Study guide ch. 3 Flashcards
All about the how to's
Which microscope uses visible light as its source of illumination?
Brightfield
What are the 3 sets of lenses used by a brightfield microscope?
Objective, ocular, and condenser
Which microscope provides a detailed 3d view of microbes and can study the structures of intact cells and viruses?
Scanning electron microscope
What are the characteristics of fluorescent microscopes?
- Uses UV source of illumination
- stains organisms using fluorescent dyes
- fluorescent substances absorb UV light and emit visible light
Which microscope is mainly used for spirochetes?
Darkfield
What do you need to do to the specimen before you view it in a transmission electron microscope?
Specimen must be fixed, dehydrated, and viewed under vacuum (shrinkage and distortion may occur)
What is a chromophore?
Molecule that absorbs light at a specific wavelength
What charge do basic and acidic dyes have?
Cationic basic
Anionic acidic
What charge do bacteria have at pH 7?
Sightly negative
What are basic dyes and acidic dyes used for
- Basic: used to highlight entire organism and structures
- Acidic: used to stain background
Crystal violet, methylene blue, and safranin are all what kind of dyes?
Basic
Eosin, Nigrosine, and India ink are all what kind of dyes?
Acidic
When the microbe repels the dye and stains the background, it is called _______.
Which dye is used in this?
- Negative staining
- Acidic dyes
What structures can you observe under negative staining?
- Viruses
- Bacteria
- Bacterial flagella
- Biological membrane structures and proteins or protein aggregates
What is a simple stain?
What are examples of simple stains?
- One dye is used, and it reveals the shape, size, and arrangement
- Methylene blue, carbolfuchsin, crystal violet, and safranin
What does a mordant do?
Increase affinity of a stain for specimen and coats a structure to make it thicker
What 2 groups does the gram stain divide the bacteria?
Gram positive + and gram negative -
Explain the gram stain step by step
- Crystal violet and iodine can go through thick cell wall
- Once inside form a complex (CV-I) which cannot go out of the cells
- Gram + bacteria will stain purple due to trapped CV-I complex
- Gram – bacteria will be colorless due to alcohol wash disrupting the lipopolysaccharide and allow CV-I complex to be washed out of the cell
- Gram – bacteria are pink due to counterstain with safranin
- Gram stain most consistent when used on young growing bacteria
Why do gram positive bacteria stain the way they do with gram stain?
They stain purple because of the trapped CV-I complex
Why do gram negative bacteria stain the way they do with gram stain?
They are colorless because the alcohol wash disrupts the lipopolysaccharide and allow the CV-I Complex to be washed out of the cell.
Why is it Important to know if a disease is caused by a gram positive or gram negative organism?
It provides info on how to treat the disease.
- gram positive bacteria is easily killed by penicillin and sulfonamide drugs
- gram negative bacteria are resistant to those drugs, but more susceptible to streptomycin, chloramphenicol, and tetracycline.
What does the acid- fast stain bind to in the bacteria?
It binds to the waxy material in their cell walls
What 2 genera of bacteria do the acid-fast stain identify?
- Mycobacterium
- Nocardia
What are endospores?
- dormant, tough, and non reproductive structure produced by certain bacteria from firmicute phylum
What are 3 genera of bacteria that produce endospores?
- Bacillus
- Clostridium
- Sporosarcinae
What is heat fix and why do you heat fix samples.
- It is a bacterial smear on a microscope slide that is passed briefly over a flame
- It is used to kill the bacteria and fix them into place
What is differential staining?
Using a primary stain and counter stain to distinguish cell types or parts (eg. gram stain, acid-fast stain, endospores)
What is structural staining?
Stains that reveal certain parts not revealed by conventional methods (capsule and flagellation stains)
