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Laboratory tests
the different tests/media to determine the bacterial species
47
Microbiology
Undergraduate 2
11/15/2011

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Term
Mixed culture
Definition
Culture of bacteria where more than one species of bacteria is present.
Term
Pure Culture
Definition
A bacterial culture with only one species present
Term
Streak plate
Definition
An agar plate where the bacteria is spread over from another source (culture or environment)
Term
Quadrant streak
Definition
Each sector is more diluted than the last, one line is dragged from the previous squiggle to make a new squiggle.
Term
Ubiquitous
Definition
Grows anywhere/isn't hard to grow
Term
Opportunistic Pathogens
Definition
They are not pathogenic normally but if introduced into a host where the conditions are suitable for growth they could become pathogenic.
Term
Fastidious
Definition
Picky: the bacteria need their food to be in the form they use internally already in the environment.
Term
Nonfastidious
Definition
The food they find can be in a different form than they need internally.
Term
Undefined medium
Definition
The exact components and amounts are unknown eg: beef broth
Term
Defined medium
Definition
Where all the exact chemical components and amounts are known.
Term
Aerotolerance
Definition
The oxygen needs of the bacteria.
Term
Auto-claving tube media
Definition
When this is done the free oxygen in the medium for the most part is removed. When the tube is removed from auto-clave the oxygen is reintroduced but only to the top layers. This forms oxic zones.
Term
Capnofiles
Definition
Bacteria that survive only when there are high levels of CO2
Term
Fluid Thioglycollate medium
Definition
Used to grow anaerobic and microaerophilic bacteria. The bacteria is grown in this medium to determine its aerotolerance.
Term
Cardinal temperatures
Definition
Three points: minimum temp, maximum temp, and finally optimum temp to grow in.
Term
Psychrophile
Definition
Bacteria that survive only below 20 degrees celcius
Term
Mesophile
Definition
Bacteria grown between 15 and 45 degrees celcius, ambient temperatures usually and many are pathogens (since they can live in us).
Term
Thermophile
Definition
Bacteria that need higher temperatures (40-60 degrees celcius) to survive.
Term
Hyperthermophile
Definition
Bacteria survive only in much higher temperatures of 65-115 degrees celcius.
Term
Acidophile
Definition
Bacteria that live in pH below 5.5 or highly acidic environments
Term
Nuetrophile
Definition
Bacteria that live in relatively neutral pH between 5.5 and 8.5
Term
Alkaliphile
Definition
BActeria that grow in basic environments, above pH 8.5
Term
Basic stains
Definition
These are alkaline stains that are simple stains normally. They stain the inside of the cell because the alkaline chemical becomes positive and is attracted to the negative cell surface of (most) bacterial cells.
Term
Chromogen
Definition
The colored molecule of the stain.
Term
Chromophore
Definition
The component of the chromogen that gives the compound its color, there can be more than one color so more than one chromophore.
Term
Auxochrome
Definition
The charged portion of the chromogen that will bind chemically to act as a dye.
Term
Negative stains
Definition
These stains are acidic and so they are negative, this means the chromogen of these stains will repel the bacterial cell surface. The area around the cell is stained as a result.
Term
Gram Stain
Definition
This is a differential stain that is based on cell wall differences in bacteria. they can be gram positive or negative.
Term
Gram Positive bacteria
Definition
They appear purple under the gram stain. This is because they resisted decolorization of the primary stain. Their cell wall is made up of multiple layers of peptidoglycan.
Term
Gram negative bacteria
Definition
These show up as pink in the gram stain because the cell could not resist decolorization of the primary stain. The cell wall is made of two layers (lipid and peptidoglycan) the lipid layers is broken down and the peptidoglycan is porous enough to allow the primary stain to leave the cell.
Term
Capsule Stain
Definition
The capsule itself can't be stained but the area around it and the cell itself can be. If a space between the two stains appears then the bacteria have capsules.
Term
Endospore stain
Definition
The endospore resists staining (because of the keratin in it) and so the color must be forced inside, in our case with steam/heat. The mother spore cell is stripped of color and counter-stained differently.
Term
Central endospore
Definition
The endospore is found in the middle of the mother spore cell.
Term
Terminal endospore
Definition
The endospore in found at the far side of the mother spore cell. the endospore is just on the edge.
Term
Subterminal endospre
Definition
The endospore is positioned between the terminal and central locations.
Term
Manitol Salt Agar
Definition
This is a differential medium that selects for gram positive bacteria. There is a phenol red indicator in the medium that turns yellow in acidic conditions (fermentation) and pink in alkaline. The High NaCl concentration inhibits gram negative bacteria. Staphylococcus bacteria grow on the agar, staphylococcus aureus turns yellow.
Term
Phenyl ethyl Alcohol Agar
Definition
This inhibits the growth of Gram negative bacteria. This is because the alcohol interferes with DNA synthesis. Gram positive bacteria that will grow on this medium are: staphylococcus, streptococcus, lactococcus, and enterococcus.
Term
Eosin Methylene Blue Agar
Definition
This will inhibit the growth of gram positive bacteria. Eosin Y and methylene blue are both dyes that inhibit gram positives. This medium indicates for fermenters and coliforms. pink/mucoid=fermentation, little acid, possible coliform. purple/black, maybe metallic green= fermentation, acid production, probable coliform. Colorless=no fermentation, not a coliform.
Term
Hektoen Enteric Agar
Definition
This is a differential medium that is selective for gram negative bacteria and separates between salmonella and shigella (even proteus). The medium indicates for sulfur reduction (black precipitate where there is H2S gas, because the gas reacts with the iron. Also fermentation, the color changes to either yellow or pink.
Term
MacConkey Agar
Definition
This is selective for gram negative bacteria, the bile and crystal violet dyes together inhibit all gram positive bacteria. (crystal violet inhibits enterococcus and staphylococcus. Neutral red dye indicates for the presence of acids=turns pink when fermentation occurs. If there is fermentation the bacteria are likely coliforms.
Term
Phenol red broth
Definition
This is a fermentation test, the substrate can change though. The phenol red indicates for pH, yellow color change= acid production, fermentation. Pink color change=degradation of peptone so alkaline broth. There is an inverted tube inserted to collect any gas.
Term
Catalase test
Definition
When organisms are aerobic they use oxygen in their electron transport chain as the final electron acceptor. H2O2 is produced and catalase is produced to breakdown this harmful by-product. If the catalase does come into contact with H2O2 then bubbles are formed.
Term
Citrate Test
Definition
This is a utilization medium where the only source of carbon is sodium citrate, the only source of nitrogen is ammonium phosphate. If the citrate is utilized by the bacteria the bromothymol blue in the agar goes from green to blue bacause the ammonia produced from ammonium phosphate decomposition makes the medium alkaline (ammonium hydroxide is also produced). Only Enterobacteria (gram negative group) will use citrate.
Term
Starch Hydrolysis test
Definition
The agar has starch as the main nutrient, this is too large of a molecule to enter the cell directly. The bacteria that use it will excrete amylase to break down the starch extracellularly then take in the smaller sugars. Once the bacteria has grown in the agar iodine solution is added. If there is starch the iodine stains it black/brown. Where the bacteria has used the starch there will be a clear area around the growth. This is to separate enterococcus bacteria from other gram positives.
Term
Casein Hydrolysis test
Definition
This test is to see if the bacteria produce casease to break down casein. If the bacteria has casein then a clearing will show up around the bacteria.
Term
Casein Hydrolysis test
Definition
This test is to see if the bacteria produce casease to break down casein. If the bacteria has casein then a clearing will show up around the bacteria.
Term
Sim medium
Definition
This medium conducts many tests at once. The agar is in a tube and the inoculation is done by stabbing the agar. If the bacteria grow anywhere other than the stab line the bacteria are motile. The medium has iron that reacts with H2S gas from sulfur reducing bacteria to form a black precipitate. Kovac's reagent can be added to test for indole (a by-product of tryptophan breaking down through tryptonase action)the medium turns red if there was tryptonase.
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