology of organisms?
Physical Characteristics
- In the Gram stain procedure, alcohol serves as a
(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.
- In a compound microscope, what is the lens that directs light through the specimen?
In a compound microscope, the lens that directs light into the eye is the
Ocular
- A microbe that grows only at the bottom of a tube of thioglycolate medium is probably a(n)
A microbe that grows only at the bottom of a tube of thioglycollate medium is probably a(n)
Obligate Anaerobe
- What is the function of Iodine in the Gram stain procedure?
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.
