Micro Lab Practical 2

What is the color of Gram-positive cells

purple

What is the color of Gram-negative cells

red/pink

You are Gram staining a known sample that contains both gram-positive and gram-negative bacteria. After you complete the staining, you realize that you performed the decolorizer step for 10 minutes instead of 10 seconds! Which of the following statements would correctly explain what you see?

Gram-positive organisms might incorrectly stain red

You are Gram staining a known sample that contains both gram-positive and gram-negative bacteria. After you complete the staining, you realize that you did not use the alcohol bottle at all. Which cells would appear purple?

Gram-positive cells

Gram-negative cells

Understanding the function of the tests is more important than identifying the bacteria correctly.

True

The FTM media tells us

the oxygen requirement of the bacteria

Aerobes

require oxygen to grow

Strict Anaerobes

grow only in the absence of oxygen

Facultative anaerobes

can grow either with or without oxygen

Bacteriophage

a virus that infects bacterial cells

Virion

a single viral particle

Plaques

clearing of bacteria in a lawn due to lysis

Plaque Forming Units (PFUs)

determined by counting the number of plaques (holes) in the confluent lawn

Proteases

enzymes that degrade proteins

Gelatinase

breaks down the gelatin protein

Respiration

molecules get oxidized to form CO2 and water; ATP is generated as energy source through oxidative phosphorylation

Fermentation

molecules partially break down to alcohols and aldehydes; ATP is synthesized through substrate level phosphorylation

We know respiration has occurred if:

the catalase test produces bubbles

We know fermentation has occured if:

acids are produced in the methyl red test.

Gelitinase anabolizes gelatin.

False

Staph aureus is an opportunistic pathogen.

True

We will know our bacteria is capable of hydrolyzing fat if _____ activity is detected.

Lipase

A positive Urea Test will appear pink

True

____ is the chemical we detect to indicate tryptophanase activity.

tryptophanase

UV light can be germicidal.

True

The SM110 plate tells us:

Colony pigment

S.aureus is a halophile

True

The MSA plate tests for

fermentation of mannitol

Most bacteria are:

mesophiles

An example of an antiseptic is:

rubbing alcohol

Bleach is a disinfectant

True

S. thermophiles is active in the refrigerator.

False

Making yogurt is a form of milk preservation

True

What are the 2 main functions of a capsule?

Protection and attachment

What color does FTM (Fluid Thioglycolate Medium) turn if oxygen is present?

Pink

What are the results of a positive glucose fermentation test?

the medium in the tube will turn yellow and gas bubbles will be present

What are the results of a negative glucose fermentation test?

the medium in the tube’s color will not change and no gas bubbles are present

What are the results of a positive lactose fermentation test?

Color change (acid production)

What are the results of a positive mannitol fermentation test?

the broth would turn yellow

What are the results of a positive oxidase test?

the cotton swab turning from yellow to purple in 10-30 seconds

What are the results of a negative oxidase test?

any change over 30 seconds

What are the results of a positive catalase test?

bubbles would appear and the production of oxygen gas would be present

What are the results of a positive nitrate test?

the broth would turn dark red

Is this a positive or negative indole test?

Positive

Which one is a positive methyl red test and which one is negative?

Left is positive, right is negative

Which result is positive and which one is a negative voges-proskauer test?

left is negative, right is positive

Which result is positive and which one is a negative citrate test?

left is negative and right is positive

Which result is positive and which one is a negative starch hydrolysis test?

left is positive, right is negative

Which result is positive and which one is a negative lipid hydrolysis test?

Left is positive, right is negative

Which result is positive and which one is a negative urea hydrolysis test?

pink is positive, orange is negative

Explain the results of Kligler’s iron agar is a multiple test medium

gas is produced if there are cracks in the medium

lactose fermentation results in the slant turning yellow

hydrogen sulfide production is identified by the butt turning black

the slant turns pink/red when lactose non-fermenters are present (salmonella)

How do you know if blood agar has completed lysis?

the medium turns clear

Gram stain examples

crystal violet, grams iodine, decolorizer, safranin

S.aures

gram positive

cocci

yellow color

P.vulgaris

gram-negative

motile

rod-shaped

grey color

P.aeroginosa

gram negative

rod-shaped

green color

E.coli

white color

gram negative

rod-shaped

found in intestines

Capsule Stains

Crystal Violet

Copper Sulfate