Lab 1 – Part 1: Media Types and Uses

What is media and why do we need it in lab? Microorganisms need nutrients, a source of energy and certain environmental conditions in order to grow and reproduce. Growth Medium – a liquid or gel designed to support the growth of microorganisms. Growth medium is required in order to culture and observe microorganisms in the laboratory. Bacterial growth on agar plate Growth medium (nutrient agar plate)

Media in a Tube Broth: a liquid medium Slant: tube of solid medium at an angle Agar deep: tube of solid or semi-solid medium Broth Slant Deep

Media on a Plate Nutrient agar plate: solid medium on flat surface. This is the best method to observe colony morphology (shape) and to work with individual colonies. Best for diagnostic methods. Nutrient Agar Plate Bacterial colony

Types of Media Enriched – selects for certain microorganisms by including a nutrient that the desired microorganism or group can use and its competitors can not. Selective – selects for growth of certain microorganisms in a mixed population by using an ingredient that inhibits the growth of other microorganisms, but not the desired species or group. Differential – does not select for any particular group by inhibiting or enhancing their growth over competitors, but it does show a visible difference (for example color) between or among groups of microorganisms. **Some media can be 1, 2, or all of the above.

Selective Differential

Specific Types of Media used in Microbiology For a list of specific types of media used in Microbiology see your handout. We will be using many of these throughout the semester so please refer back to this page when necessary. Blood Agar Chocolate Agar

Lab 1 – Part 2: Use and Care of the Microscope

The Microscope Simple Microscope – one lens (like a magnifying glass) A device used to magnify objects that are too small to be seen with the naked eye Simple Microscope – one lens (like a magnifying glass) Compound Microscope – two or more sets of lenses Simple Compound

Parts of a Compound Microscope

Important Terms for the Microscope Specimen: the object that is being looked at Ocular lens: eyepiece Objective lens: lens closest to the specimen Condenser: lens that concentrates the light for better resolution of the specimen Iris diaphragm: controls the amount of light Rheostat: controls intensity of light Course adjustment: used for focusing with low power objective lens Fine adjustment: used for focusing with high power and oil immersion lens Parfocal – specimen will remain in focus as you change the objective lenses Resolution – the ability of the lenses to reveal fine detail

Magnification on a Compound Microscope Compound microscopes have 3-4 objective lenses: Scanning (4x), low power (10x), high power dry (40x), and oil immersion (100x) The ocular lens (eyepiece) has a magnification of 10x. To determine the total magnification you multiply the ocular lens magnification (10x) times the objective lens (4x) to get a total of 40x magnification.

Determining Total Magnification

Magnification on a Compound Microscope Oil Immersion: To use a 100X objective lens, a drop of oil is placed between the specimen and the scope in order to decrease bending of the light rays (refraction).

How does a microscope work?

Basic Bacteria Morphologies

Basic Bacterial Arrangements

Lab Procedure: Viewing Prepared Slides Pages 8-9 (refer to page numbers at the top) Follow the procedure to observe microorganisms on prepared microscope slides Prepared microscope slide

Assignments Lab Report – Use of the Microscope Record your observations in the circles provided Answer question #1

Lab 1 - Part 2

Lab Procedure: Preparing and Viewing a Wet Mount of Yeast and Bacteria (to be done in lab session #2) Follow the procedure in your lab manual on page 9, substitute the pond water for a test tube mixture of yeast and bacteria. Place a small drop of the yeast and bacteria mixture on a glass slide and add a coverslip over the drop. Place the slide on the microscope stage and rotate the 10X objective over the coverslip. Adjust the rheostat and iris diaphragm to reduce the light intensity as less light is needed at this magnification. Focus on the edge of the coverslip at first then move to the interior; this will help to bring the cells into view. Continue adjusting the light. When you have the specimen in focus, confirm the cell types under the 40X objective. Adjust the light intensity again. Adjust the fine focus knobs to bring the cells into view. Yeast cells appear as small bubbles that are oval, round, or elongated. They will vary in size and may be individual cells, or grouped in pairs, chains or clusters. Yeast are at least 3-4 times larger than bacteria; bacteria will appear as small grainy cocci or rods in the background.

Yeast Yeast Bacteria