Microbiology: Bacterial Colonies and Growth

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Aseptic Technique

• Good aseptic technique includes sterilizing the inoculating loop before and after use.
• Decontaminating the lab bench before and after use is important.
• Flaming the inoculating loop for at least 10 seconds before a bacterial transfer is crucial.
• Flaming the top of a tube before and after inoculating a culture creates upward air currents.

Scientists Inoculate Various Types of Media to Grow Microorganisms

• Different types of media are used to grow microorganisms (liquid, semisolid, solid/reversible to liquid).

After Incubation, Bacteria Grow in Colonies on Solid Surfaces

• Bacteria grow in colonies visible to the naked eye after incubation.
• A single bacterial cell gives rise to a colony with millions of cells.
• Colonies are visible as isolated units of millions of cells on solid surfaces.

A Bacterial Colony

• A bacterial colony is macroscopic and visible to the naked eye.
• A bacterial colony generally is composed of many cells.
• A bacterial colony typically originates from a single bacterial cell.

Cell Shape (Microscopic) and Colony Shape (Macroscopic) Are Not the Same

• The microscopic shape of cells.
• The macroscopic shape of bacterial colonies.

The Streak Plate Method is Commonly Used to Obtain Isolated Colonies

• The streak plate method is used to isolate colonies of bacteria.
• Sterilizing the spreading tool after each step is essential for this method (an inoculating loop).

Microbes Must Have All of Their Required Nutrients In Order to Grow

• General-purpose media: Grow various microbes with complex ingredients supporting different types of microbial life.
• Limiting Resources: Essential elements, water, food, and oxygen. A resource can limit growth.

Microbes Must Have All of Their Required Nutrients In Order to Grow-Enriched Media

• Enriched media typically contain complex organic substances (like blood, serum, or hemoglobin) that help fastidious bacteria grow or special growth factors.
• Blood agar is an enriched media that has different types of hemolysis: alpha (partial lysis), beta (complete lysis), and gamma (no lysis).

Some Media Are Used to Grow Specific Types of Microorganisms

• General-purpose nonselective media support diverse microbial growth.
• Selective media promote growth while inhibiting others.

Some Media Are Used to Differentiate Different Types of Microorganisms

• Nondifferential media display similar appearance from different microbial species.
• Differential media enable species distinctions based on differing reactions.

Some Media, like MacConkey Agar, are Both Selective and Differential

• MacConkey Agar is selective for gram-negative bacteria and differential based on lactose fermentation.
• Lactose fermenters appear pink.
• Non-lactose fermenters appear off-white.

Staining is Used to Help Visualize Cells

• Simple stains reveal cell size, shape, and arrangement.
• Differential stains reveal differences between different bacterial types (e.g., gram-positive vs. gram-negative). Acid-fast or endospore stains can also be used for these distinctions.

Gram-Positive Cells Stain Purple While Gram-Negative Cells Stain Pink

• Cell walls differ in structure between gram-positive and gram-negative bacteria.

The Gram Stain Is a Differential Stain That Can Distinguish Gram-Positive and Gram-Negative Cell Wall Structures

• The Gram stain procedure uses reagents and multiple steps to distinguish between gram-positive and gram-negative bacteria.

In a Controlled Setting, Bacteria Grow in a Predictable Pattern Known as a Growth Curve

• The growth curve exhibits distinct phases including lag, exponential, stationary, and death.

The Lag Phase of the Growth Curve is a Period of Adjustment and Synthesis. Cells are Not Multiplying at Their Maximum Rate

• Cells adjust before exponential growth begins.

The Log or Exponential Phase of the Growth Curve Will Continue as Long as Environmental Conditions and Nutrition are Favorable

• Sufficient favorable conditions allow bacteria to reproduce exponentially.

During the Stationary Phase of the Growth Curve, Cells Enter Survival Mode and Grow Slowly

• In this phase, growth slows, and cell reproduction rates equal death rates.

During the Death Phase of the Growth Curve, Cells Die at an Exponential Rate

• During the death phase, the death rate for cells increases exponentially.

Biosafety Levels are a System of Categories Adopted by the CDC Based on the Relative Danger of the Pathogen

• Biosafety levels categorize pathogens based on their risk.
• BSL-1 agents and microorganisms pose little risk. BSL-4 agents pose significant risk, requiring elaborate precautions.

Phagocytic Cells Clear Debris and Engulf Pathogens

• Monocytes circulate and turn to macrophages or dendritic cells.
• Macrophages have high capacity for killing microbes.
• Dendritic cells reside in tissues to process foreign material and present antigens.
• Neutrophils are the first responders to bacterial infections.
• Eosinophils are phagocytes but do so inefficiently.

Antibody Molecules BIND (They Do Not Kill)

• Antibodies bind to antigens.
• Opsonization helps phagocytes recognize microbes.
• Neutralization prevents microbes from attaching.
• Agglutination renders microbes immobile.
• Antitoxins neutralize bacterial exotoxins.

When Activated, Cytotoxic T Cells Kill Infected Self-Cells

• Cytotoxic T cells kill infected cells.
• Perforins create holes in cell membranes.
• Granzymes enter cells and trigger apoptosis.

Sterilization Kills All Organisms. Pasteurization Reduces Spoilage Organisms. Food Spoils Due to Acid Production by Spoilage Organisms.

• Specific heat and time parameters for different sterilization and pasteurization processes are mentioned but not presented in summary.

Biochemical Tests Help Identify Microbes

• Biochemical tests help identify microbes by determining their function.
• Some tests include motility, oxidase, fluid thioglycollate, urea, and tryptophan tests. A catalase test will produce bubbles if the enzyme catalase is produced.

Describe This Organism

• Gram-negative rods: Gram stain, motility, catalase, indole tests. Other tests are identified based on the description of the given organism for a species identification.

Test your knowledge on bacterial colonies and their characteristics in microbiology. This quiz covers various aspects such as the origin of isolated colonies, staining techniques, and growth phases. Perfect for students and professionals looking to reinforce their understanding of bacterial growth and classification.