Lab 8: Culturing; Microbes of the Environment - Lab Quiz 2, 2-6 Agar Deep Stabs

What growth patterns on the agar deep stabs is this?

obligate (strict) aerobe

• requires O2 to survive

• only grows at the top of the tube

What growth patterns on the agar deep stabs is this?

Obligate (strict) anaerobe

• Only grown at the bottom

• O2 kills the cells

What growth patterns on the agar deep stabs is this?

facultative anaerobe

• dense at the top & sparse growth below

• Grows better with O2

What growth patterns on the agar deep stabs is this?

microaerophile

• grows best just under surface

• likes lower O2 concentration

What growth patterns on the agar deep stabs is this?

aerotolerant anaerobe

• always ignore O2

• Grows sparsely throughout

define aerotolerance

The ability or inability to live in the presence of O2 (oxygen).

When organisms float on top of the medium, they produce a _____

When organisms float on top of the medium, they produce a pellicle.

When organisms sink to the bottom, this is known as _____.

When organisms sink to the bottom, this is known as sediment.

Another term used describe cloudy growth is _____.

Another term used describe cloudy growth is turbid.

Clumps within a broth display ___ growth.

Clumps within a broth display flocculent growth.

What’s the difference between a friable slang and a spreading edge slant?

Friable slant: dry and crusty

Spreading edge slant: spread everywhere

Define aerotolerance and purpose of stab; why do we use a needle and not a loop?

Aerotolerance: An organism's ability or inability to grow in the presence of O2

Purpose of stab: Stabbing introduces bacteria deep into the medium to observe oxygen tolerance.

Needle Usage: Minimizes disruption, ensuring bacteria are deposited along the stab line. (using a loop would → disrupt the agar and introduce O2 into it)

Describe the O2 gradient found within the medium; how was the gradient created?

Highest O2 concentration at the top, decreasing towards the bottom.

Created by autoclaving, which removes O2. During cooling (recheck), O2 diffuses back in, forming an O2 gradient.

How could you determine motility? (tell the difference between motile and non-motile bacteria)

Motile: If the organism spreads from the stab line, it’s motile.

Non-motile: growth remains on the stab line and does not spread

Review purpose and proper steps for quadrant streak method; pure vs. mixed cultures

Purpose: the streak method helps separate species from a mixed culture in order to isolate individual bacterial colonies from a mixed sample. → to obtain a pure culture by reducing bacterial density across quadrants.

The streak method of isolation: when a mixed culture is streaked over the surface of a plated agar medium. While you‘re streaking it: the cell density decreases → which leads to individual cells being isolated (these isolated cells grow into colonies consisting of only the original cell type, aka individual bacterial colonies)

Different types of streaking patterns:

Quadrant streak: used for samples with high cell densities

Simple zigzag: used for samples with lower cell densities

Steps for quadrant streak method

Before performing steps on the image:

1. Heat fix loop

2. Place the plate lid down on the table

3. Remove the base and hold it in the air at an angle (to avoid airborne contaminants from entering)

4. Then follow lab manual picture steps

1. What is Phenylethyl Alcohol Agar (PEA)?

2. How does it inhibit Gram-negative - bacteria?

(4-1 PEA)

1. A selective medium where only Gram-positive + bacteria grows on

2.