MICRO 020 Lab Practicum Exam Questions with Correct Answers Latest Update 2025/2026
MacConkey Agar (MAC) - Answers Inhibits G+, Selective for G-.
Contains CH2O lactose which differentiates G- bacteria on their activity of ferment lactose.
Organisms that ferment lactose, produces acid and products react with neutral red dye.
Ex. E aerogenes and E coli produce pink/purple colonies, they are able to ferment lactose in the
media
Eosin Methelyne Blue Agar (EMB) - Answers Contains eosin and blue dye. Inhibits G+, Selective
for G-.
Encourages growth of fecal coli forms.
Ex. E. aerogenes produces pink/purple colonies, able to ferment lactose in media.
Ex2. E coli is an acid producer, turns colonies green metallic.
Ex3. C freundii produces sheens.
Blood agar - Answers Gamma hemolysis= no lysis of rbc's; no change in media around colonies.
Alpha hemolysis: incomplete lysis of rbc's with greenish halo around colonies.
Beta hemolysis: complete lysis of rbc's; clear zone around colonies.
Ex. E aerogenes: large, smooth flat colonies with entire margin w/o beta hemolysis.
Ex2. E coli: greyish white moist colonies.
SIMS - Answers Tests for Sulfur reduction, Indole, and Motility.
Positive:
Sulfur: H2- blackening along stab line
Ex. C. freundii
Indole: has enzyme, tryptophanse.
Ex. E coli
Motility: Turbid throughout the tube.
Ex. All G-: E aerogenes, E coli, C fruendii
Durham tube fermentation - Answers Positive: Bacteria able to ferment glucose and lactose to
produce acid and gas turns yellow / bubbles.
MacConkey Agar (MAC) - Answers Inhibits G+, Selective for G-.
Contains CH2O lactose which differentiates G- bacteria on their activity of ferment lactose.
Organisms that ferment lactose, produces acid and products react with neutral red dye.
Ex. E aerogenes and E coli produce pink/purple colonies, they are able to ferment lactose in the
media
Eosin Methelyne Blue Agar (EMB) - Answers Contains eosin and blue dye. Inhibits G+, Selective
for G-.
Encourages growth of fecal coli forms.
Ex. E. aerogenes produces pink/purple colonies, able to ferment lactose in media.
Ex2. E coli is an acid producer, turns colonies green metallic.
Ex3. C freundii produces sheens.
Blood agar - Answers Gamma hemolysis= no lysis of rbc's; no change in media around colonies.
Alpha hemolysis: incomplete lysis of rbc's with greenish halo around colonies.
Beta hemolysis: complete lysis of rbc's; clear zone around colonies.
Ex. E aerogenes: large, smooth flat colonies with entire margin w/o beta hemolysis.
Ex2. E coli: greyish white moist colonies.
SIMS - Answers Tests for Sulfur reduction, Indole, and Motility.
Positive:
Sulfur: H2- blackening along stab line
Ex. C. freundii
Indole: has enzyme, tryptophanse.
Ex. E coli
Motility: Turbid throughout the tube.
Ex. All G-: E aerogenes, E coli, C fruendii
Durham tube fermentation - Answers Positive: Bacteria able to ferment glucose and lactose to
produce acid and gas turns yellow / bubbles.
