Lecture 5 Flashcards
What is bacterial taxonomy?
Is the classification of organisms in an ordered system that indicates a natural relationship
What are the three areas of bacterial taxonomy?
-Identification: is the practical side of taxonomy, the process of determining that a particular isolate belongs to a recognized taxon.
-Classification: is the categorization of organisms into taxonomic groups based on mutual similarities, genetics, and evolutionary resources
-Nomenclature: refers to the naming of an organism by an established group of scientific medical professionals
What 4 things can bacteria be classified by?
- Morphological characteristics
- Physiological and metabolic characteristics
- Biochemical characteristics
- Ecological characteristics
How do you name a bacteria?
-The first part is the generic name (the genus)
-Second part is the species name
Name of the microorganism should be italicized or underlined
Genus is CAPITALIZED (written first)
Species is lowercase
Most common bacterial shape is:
cocci, roughly spherical cells
What is the second most common bacterial shape?
rod shape, bacilli
-single
-diplobacili
-streptobacilli (chain of bacilli)
-coccobacilus (short bacilli)
Are corkscrew bacteria that can range from a gently curved shape to a corkscrew-like spiral
Spirilla (spirillum)
What are the 3 types of spirilla and an example of each?
- Vibria: Vibrio chloerae
-Spiral: Campylobacter jejuni, Helicobacter pylori
-Spirochete: Treponema pallidum
What is used to identify bacteria?
Staining and microscopy:
How does a light (brightfield) microscope work?
-Direct examination of stained or unstained preparations by light microscopy
-particularly useful for the detection of bacteria, fungi, and parasites. Even the smallest bacteria can be visualized
-The resolution limit of the light microscope is near 0.2 um
How does a dark-field microscope work?
A black background is created by blocking the central light
-Resolution is high -> useful for observing very small bacteria such as Treponema pallidum
How does a fluorescence microscope work?
It is similar to the dark-field microscope, except that the light source is ultraviolet and the organisms are stained with fluorescent compounds
The specimen is seen as a halo around only the organism tagged with fluorescent compounds
What are the two general classes of ionizable dyes?
-Basic dyes: such as methylene blue, basic fuchsin, crystal violet, safranin, and malachite green. They have positively charged groups that can bind to negatively charged structures such as DNA and cell membrane
-Acid dyes: such as eosin, rose bengal, and acid fuchsin, They are negatively charged groups and can stain positively charged cell proteins and organelles.
How does gram stain work?
- Apply a basic dye (crystal violet) and iodine solution (all bacteria will be stained blue) at this point in the procedure
-Decolorization step: the cells are treated with alcohol (Gram-positive cells retain the crystal violet-iodine complex, remaining blue). Gram-negative cells are completely decolorized by alcohol.
-A counterstain safranin (red dye) is applied so that the decolorized Gram-negative cells will be stained red and Gram-positive cells appear purple
What is an acid-fast stain?
Used to stain bacteria that do not simply stain with regular procedure
-The acid-fast bacteria take the red colour of carbolfuchsin dye, while the non acid-fast bacteria take the colour of the counterstain (blue or green)
-The method is mainly used to stain Mycobacterium tuberculosis, Myocobacterium leprosy, and Actinomycetes bacteria
