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How would you recognize microbial growth in a liquid media? What about a solid media?
In liquid: medium will have precipitation in it.
In solid: colonies will form
What is a colony? What is the relationship between a cell and a colony?
A cell is a unit of a colony. A colony has millions of cells. A colony can be seen by the naked eye, but a cell needs a microscope.
What additional information does a solid culture provide compared to a liquid culture?
A solid culture is a a differential medium in which the colors differentiate the different microbes. The microbes look the same in a liquid medium.
What are some characteristics of bacterial and fungal colonies that can be used to differentiate between the two?
Bacterial colonies looks like little dots and has color. Fungal colonies are furry/fuzzy with hyphae
In positive pressure rooms, the air pressure is _____ than that found in the adjoining corridor.
matter, as saliva mixed with mucus or pus, expectorated from the lungs and respiratory passages.
Explain what is meant by a false positive result. How does this differ from a false negative result?
A test result which indicates that an individual is affected when he or she is actually unaffected; ie, a positive test result in a truly unaffected individual. A false negative is tested negative, but they do have the disease.
What will happen if a hot inoculating tool is plunged into a media containing bacteria?
An aerosol may be created, releasing bacteria into the air.
When bacterial growth is being removed from a liquid culture, which inoculating tool is used?
When bacterial growth is being removed from a solid culture(slant or plate), which inoculating tool is used?
In the "TB" case, how did contamination most likely occur?
Not using aseptic techniques, poor handling of a the test culture which allowed cross contamination.
single species is isolated from other species in the population (opposite of mixed culture)
What is the difference between a pure culture and a mixed culture?
A pure culture contains one cell and a mixed culture contains many cells.
How can a pure or mixed cutlure become contaminated? How can this be prevented?
They become contaminated when another unwanted microbe goes into the medium. This can be prevented by aseptic techniques.
What is the streak-plate method?
This method is the most economical in terms of time and materials, requiring just a few minutes and only a single plate of media.
What is the loop dilution method?
This method consumes more time and materials than does a streak plate, but the results produced, even by the beginning student, are generally quite good.
What is the spread-plate method?
This method gives consistently reliable results when bacterial samples are dilute or if the medium being inoculated is highly selective.
What is the importance of generating isolated bacterial colonies?
To be sure that only one cell is being examined and that it is a pure culture.
What is the purpose of subcultiring bacterial isolates?
allows easier study and organization of bacterial isolates
What bacterium causes neonatal tetanus and where is it found?
Clostridium tetani (found in soil and animal feces)
Rod-shaped bacteria divide only along the transverse plane. Bacilli arrangements consists of:
diplobacilli, streptobacilli, and palisades
The characteristic arrangement of Corynebacterium cells resembling a row of fence posts and created by snapping.
Positive staining (simple staining) stains what?
The bacterial cell so that it appears as a darkly colored object against a light background.
Common basic (positively charged) stains in the microbiology laboratory:
methylene blue, crystal violet, malachite green, and safranin (which is pink)
What is one advantage of negative staining?
Has the most accurate determination of the size of a bacterial cell because it doesn't require heating(like positive staining), which shrinks the cell.
What is the order of Gram staining?
crystal violet(primary stain), Iodine(mordant), ethyl alcohol(decolorizer), safranin(counterstain
1. scientific study of the forms and structures of plants and animals 2. form and structure of an organism or any of its parts
cocci = spheres
bacilli = rods
vibrio = bent rods
spirilla/spirochetes = spiral shaped
The way a bacteria grow:
diplo = pairs (e.g. diplococcus are round and are found in pairs)
strepto = chains
staph = clusters
(biology) the appearance of two or more distinctly different forms in the life cycle of some organisms
The differences in values, colors, textures, shapes, and other elements within a presentation
What two staining techniques are appropriate for determining the shape and arrangement of a bacterial species?
Differential and Gram staining
What stains can be used for negative staining, and why can these same stains not be used for simple staining?
Negative staining needs negative charged acidic dyes(nigrosine or India ink) and positive staining needs positive charged dyes.
What is the difference between a simple stain and a differential stain?
Simple stain is a positive stain which stains a pure culture. Differential stain like the Gram stain, can be used to to a mixed culture.
Based strictly on cellular morphology, which bacterial species is most easily differentiated from the other? Why?
Staphylococcus aureus & Salmonella typimurium
They have different shapes and structures.
Gram-positives and Gram-negatives can be distinguished by color.
A small, dormant, resistant derivative of a bacterial cell that germinates under favorable growth conditions into a vegetative cell.
What is the use of acid-fast stains?
To detect members of the genus Mycobacterium, such as the pathogens M. tuberculosis and M. leprae which causes leprosy. Other bacterial species in the genus Nocardia and protozoan parasites (Cryptosporidium and Isospora). Only a few are acid-fast organisms.
Acid-fast bacteria contains what in their cell walls?
Mycolic acid - a waxy material which prevents stains from penetrating
What are the steps of Endospore staining?
malachite green(primary stain), heat(mordant), water(removes green dye from vegatative cells but not from endospores), safranin(counterstain vegatative cells and sporangium).
stains to react differently with different types of bacteria, used to distinguish bacterial types. Gram stain, acid-fast stain
Two diseases caused by acid-fast bacteria and the species related:
TB: Mycobacterium tuberculosis
Leprosy: Mycobacterium leprae
Four bacterial pathogens that form endospores and the disease associated with each:
Bacillus anthracis : Anthrax
Clostridium botulinum : paralysis muscles, food poisoning
Clostridium tetani : lockjaw
Clostridium perfringens : gas gangrene(blockage of blood supply)
What causes acid-fast cells to clump together?
Mycolic acid - a waxy material that prevents stains from penetrating
Why is anthrax also known as Woolsorter's disease?
Because anthrax initially started when human ingest spores from wool pelts.
What is secondary contamination?
radioactive contamination that has been transferred from one location to another, such as from hands to face or from a contaminated tool or from contaminated protective gear to one's skin; it can also refer to transfer from a contaminated individual to a second individual. Secondary contamination is often referred to as cross-contamination.
not easily decolorized by acid solutions; pertains to micro-organisms (especially the tubercle bacillus that causes tuberculosis), organisms that demonstrate a characteristic of having a high lipid content in their cell wall that resists drying, acids and various germicides?
don't have mycolic acid so they lose color during decolorization. to be visualized, must be counterstained with methylene blue
What makes staining endospores a challenge?
the protective nature of the endospore prevents the penetration of dye
Motile bacteria display...
chemotaxis, a complex movement of the cell toward nutritients or away from harmful substances
a procedure in which a small amount of liquid culture is placed on a microscope slide and covered with a cover glass
Problems from using a wet mount:
-tendency to dry out
-current movements that may mimic motility
-potential for contamination of instruments and self with pathogenic microbes
Hanging drop slide prevents these problems
Hanging drop slide
a cover glass is prepared with a small dab of petroleum jelly (Vaseline) on each corner and a single loopful of a liquid culture in the center
movement due to water currents, bombardment of cells by surrounding molecules, primarily water; causes cell to jiggle or shake
Why is speed imporatant in these techniques to find motility?
time and evaporation of the media will reduce bacterial motility while condensation forming on a hanging drop slide can reduce the clarity of the image
Why is understanding motility in a bacteria useful?
used as an aid in the identification of an isolate(to single out)
contains one or more ingredients that are not precisely known, often an extract of animals, plants, or yeast (most media in the lab); eg.trypticase soy agar and nutrient broth
a precisely known chemical composition, with each ingredient weighed and added to the media during preparation; eg. minimal agar
Bacterium must have what to grow?
carbon, energy, nitrogen, minerals, vitamins, growth factors, and water
microbes that obtain carbon from organic compounds such as carbohydrates and proteins
is required to assemble the raw materials found in the media and the biomolecues needed for continued cell growth
derive energy from the breakdown of organic molecules by fermentation or respiration (most bacteria and humans fall in this category)
rely on inorganic ions as an energy source, oxidizing inorganic substrates such as sulfur or iron to obtain energy
use photosynthesis pigments to convert sunlight into chemical energy through the process of photosynthesis
use light as a source of energy, but carbon is obtained from the breaking down of organic molecules such as glutamate
is essential for the synthesis of amino acids, nucleotides, and a few other cellular constituents
Minerals commonly required for bacterial metabolism include:
sodium, potassium, calcium, magnesium, manganese, iron, zinc, copper cobalt, and phosphorous
Two genera that is unable to synthesize all the vitamins on their own:
(so they need vitamins added in media in able to grow)
complex organic compounds that are required for the growth of some fastidious organisms
What kind of water is used in preparing media?
distilled or deionized water as tap water often contains ions such as calcium or magnesium that can interfere with bacterial growth
contains one or more ingredients that inhibits the growth of most bacteria, allowing only a single group to grow
allows all species to grow, but the inclusion of a specific ingredient in the media results in some bacteria appearing different than others
referred to as broths, milks, or infusions. are, at their most basic, simply nutrients dissolved in water
has the same formula as the liquid media except that a solidifying agent is added so that the media is solid at temperatures used to incubate bacteria; eg. agar
Bacteria can be inoculated into melted agar at what temperature without killing the cells?
50 degree Celsius
Why is agar used over gelatin?
-gelatin liquidfy at room temperature
-very few bacteria can utilize agar as a nutrient
What do you use if the pH in a media is too low?
NaOH: 1N and 0.1 N solutions, to adjust the pH upward
Once media is prepared, it must be autoclaved immediately because:
bacteria in the water, on the inside walls of the tube, and in the dehydrated medium will soon begin to grow, destroying the medium
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