lab #4 2-3

What are agar slants primarily used for?

Cultivation and maintenance of stock cultures.

Why are growth characteristics on agar slants less diagnostically useful than colony morphology on agar plates?

Slants provide less opportunity to observe detailed colony characteristics such as size and shape.

What is filiform growth on an agar slant?

Dense, opaque, smooth, even growth with a smooth edge.

What is friable growth?

Dry, rough, crusty growth.

What is effuse growth?

Growth that spreads outward over the surface of the agar.

What is echinulate growth?

Growth with a spiny or pointed edge.

What is rhizoid growth?

Branched growth resembling roots.

What optical properties can describe growth on agar slants?

Opaque or translucent.

What does opaque growth mean?

Light cannot easily pass through the growth.

What does translucent growth mean?

Light can pass through the growth.

What characteristics can be used to describe growth on agar slants?

Margin, texture, optical properties, and color.

What are examples of slant growth margins?

Smooth, lobed, spreading/effuse, filamentous, rhizoid, and echinulate.

Why can the margin of growth on a slant be difficult to evaluate?

The slant may not be streaked in a straight line, or growth may cover the entire slant and reach the glass.

Can color be used to describe growth on agar slants?

Yes. Color is a variable characteristic of growth on slants.

What does Figure 2.31 demonstrate?

Different growth patterns on slants, including filiform, friable, effuse, echinulate, and rhizoid growth.

What does Figure 2.32 demonstrate?

Pigment production by different bacteria growing on slants.

Which organism in Figure 2.32 produces green pigment?

Pseudomonas aeruginosa.

Which organism in Figure 2.32 produces violet pigment?

Chromobacterium violaceum.

Which organism in Figure 2.32 produces red/orange pigment?

Serratia marcescens.

Which organism in Figure 2.32 produces rose-colored pigment?

Kocuria rosea.

Which organism in Figure 2.32 produces yellow pigment?

Micrococcus luteus.

What color does Staphylococcus epidermidis produce in Figure 2.32?

White.

What two environmental factors are specifically noted as influencing bacterial growth patterns?

Incubation time and temperature.

Can temperature affect pigment production?

Yes. Temperature can cause an organism to produce pigment at one temperature but not another.

What organism is used in Figure 2.33 to demonstrate the effect of temperature on pigment production?

Serratia marcescens.

What temperatures were used in Figure 2.33 to examine pigment production by Serratia marcescens?

25°C, 30°C, 33°C, 35°C, and 37°C.

What important point does Figure 2.33 demonstrate?

Even a small temperature difference, such as 2°C, can determine whether Serratia marcescens produces visible pigment.

Why can growth patterns on slants still be useful for identification?

Bacterial genera, and often individual species, can have characteristic growth patterns that provide useful identification information.

What organisms are recommended for observing growth patterns on slants in Exercise 2-3?

Bacillus subtilis, Corynebacterium xerosis, Kocuria rosea, Lactobacillus plantarum, Lactobacillus acidophilus, and Micrococcus luteus; Mycobacterium smegmatis and Proteus mirabilis are optional.

What should be used for comparison when growth is difficult to see on a slant?

An uninoculated tube of the same medium.

What should be recorded when examining the slants?

The growth pattern, including margin, texture, and color, plus a sketch of a representative portion.

What additional incubation information should be recorded with slant observations?

Incubation time, temperature, and the medium used.

What does pigmented mean when describing microbial growth?

The organism produces colored growth.

What does spreading edge mean?

Growth appears to radiate outward from the inoculated area.

What does transparent mean in the slant growth descriptions?

The growth is almost invisible or allows light to pass through.

What does friable mean?

The growth has a rough, crusty appearance.

What does filiform mean?

Smooth, even growth with a solid edge.

Why are agar slants better suited than agar plates for maintaining stock cultures?

Slants are practical for maintaining cultures because they require less surface area and are easier to store and handle over time.

What is the main purpose of Exercise 2-3?

To observe and describe the different growth patterns produced by bacteria on agar slants and compare them with growth on agar plates.