Lab 10 & 11: Selective Media and Serial Dilutions

Nutritive Media

Supports growth of a wide range of microorganisms.

Enriched Media

Contains additives to enhance growth of specific organisms.

Selective Medium

Supports one group while inhibiting another.

Differential Media

Shows different characteristics for distinguishing organisms.

EMB Agar

Selective for Gram-; differentiates lactose fermenters.

Mannitol Salt Agar

Selective for Staphylococcus; differential for mannitol fermentation.

MacConkey Agar

Selective for Gram-; differentiates lactose fermenters.

Phenylethyl Alcohol Agar

Selective for Gram+; inhibits most Gram- organisms.

Lactose Fermenter

Produces acid; colonies appear dark or colored.

Non-Lactose Fermenter

Increases pH; colonies appear colorless or light.

Bile Salt

Inhibits growth of most Gram+ bacteria.

Crystal Violet Dye

Inhibits Gram+ bacteria in MacConkey Agar.

Neutral Red Dye

pH indicator; turns pink with lactic acid.

Mannitol Fermenter

Produces acid; changes phenol red to yellow.

Staphylococcus aureus

Pathogenic species that ferments mannitol.

Gram- Bacteria

Bacteria that do not retain crystal violet stain.

Gram+ Bacteria

Bacteria that retain crystal violet stain.

Eosin Methylene Blue

Contains eosin and methylene blue dyes.

Growth Factors

Nutrients that enhance microbial growth.

Blood Agar

Enriched media used for growing fastidious organisms.

Physical Characteristics

Visible traits used to differentiate bacterial species.

Phenylethyl Alcohol

Disrupts lipid membranes in Gram-negative bacteria.

Selective-Differential Media

Media that selects for specific organisms and differentiates them.

EMB Agar

Eosin Methylene Blue agar for Gram-negative bacteria.

MacConkey Agar

Selective for Gram-negative, differentiates lactose fermenters.

Mannitol Salt Agar

Selective for Staphylococci; differentiates mannitol fermenters.

PEA Agar

Phenylethyl Alcohol agar inhibits Gram-negative growth.

Aseptic Technique

Method to prevent contamination during inoculation.

Inoculation

Introducing microorganisms into a culture medium.

Incubation

Maintaining cultures at specific temperatures for growth.

Blood Agar

Nutritive medium with differential hemolysis properties.

Hemolysis

Destruction of red blood cells by bacteria.

Alpha Hemolysis

Partial lysis; greenish discoloration in agar.

Beta Hemolysis

Complete lysis; transparent area around colonies.

Gamma Hemolysis

No lysis; no change in agar appearance.

Candle Jar

Creates hypoxic environment for capnophilic bacteria.

Capnophilic Bacteria

Require elevated carbon dioxide levels for growth.

Staphylococcus epidermidis

Coagulase-negative staphylococcus, skin commensal.

Escherichia coli

Common Gram-negative bacterium, lactose fermenter.

Proteus vulgaris

Gram-negative bacterium, known for swarming motility.

Staphylococcus aureus

Pathogenic coagulase-positive staphylococcus.

Streptococcus pyogenes

Beta-hemolytic streptococcus, causes strep throat.

Streptococcus pneumoniae

Alpha-hemolytic, causes pneumonia and meningitis.

Unknown Organism

One of the specified organisms, to be identified.

Fecal Coliform Bacteria

Bacteria from warm-blooded animals' intestines.

Colony Forming Units (CFU)

Units measuring viable bacteria per 100 mL.

Water Quality Standards

Regulations for maximum fecal coliform levels.

Serial Dilution

Sequential dilutions to reduce bacterial concentration.

Agar Plate

Medium for growing bacterial colonies.

Viable Cells

Living bacteria capable of growth.

Statistical Significance

Range of 30-300 colonies for counting.

Dilution Factor

Amount by which a sample is diluted.

Incubation

Process of allowing bacteria to grow.

Transfer Pipette

Tool for transferring liquid samples accurately.

Vortex Mixer

Device for mixing solutions thoroughly.

Lake Water Sample

Source of bacteria for testing.

Counting Colonies

Determining number of visible bacterial growths.

1:10 Dilution

Dilution reducing concentration by a factor of 10.

1:100 Dilution

Dilution reducing concentration by a factor of 100.

1:10000 Dilution

Dilution reducing concentration by a factor of 10,000.

Bacterial Concentration

Amount of bacteria in a given volume.

Spreading Rods

Tools for evenly distributing samples on agar.

Water Blanks

Sterile water used for dilutions.

Visible Isolated Colonies

Distinct bacterial growths on agar plates.

Maximum Levels

Regulatory limits for bacteria in water.

Disease-Producing Organisms

Pathogens potentially present with fecal contamination.

Serial Dilution

Process of reducing concentration stepwise.

Dilution Factor (DF)

Ratio of sample volume to final volume.

Vi

Original volume of the sample added.

Vf

Final volume after dilution.

1:1 Dilution

Equal parts of sample and diluent.

1:10 Dilution

One part sample to nine parts diluent.

1:100 Dilution

One part sample to ninety-nine parts diluent.

1:1000 Dilution

One part sample to nine hundred ninety-nine parts diluent.

1:10,000 Dilution

One part sample to nine thousand nine hundred ninety-nine parts diluent.

Agar Plate

Solid medium for growing microorganisms.

Colony

Visible mass from rapid cell division.

CFU/ml

Colony Forming Units per milliliter.

Calculation of CFU/ml

Formula to determine viable cells concentration.

Volume Plated

Amount of sample spread on agar plate.

Incubation

Process of maintaining conditions for growth.

Spreading Rod

Tool for evenly distributing liquid on plates.

Visible Mass

Group of cells forming a colony.

Count Colonies

Determine number of bacteria in diluted solution.

Original Sample

Initial concentration before dilution.

Viable Cells

Living cells capable of division.

Successive Dilutions

Repeated dilution using previous dilution.

Calculation Example

Illustrates CFU/ml using specific data.

Dilution Calculation

Method to find dilution factor mathematically.