microbio lab unit exam 2

Identify PEA

Identify MSA

Identify EMB

Identify MAC

Identify BAP

What is PEA selective for?

gram positive bacteria

What is PEA differential for?

PEA isn’t differential

What is MSA selective for?

salt-tolerant bacteria

What is MSA differential for?

mannitol fermentation

What is EMB selective for?

gram negative bacteria

What is EMB differential for?

lactose fermentation (EMB)

What is MAC selective for?

most gram negative bacteria - MAC

What is MAC differential for?

lactose fermentation

What is BAP selective for?

not selective

What is BAP differential for?

hemolysis type (alpha, beta, gamma)

What chemicals contribute to PEA’s selectivity?

phenylethyl alcohol

What chemicals contribute to MSA’s selectivity?

NaCl 7.5%

What chemicals contribute to EMB’s selectivity?

eosin and methylene blue

What chemicals contribute to MAC’s selectivity?

crystal violet and bile

Name of pH indicator - MSA

phenol red (MSA)

Name of pH indicator - MAC

neutral red

What does positive and negative differential reactions look like for MSA?

positive:

• yellow with growth

negative:

• growth, but plate stays light red

What does positive and negative differential reactions look like for EMB?

positive:

• dark purple colonies or metallic green growth

negative:

• uncolored/pink growth

What does positive and negative differential reactions look like for MAC?

positive:

• pink growth

negative:

• yellow/colorless growth

BAP - identify and describe alpha hemolysis

green/brown haze on medium around growth

BAP - identify and describe beta hemolysis

clear/translucent halo around growth on medium

BAP - identify and describe gamma hemolysis

no change to medium

Starch Hydrolysis - What enzyme are we looking for?

amylase

Starch Hydrolysis - What reagent was added to this test?

Gram’s iodine

Starch Hydrolysis - What does positive reaction look like?

growth remains amber colored

Starch Hydrolysis - What does negative reactions look like?

growth/agar will turn dark

Catalase - What enzyme are we looking for?

catalase

Catalase - What does positive reactions look like?

presence of bubbles

Catalase - What does negative reactions look like?

no bubbles

Catalase - What media can be used to perform?

uncolored solid media with no dyes and no BAP

Catalase - What reagents are used?

hydrogen peroxide

Catalase - What is the end product?

water and oxygen

Oxidase - What enzyme are we looking for?

cytochrome c oxidase

Oxidase - What does positive reactions look like?

blue color change within 30 seconds

Oxidase - What does negative reactions look like?

no color change or color change after 30 seconds

Oxidase - What media can be used to perform these test?

uncolored solid media with no dyes

Oxidase - What reagent is used?

oxidase reagent

Oxidase - What is the end product?

indophenol blue

Carbohydrate Fermentation - What is the pH indicator?

phenol red - carb fermentation

Carbohydrate Fermentation - How is gas captured?

with a Durham tube

Carbohydrate Fermentation - What does positive reaction look like?

yellow with no bubble ; yellow with bubble

Carbohydrate Fermentation - What does negative reactions look like?

fuchsia with growth; red with no growth observed

Carbohydrate Fermentation - How to record/format results?

• A (yellow w no bubble)

• G (yellow w bubble)

• K (fuchsia w growth)

• (-) (red w no growth)

Indole - What medium is used?

tryptone broth

Indole - What enzyme are we looking for?

tryptophanase

Indole - What is the end product?

red rosindole dye at the surface

Indole - What reagent is used?

Kovac’s reagent

Indole - What does the positive reaction look like?

vibrant red dye at the surface

Indole - What does the negative reaction look like?

yellow/gold color at the surface

MR - What is the medium used?

MR-VP broth

MR - What is the end product?

stable acids

MR - What does positive reactions look like?

red/pink color change

MR - What does negative reaction look like?

orange/yellow color change

MR - What is the pH indicator?

methyl red

VP - What medium is used?

MR-VP broth (VP)

VP - What is the end product?

acetoin

VP - What reagents are used?

VPA, VPB

VP - What does positive reactions look like?

red/pink color change that may take up to 30 minutes

VP - What does negative reactions look like?

remains yellow/amber colored

Citrate - What medium is used?

Simmons’ citrate slant

Citrate - What enzyme are we looking for?

citrase

Citrate - What is the end product?

alkaline products

Citrate - What does a positive reaction look like?

blue color change and growth observed

Citrate - What does the negative reaction look like?

green color change and no growth observed

Citrate - What is the pH indicator?

bromothymol blue

KIA - What’s the full name of the slant?

Kligler’s Iron Agar

KIA - What is the pH indicator?

phenol red

KIA - What is the H2S indicator?

break or lifting of the agar

KIA - What sugars are being tested?

glucose and lactose

KIA - Correctly report and interpret results.

(slant/b*tt ; lactose/glucose)

A/A, G, H2S

• ferments glucose and lactose, produces gas and H2S

K/A, no G, H2S

• ferments glucose only, doesn’t produce gas, produces H2S

A/A, G, no H2S

• ferments glucose and lactose, produces gas, doesn’t produce H2S

K/A, no G, no H2S

• ferments glucose, doesn’t produce gas or H2S

KIA - What are the end products?

sugar fermentation, gas production, H2S production

Gelatin Hydrolysis - What does the test look like?

Gelatin Hydrolysis - What medium is used?

TSB tube

Gelatin Hydrolysis - What does positive reactions look like?

the strip will have become translucent blue and you can see the medium thicken

Gelatin Hydrolysis - What does negative reactions look like?

the strip stays a dull olive color and medium is still very fluid

Urea Hydrolysis - What does the test look like?

Urea Hydrolysis - What are the end products?

ammonia

Urea Hydrolysis - What does positive reactions?

a red or fuchsia color change because of ammonia

Urea Hydrolysis - What does negative reactions look like?

another other results like orange, salmon, or yellow

LDC - What does this test look like?

LDC - What is the medium?

Moeller’s decarboxylase medium with lysine

LDC - What is the pH indicator?

bromocresol purple

LDC - What is the function of mineral oil?

to create an anaerobic environment in the tube that enhances lysine decarboxylase activity

LDC - What is the end product?

cadaverine

LDC - What does positive reactions look like?

appears purple

LDC - What does negative reactions look like?

appears yellow throughout

Nitrate Reduction - What reagents are used?

nitrate reagent A and nitrate reagent B

Nitrate Reduction - Correctly interpret results after each step.

after the broth has incubated, all reagent A and B to the tube and let it sit for 5 minutes, if after 5 minutes, the tube turned red, nitrite is present and the test is done.

if there was no color change after adding A and B, add a small amount of zinc powder and let sit for 5 minutes, if the tube turned red, nitrate reductase was not reduced so it would be negative but if the tube stayed clear, it is positive as it produces both nitrate reductase and nitrite reductase

Bacitracin - What’s susceptible or resistant?

susceptible

• > or = to 17mm

resistant

• < or = to 13mm

Novobiocin - Determine what’s susceptible or resistant.

susceptible

• > or = to 16mm

resistant

• < 16mm

Coagulase - What does the test look like?

Coagulase - What is the name of the medium?

rabbit plasma

Coagulase - What proteins are involved in the reaction?

fibrinogen

BAC - Determine susceptible or resistant

susceptible

• > 6mm

resistant

• < or = to 6mm

SXT - Determine susceptible or resistant

susceptible

• > or = to 16mm

resistant

• < or = to 10mm