Micro Lab

juniperk's version from 2017-07-24 17:03


Question Answer
Define a microbial culturea population of microbes that are growing in or on a medium.
Define a mediumsomething that contains nutrients for growth of the microbes & some of which provide information about chemical reactions that microbes carry out.
Define a microbial colonya group of microbes growing on a solid medium, all of the microbes in the colony having divided from a single parent cell, they are all identical & represent a pure culture.
Define a mixed culturecontains two or more species of microbes.
Define a pure culturecontains only one species of microorganism.
Define a stock culturewhere the identity of the microbes growing in the culture is known, they can be mixed or pure cultures.
Define Differential mediumallow separation of microbes based upon metabolic activity. Many contain dyes that are pH sensitive, changing colors when acids or bases are by products of metabolic activity.
Define selective mediumallows the growth of certain kinds of bacteria while inhibiting the growth of others.
How do you calculate total magnification?determined by multiplying the eye piece power (usually 10x) by the objective lens in place. EX. a 10x eyepiece and a 4x objective yields a total magnification of 40x
Define Bacteriostaticresults in the growth to stop; but does NOT kill. This type of chemical control of microbial growth can give our immune system time to catch up.
Define Bactericidalresults in microbial death.
Define Antibioticdrugs that are generally taken internally to control infections inside the body. A chemical that is produced naturally by a microorganism that inhibits growth of other microbes.
Define Antisepticchemicals that are used on living tissues to reduce the total number of microbes & prevent the growth of pathogens
Define Sterilizationcomplete lack of microbes; at best, disinfectants & antiseptics can reduce microbial counts to relatively safe levels.
Define Disinfectioncleaner for inanimate objects, such as kitchen surfaces or medical equipment. Does not kill endospores completely.
What is Skim milk agar used to test for?tests for the presence of the exoenzyme caseinase. Differential test A clearing around the streak of growth indicates a positive result. If the area surrounding the growth remains cloudy, the organism cannot break down casein, & is a negative result.
What is SIM tube used to test for?tests for sulfur reduction ...thiosulfate reductase can reduce sulfur to hydrogen sulfide gas ( black precipitate = positive), indole production... enzym tryptophanase will degrade tryptophan into indole, pyruvate and ammonia (kovac reagent is added= red ring positive), & motility (positive = growth from stab line). Differential test
What are Durham tubes used to test for? And what are their purpose? tests for gas production. The inverted test tube traps gas bubbles produced during sugar fermentation. Also used in Nitrate Broth test and a bubble indicates the organism reduced nitrate to nitrogen gas and is positive.
What is Blood agar used to test for? test distinguishes bacteria based in their ability to lyse red blood cells. Differential test
What is Simmons citrate agar used to test for? tests for the production of the enzyme citrase. Differential
What does Thioglycollate broth test for?test for bacteria based on oxygen requirements. It contains an indicator called methylene blue that is a blue-green in the presence of oxygen & colorless in an anaerobic environment. Differential
In a Thioglycollate broth how can you tell if an organism is an obligate aerobe, obligate anaerobe, or facultative anaerobe?obligate aerobes will only grow in the oxygen rich top layer. Require oxygen to grow obligate anaerobes will only in the lower areas of the tube. Oxygen is toxic to these organisms. facultative anaerobes can grow throughout the medium but will primarily grow in the middle of the tube. Can grow with or without oxygen.
What does Mannitol salt agar [MSA] test for?tests for halophiles based on the ability to ferment mannitol. MSA has a high salt content & has a pH indicator that turns the agar yellow if the acidic by products of mannitol fermentation are present. Differential & Selective
What does Nitrate broth test for?tests for nitrate reductase that anaerobically [without oxygen] reduce nitrate. During the nitrate reduction process, nitrate is reduced to nitrite, which can then be reduced to ammonia, & finally to nitrogen gas. Differential
What does Starch agar test for?tests for the presence of the exoenzyme amylase that hydrolyzes the polysaccharide starch allowing the glucose subunits to enter the cell. Differential Brown plate- with clearing = positive.
What does GELATIN test for? GELATIN tests for the presence of the exoenzyme gelatinase. Gelatinase hydrolyzes the large protein molecule, gelatin, into polypeptides, peptides & amino acids that enter the cell for metabolic use. Differential
What do SUGAR FERMENTATION TUBES test for?tests for sugar fermentation. Consists of Glucose, Lactose, & Mannitol. RED tube = negative Durham tubes are also used to test for gas. Differential
What are the steps of a SMEAR PREP? Remove a clean glass slide from the box, apply a small drop of water to the middle of the slide with a sterile loop, using aseptic technique--- use the inoculating loop to get a small sample from the broth or agar and spread across slide with water droplet. Let the slide air dry then apply clothespin to one end and heat fix the sample over the outside of the incinerator for about 20 seconds. Let the slide cool before proceeding with next steps.
What are the steps involved in a SIMPLE STAIN?steps after a sample has been spread out on a slide. Let the sample air dry Heat fix the specimen to the slide by clipping the clothespin to one end of the slide & passing over the incinerator. Allow the slide to cool for several seconds then, using the clothespin place the slide on the rack over the dishpan, cover the specimen with a puddle of crystal violet; allow the dye to sit on the slide for 1 minute
What are the steps involved in a GRAM STAIN?steps start the same as the smear prep process. However after Letting crystal violet [the primary stain] sit for 60 seconds; rinse with distilled water Then cover the smears with iodine [the mordant] & allow to sit for 60 seconds; then rinse with distilled water Destain with decolorizer [alcohol] for a quick 10 seconds; then immediately rinse with distilled water Last step is to cover the smears with safranin [the counterstain] & allow it to sit for 30 seconds; then rinse with distilled water Then wipe the bottom of the slide & dab the top to dry.
What are the steps involved in an ENDOSPORE STAIN?steps are After air drying & heat fixing. Using the fume hood, place slide on rack over the wok, flood the sample with malachite green. Let the malachite green sit on the slide for 5 minutes, adding more stain as needed to keep the sample saturated. You'll discard excess stain on the slide in the wok before going back to lab table. Then gently rinse with distilled water. Flood the sample with safranin allow the stain to remain on the slide for 60 seconds; then gently rinse with distilled water. Wipe the bottom of the slide & dab the top to dry. Spores will appear green & vegetative cells will be red or pink. These can be hard to stain because endospores are known to have tough coat.
Why is a DILUTION SERIES often done before making colony counts?If the bacteria are spread out enough, each bacterial cell in the original sample should produce a single colony. Usually, bacterial samples must be diluted considerably to obtain reasonable counts.
What is the purpose for performing a STREAK FOR ISOLATION procedure?obtain a pure culture by reducing the number of microbes on the plate so individual parent cells are spaced widely enough apart to grow into well separated colonies.
What is the KIRBY-BAUER DISK DIFFUSION METHOD? What is the zone of inhibition?test the effectiveness of antimicrobial chemicals by measuring how well they inhibit the growth of microbes on an agar plate. The ZONE OF INHIBITION is the varying degrees of the inhibited growth of microbes around the disks. The bigger the zone of inhibition the better the ability to kill.
For what reasons might a chemical that is usually thought to be a good antimicrobial show no zone of inhibition?-No chemical is 100% effective on every microbe -One chemical might kill a specific type of microbe very well but It may not even touch a different type of microbe
How would you test for the ability of a microbe to produce catalase?Perform a catalase test. Catalase degrades hydrogen peroxide into water and molecular oxygen. Place a drop of H2O2 on microscope slide and add some fresh growth from an agar plate. Positive result the bubbles are present. Negative result NO bubbles are present.
Why is a Blood Agar test important in a clinical lab?Differentiates between pathogenic and nonpathogenic species -pathogenic are hemolytic; meaning they CAN lyse RBC's -nonpathogenic are not hemolytic; meaning they can NOT lyse RBC's This is important in a clinical lab to identify the pathogenic microbe for treatment.
What are ACIDIC DYES? Explain the general use of this dye on bacteria.Bacteria cant be stained by ACIDIC DYES because these dyes have anionic [negatively charged] chromosphores [color bearing ions]; which is repelled by the cells; since bacteria is also negatively charged. These dyes can be used for capsule staining.
What are BASIC DYES? Explain the general use of this dye on bacteria.Knowing that bacteria is negatively charged, the dyes commonly used in labs are BASIC DYES. These are cationic dyes [positively charged] making them attracted to the cells; they include dyes such as methylene blue & crystal violet.
Trypanosoma What type of human sample is viewed to diagnose this infection?Blood
Define bacteriophagea virus that infect & eventually causes lysis of bacterial cells.
Define VIRAL PLAQUEonce a bacterial cell is infected with a viral particle, then the virus is replicated. Eventually host cell bursts causing the release of hundreds of viral particles that go on to infect adjacent bacterial cells, as this proceeds, a visible blank spot in the bacterial lawn appears which is called the viral plaque.
What is a plasmid and how can it be inserted into a bacterium? What is this process called?Bacterial DNA exists in the nucleiod as a single circular chromosome & throughout the cytoplasm as small extra-chromosomal DNA called PLASMIDS. Bacteria transfer plasmids from one to the next, sharing genes among one another, & adapting to new environments. The ability of bacteria's ability to replicate these plasmids is during binary fission & is the basis of genetic transformation. The plasmids are used as vectors to bring DNA of interest into the cell where it can integrate into the genome & can be translated into proteins not normally found in that organism.
How does UV light affect bacterial cells and bacterial endospores?affects microbial growth by damaging DNA & preventing normal replication of genetic material in cells.
What is the significance of biochemical tests in the identification of microorganisms?Physiological reactions to nutrients as evidence of the absence or presence of enzymes [second part of unknowns lab testing, Bio testing with the tubes] These tests Identify the properties of the organism and helps to differentiate what organism it is.
Why does BACTERIOPHAGE have to be grown in bacteria?BACTERIOPHAGE has to be grown in bacteria, because bacteriophage is a virus & viruses are not living & cannot reproduce or grow without a host cell.

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