Micro Lab Practical

cmpds that kill or inhibit microorgs

antimicrobials produced by microorgs that kill or inhibit the growth of other microbes

specific for one bacterial strain

effective against a wide range of bacteria (G-neg and G-pos)

germicides (lethal to pathogens) for floors, workbenches, etc

inhibit microbial growth or kill microorgs; can be used on living tissue

number on label, indicates killing power of disinfectant

only inhibits growth; does not kill bacterial cells

Tests for carbohydrate fermentation (ie glucose, dextrose, lactose, sucrose

pos result = acid produced; red changes to Yellow color, possibly gas produced

tests ability of bact to metab glucose to produce acids

• Pos test = Red color
• Neg test = orange/yellow

E. coli is pos

Test if 2,3-butanediol is produced

add Barritt's reagent

Pos test = reddish color

E. coli is pos

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

tests for cytochrome oxidase

pos test = color change from yellow to purple in presence of cyt ox

P. aeruginosa is pos

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

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

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

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

allows growth of certain types of orgs while inhibiting the growth of others

Allows to distinguish between or among diff microorgs based on diff in colony appearance

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

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