Mic 224

Introduction, Lab Safety Quiz,

And Environmental Plates

Microorganisms in the Environment

• Microbes are ubiquitous– From the Antarctic to Hydrothermal vents

• Found in either 2 stages of development– Active- water is available, organisms are

dividing– Dormant-spores

Tools of the Trade

• Petri Dishes-used to grow organisms of interest

• 3 parts: lid, bottom, media (located in bottom of dish)– Organisms must be transferred directly to the

media, NEVER TO THE LID

Petri Dish

Culture Media

• Contains nutrients organisms need to survive– Proteins, carbohydrates, vitamins, minerals,

water

• Media is available in two forms: broth or solid– Broth-liquid, usually in a test tube– Solid-deeps, slants, plates

• Solid media contains agar (the solidifying agent)– Normal concentration is 1.5% agar

Culture Media

• May be chemically defined or complex– Defined: one in which the exact chemical

composition is known – Complex: exact composition is not known:

contains products such as blood, etc

• Todays media: – Nutrient agar: general purpose-supports the

growth of a wide range of organisms– Potato Dextrose Agar: selective media-

selects for Fungi

Colony Morphology

• Colony- result of a single organism dividing into millions of organisms that become visible

• Colonial Morphology- consists of size-diameter of colony (mm); elevation-raised/lowered; margin (edge)-rough, variegated, etc; pigment-color; and texture-smooth, rough,etc

Colony Morphology

Size of Colony:

Colony Morphology

• Shape refers to the overall appearance of the colonies. The descriptors here are punctiform, circular, irregular, filamentous (has individual thin projections), or rhizoid (has thin, branching projections).

Colony Morphology

• Height/Elevation• The colony height, or elevation, is a description of how the colony

grows vertically. To see the elevation of the colonies, it may be helpful to look through the side of the petri dish. The descriptors here are flat, raised, convex (sloping up from the edges), pulvinate (sloping steeply from the edges and very high in the center), and umbonate (has a raised center)

Colony Morphology

• Edge, or margin, describes the borders of the colony. The edge can be entire (smooth, with no projections), undulate (wavy), lobate (lobed), filamentous, or rhizoid.

Colony Morphology

• Color/Pigment– Some bacteria produce pigments, giving the colony a

distinct color. Pigments can span the entire color spectrum. Recording the color is the first step. In addition to describing the color, this is also the time to identify if the colony is opaque (you can't see through it), translucent (you can see through it), dull, or shiny.

• Texture– Texture refers to the characteristics of the colony

surface. Colonies can be dry, mucoid (thick, stringy, and wet), moist, smooth, rough, rugose (wrinkled), or contain concentric rings.

Useful Terminology

• Normal Flora: microorganisms that are typically present in a particular environment– Ex: Staphylococcus epidermidis is found on

essentially every surface of the human body

• Contaminants: transients organisms that are often invaders in a particular environment