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Lab Quiz # 3 Review

Lab Ex.'s 11,12,13,14

QuestionAnswer
Contamination Presence of unwanted microbes
Streak Plate technique A loop is used to streak the mixed sample many times over the surface of a solid culture medium in a Petri plate.(process of streaking loop repeatedly over agar allows bacteria to fall off loop 1 by 1 each cell develops into colony). Most commonly used.
Spread Plate technique A small amount of previously diluted specimen is spread over the surface of a solid medium using a spreading rod.
Pour plate technique A small amount of diluted sample is mixed with melted agar and poured into empty, sterile Petri dishes. After incubation, bacterial growth is visible as colonies in and on the agar of a pour plate.
What is a contaminant? Biological, chemical, physical, or radiological substance (normally absent in the environment) which, in sufficient concentration, can adversely affect living organisms through air, water, soil, and/or food.
How would you determine whether a colony was a contaminant on a streak plate? The difference from majority of the colonies; growing off the streak live.
How would you determine whether a colony was a contaminant on a pour plate? It's hard to tell
What is the disadvantage of the streak plate technique? Of the pour plate technique? Both are dilution techniques, so only microorganisms in majority will be isolated. Streak plate allows observation of colony morphology and selected isolated colonies. Main advantage of pour plate is able to count # of bacteria.
Selective media Contain chemicals that prevent growth of unwanted bacteria without inhibiting growth of the desired organism.
Enrichment media Are usually liquid media, contain chemicals that enhance growth of desired bacteria. Other bacteria will grow, but the growth of desired bacteria will be increased.
Differential media These media contain various nutrients that allow the investigator to distinguish one bacterium from another by how they metabolize or change the media with a waste product.
How did the results observed on the mannitol salt an EMB correlate to the Gram reaction of the bacteria? Mannitol Salt > Gm (+)'s grow well. EMB > Gm(-)'s grow well.
Which medium is selective? EMB and Mannitol salt
What is the purpose of peptone in the media? For bacteria that cannot use the sugar in the agar.
What is the purpose of agar in the media? It's a solidifying agent.
What ingredient makes Mannitol salt selective? "High" (75%)of NaCl (7.5%)
What was the Growth on EMB? (+) was E.coli with a metallic green color and P. aeruginosa which was colorless. (-) With growth on mannitol salt agar was M. luteus with yellow colonies and Staph. epidermis which had white colonies.
Catabolism All decomposition reactions in a living organism; the breakdown of complex organic compounds into simpler ones.
Carbohydrates Are organic molecules that contain carbon, hydrogen, and oxygen in the ratio (CH20). Can be classifyied based on size: monosaccharides, oligosaccharides, diaccharides, and polysaccharides.
Monosaccharides Simple sugars containing from 3 to about 7 carbon atoms.
Oligosaccharides Composed of 2 to about 20 monosaccharides. Diasaccharides are the most common Oligosaccharides.
Polysaccharides Consist of 20 or more monosaccharide molecules.
Hydrolytic enzymes (Exoenzymes) that leave the cell and break down, by the addition of water, large substrates into smaller components which can then be transported int the cell.
Oxidative catabolism Requires the presence of molecular energy (oxygen). some bacteria using endoenzymes, catabolize glucose oxidatively, producing carbon dioxide.
Fermentative catabolism Does NOT require oxygen but may occur in the presence of oxygen presence.
OF medium A nutrient semisolid agar deep containing a high concentration of carbohydrates & low concentration of peptone. (The peptone will support the growth of bacteria that don't use carbohydrates. One tube open to air is used & one tube sealed to keep air out)
How can you tell amylase is an exoenzyme and not an endoenzyme? Starch is hydrolyzed outside a bacterial cell.
How can you tell from OF-glucose medium whether an organism uses glucose aerobically. Organisms produces acid in open tube ONLY when using glucose aerobically.
Fermentation tube Used to detect acid and gas production from carbohydrate. (Fermentation medium contains peptone, and acid-base indicator (phenol red), an inverted tube to trap gas, and 0.5-1.0% of the desired carbohydrate.
MRVP test Used to distinguish organisms that produce large amounts of acid from glucose and organisms that produce the neutral product acetonin. (MRVP medium is a glucose-supplemented nutrient broth used for the methyl red (MR)test and the Voges-Proskauer (V-P)test
Why are fermentation tubes evaluated at 24 and 48 hours? Within 24 hours check for growth, acid and gas production may be present. At 48 hours many bacteria may have began growing oxidatively on the peptone after exhausting the carbohydrate supplied, causing neutralization, turns red becuz ammonia production
Which of these medias is selective? Why is it selective? Citrate agar is selective. Because only bacteria that can use citrate as their sole carbon source and NH4+, Nitrogen can grow.
Could an organism be a fermenter and also be both MR and V-P negative? Explain. Yes, some fermentation could occur/produce excess neutral products other than acetonin, such as alcohol (ETOH).
Created by: KJones040607 on 2011-10-19



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