Micro lab 2

start of class procedure take results from last week

results on 3-way Streak

• Result: cultural characteristics (what is the colony morphology for S. aureus?)

Cultural characteristics are used to describe

colony morphology

colony morphology

the visual appearance/overall shape of the bacterial colony on the
plate

How do we describe bacterial colonies using cultural characteristics?

1. Size

2. Pigmentation

3. Form-

4. Margin-

5. Elevation-

size

describes the relative size of the bacterial colony

• pinpoint

• small

• medium

• large

pigmentation

the color (if any) that the bacterial colony produces while growing on a
plate

Chromogenic bacteria produce
pigments that result in colored
colonies
◦ Most colonies are not chromogenic
and appear white, grey, tan

Form

describes the overall shape of the whole colony

• circular: smooth unbroken periphery

• irregular: non-uniform edge

• Rhizoid: root like

• Spindle: ovoid

Margin

describes the outer edge of the colony

• Entire – even
  ◦ Lobabte - irregular
  ◦ Undulate – wavy
  ◦ Erose – sawtooth-like
  ◦ Filamentous – fuzzy, thread-like

Elevation

describes the height of the colony when compared to the agar surface

Flat – no difference
◦ Raised – slightly above
◦ Convex – dome-like
◦ Pulvinate – convex
◦ Umbonate – convex portion on top

Pure vs. contaminated culture

If you have a pure culture, you should expect colonies to have the same morphology. Multiple different colony morphologies can indicate contamination.

mixed cultures

a sample that contains two or more different living microorganisms

Streak for isolation purpose?

separate a mixed culture into pure colonies using 2 diff techniques: a 3-way streak or spread plate

Common types of microbial symbiotic relationships

1. Mutualism: both organisms benefit

2. Commensalism: one benefits, the other is unaffected

3. Parasitism: one benefits while the other is harmed

The difference between general growth media vs. selective and differential growth media

1. General growth: A medium that allows many different types of microorganisms to grow, including many bacteria, fungi, and yeasts.

2. selective function: A growth medium that lets certain organisms grow while stopping others because of its ingredients.

2. Differential function: A medium that lets certain organisms grow and separates them into groups based on what they do, such as fermenting sugars. The groups are identified by a color change.

Mannitol Salt Agar (MSA). MSA is a type of

selective and differential growth medium

• Selective : Grows Halophilic ("salt-loving") bacteria, inhibits non-halophiles

• differential:

For those bacteria that DO grow, we can
visually determine if the microbe ferments
the carbohydrate called mannitol

Perform Experiment 5

Take a mixture of E. coli and S. aureus, use two different plating techniques to separate them, then compare the colonies to see which technique gives the best isolated pure cultures.

Perform Experiment 6

• Label one TSA (tryptic soy agar) plate and one MSA (Mannitol Salt Agar.) plate.

• Wet a sterile swab with sterile saline.

• Swab an environmental surface of your choice and record the surface.

• Crosshatch the TSA plate with the swab.

• Repeat on the MSA plate.

What are ur best defense against pathogens

skin and your natural microbiota

Virulence factors

are strain-level differences (meaning different genes) within a bacterial species that aid an organism in pathogenesis

Virulence factors are characteristics of a pathogen that aid in an organisms pathogenesis

Nosocomial Infections

• An infection that is acquired in a hospital or other health care facility