lab #4 2-4

What are growth patterns in broth useful for?

They can provide useful information when attempting to identify bacteria because bacterial genera and often individual species have characteristic broth growth patterns.

What is uniform fine turbidity (UFT)?

Growth that makes the broth evenly cloudy throughout.

What is flocculent growth?

Growth that appears as suspended chunks or pieces in the broth.

What is a pellicle?

A membrane or film of microbial growth floating at the surface of the broth.

What is sediment?

Microbial growth that collects at the bottom of the broth.

What is a ring in broth growth?

Growth concentrated around the top edge of the broth.

What are the 5 growth patterns you should recognize in this exercise?

Uniform fine turbidity, flocculent growth, pellicle, sediment, and ring growth.

Where does a pellicle form?

At the surface of the broth.

Where does sediment form?

At the bottom of the broth.

Where does ring growth occur?

At the top around the edge of the broth.

What does uniform fine turbidity look like?

The entire broth appears evenly cloudy.

What does flocculent growth look like?

Suspended flakes, chunks, or pieces throughout the broth.

What medium is shown in Figure 2.34 for comparing broth growth patterns?

Trypticase soy broth (TSB).

What organism is shown producing red pigmentation in Figure 2.35?

Rhodospirillum rubrum.

What causes the red color of Rhodospirillum rubrum?

Carotenoid pigments.

Under what conditions does Rhodospirillum rubrum grow as a photoheterotroph?

In the presence of light and absence of oxygen.

What should be used as a comparison when examining broth growth?

An uninoculated broth control.

Why is an uninoculated control important?

It provides a baseline so changes caused by microbial growth can be distinguished from the normal appearance of the medium.

What should be recorded when examining broth cultures?

The growth pattern, a sketch, and incubation conditions such as time, temperature, and medium.

What organisms are recommended for Exercise 2-4?

Bacillus subtilis, Corynebacterium xerosis, Kocuria rosea, Lactobacillus plantarum, Lactobacillus acidophilus, and Micrococcus luteus. Optional organisms include Mycobacterium smegmatis and Proteus mirabilis.

Why can broth growth patterns help identify an organism?

Different organisms can produce characteristic patterns of growth in broth.

What does pigmentation indicate in broth cultures?

Some organisms produce pigments that give the broth a characteristic color.

What is the difference between sediment and a pellicle?

Sediment collects at the bottom, while a pellicle forms a membrane at the surface.

What is the difference between a ring and a pellicle?

A ring is concentrated around the upper edge of the broth, while a pellicle forms a membrane across the surface.

What is the difference between uniform fine turbidity and flocculent growth?

Uniform fine turbidity makes the broth evenly cloudy; flocculent growth produces visible suspended chunks or flakes.

What is the main purpose of Exercise 2-4?

To examine the growth characteristics of different bacteria in broth and use those patterns as information for microbial identification.