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Antimicrobials
cmpds that kill or inhibit microorgs
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Antibiotics
antimicrobials produced by microorgs that kill or inhibit the growth of other microbes
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Narrow spectrum antibiotic
specific for one bacterial strain
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broad-spectrum antibiotic
effective against a wide range of bacteria (G-neg and G-pos)
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Disinfectant
germicides (lethal to pathogens) for floors, workbenches, etc
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Antiseptics
inhibit microbial growth or kill microorgs; can be used on living tissue
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Phenol Coefficient
number on label, indicates killing power of disinfectant
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Bacteriostatic
only inhibits growth; does not kill bacterial cells
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Phenol Red Broth
Tests for carbohydrate fermentation (ie glucose, dextrose, lactose, sucrose
pos result = acid produced; red changes to Yellow color, possibly gas produced
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Methyl Red Test
tests ability of bact to metab glucose to produce acids
- Pos test = Red color
- Neg test = orange/yellow
E. coli is pos
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Voges-Proskauer test
Test if 2,3-butanediol is produced
add Barritt's reagent
Pos test = reddish color
E. coli is pos
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Citrate Test
Test if bact can use citrate to form oxaloacetate & pyruvate
pos test = color change from green to BLUE means bact using citrate
E. aerogenes is pos
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Oxidase Test
tests for cytochrome oxidase
pos test = color change from yellow to purple in presence of cyt ox
P. aeruginosa is pos
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Catalase Test
tests for catalase enzyme
hydrogen peroxide (as by-product of respiration) broken down by catalase; releases water & oxygen
Pos test = O2 bubbles
P. aeruginosa is pos
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Starch Hydrolysis
tests for production of amylase
starch agar is differential medium - tests ability of orgnsm to produce amylase, which hydrolyzes starch
add iodine to plate; iodine turns dark in presence of starch
pos test = clearing around bacterial growth means org hydrolyzed starch
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Urea Hydrolysis
Tests for Urease production
urease brks down urea to ammonia and CO2, causes change in pH
Pos test = color change from yellow to HOT PINK
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Nitrate Reduction
Testing for Nitrate Reductase production (reduces nitrate to nitrite)
add chem to react w/nitrate and pH indicator
Pos test = red; nitrate is being reduced to nitrite
- if not red, add zinc
- Red = nitrate reduction
- no color change = no nitrate reduction
E. coli is pos
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Selective Media
allows growth of certain types of orgs while inhibiting the growth of others
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Differential Media
Allows to distinguish between or among diff microorgs based on diff in colony appearance
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Mannitol Salt Agar (MSA)
Selective and Differential media
Salt selects for G-pos bac and differentiates based on bact ability to ferment mannitol
pos test = Phenol Red turns to yellow when acid is produced (meaning mannitol is fermented)
if colony grows, is g-pos; if turns yellow, ferment mannitol
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Levine Eosin Methylene Blue Agar (EMB)
select for G-neg and differentiate based on ability to ferment lactose
pos test = lactose fermenters produce blue-black colonies; strong lac fermenters produce green metallic colonies
non-lac fermenters produce colorless or amber colonies
if nothing grows, is G-pos = neg test
- E. aerogenes was pink
- E. coli was green
- P. aeruginosa was colorless
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