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
How does the flagella stain work?
Treating the cells with tannic acid salts to increase the thickness of flagella –>subsequent stain with basic fuchsin –>flagella visible in the light microscope
What is the nucleus stained with?
Feulgen stain
How does the spore stain work?
The spore wall is relatively impermeable so they can be observed as colourless areas in cells stained by conventional stains
To stain spores, malachite green or carbolfuchshin are applied with heat –> the vegetative part of the cell can be stained with another counterstain after the decolorization step
How does the capsule stain work?
Capsules are usually demonstrated by modified negative staining
WELCH method –> treat the cells with hot crystal violet solution –> rinsing with copper sulfate solution (remove excess crystal violet and give a dark colour to the background)
What are the two different types of media that bacteria grow on?
-Defined medium: in which the exact chemical composition is known
-Complex medium: in which the exact chemical constitution of the medium is not known
How does non-selective media work?
It supports the growth of many different bacterial species without selection. Such as blood agar and chocolate agar media
How does selective media work?
They are used to eliminate (or reduce) the large numbers of irrelevant bacteria in the specimens
-It had an inhibitory agent that specifically selects against the growth of irrelevant bacteria
What are some examples of inhibitory agents of selective media?
-Sodium azide: selects for Gram + over Gram - bacteria
-Bile salts: select for Gram - enteric bacteria that inhibit Gram-mucosal and most Gram bacteria
-Colistin and nalidixic acid: inhibit the growth of many Gram - bacteria
What are two examples of selective media?
-MacConkey agar: which selects for the Enterobacteriaceae
-CNA blood agar (has colistin and nalidixic acid) that selects for Staphylococci and Streptococci
What is differential media?
Used to differentiate between bacterial groups
Some bacteria produce characteristic pigments, and others produce zones of clearing surrounding colonies
Examples of differential media:
Zones of hemolysis in the blood agar plate. Useful in classifying streptococcal species
A) complete hemolysis of RBCs –> Beta- hemolysis (Ex. streptococcus pyogenes)
B) Partial hemolysis –> Alpha-hemolysis (Ex. S. pneumonia)
C) No hemolysis —> Gamma-hemolysis
What is a biochemical test?
It is a test used for identification of bacteria species based on the differences in the biochemical activities of different bacteria
The bacterial species can be divided or classified into subgroups based on the ________ _______
immunological reactions
Immunological reactions are based on antibodies that react with specific bacterial cell surface structures such as:
lipopolysaccharide (LPS) (O antigen), flagella (H antigen), or capsular antigens (K antigen)
How is subtyping accomplished?
By serotyping, biotyping, antimicrobial susceptibility testing, and bacteriophage typing
What is an example of diplococcus bacteria?
Neisseria
What is an example of a tetrad?
Micrococcus
What is an example of cuboidal manner bacteria?
Sarcinia
What are 3 examples of long chain of cocci bacteria?
Streptococcus, enterococcus, Lactococcus
What is an example of irregular, grapelike clumps of bacteria?
Staphylococcus
What is an example of single rod bacteria?
Bacillus cerus
What is an example of diplobacilli?
Moraxella bovis
What is an example of chain of bacilli
Streptobacilli
What is an example of short bacilli (coccobacilli)?
Haemophilus influenzae
