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Microbiology an Introduction

  • Title: Microbiology an Introduction

  • Edition: Thirteenth Edition

  • Authors: Tortora, Funke, Case

Chapter 6: Microbial Growth

  • Focus: Requirements for microbial growth and related concepts

Serratia Marcescens Bacteria

  • Category: Bacterial species discussed in relation to growth cycles

Requirements for Growth (Learning Objectives)

Learning Objectives

  • 6-1: Classify microbes into five preferred temperature ranges.

  • 6-2: Identify the control of pH in culture media and its significance.

  • 6-3: Explain osmotic pressure's role in microbial growth.

Physical Requirements

  • Temperature

  • pH

  • Osmotic pressure

Chemical Requirements

  • Carbon

  • Nitrogen, sulfur, and phosphorus

  • Trace elements

  • Oxygen

  • Organic growth factors

Physical Requirements of Microbial Growth

Temperature (1 of 2)

  • Minimum growth temperature

  • Optimum growth temperature

  • Maximum growth temperature

Temperature (2 of 2)

  • Psychrophiles: Cold-loving microbes

  • Mesophiles: Moderate-temperature-loving microbes

  • Thermophiles: Heat-loving microbes

Typical Growth Rates of Microorganisms by Temperature

  • Data indicating how different organisms respond to varying temperatures

Psychrotrophs

  • Temperature range: 0°C to 20-30°C

  • Commonly associated with food spoilage

Temperature Preservation Levels

  • Destruction of most microbes at specific temperatures.

  • Danger zone: Temperature at which bacteria thrive.

Thermophiles and Hyperthermophiles

  • Thermophiles: Optimum growth at 50°C-60°C found in hot springs.

  • Hyperthermophiles: Optimum growth at temperatures exceeding 80°C.

pH and Microbial Growth

  • Most bacteria: Optimal at pH 6.5-7.5.

  • Molds and yeasts: Optimal at pH 5-6.

  • Acidophiles: Microbes thriving in acidic conditions.

Osmotic Pressure

  • Hypertonic environments: Can cause plasmolysis, harming microbial cells.

  • Extreme or obligate halophiles: Require high salt concentrations.

  • Facultative halophiles: Can thrive in high osmotic pressures.

Plasmolysis Illustration

  • Visual representation of plasmolysis in hypertonic solutions impacting cell growth.

Check Your Understanding-1

Questions

  1. Why are hyperthermophiles limited to oceanic depths?

  2. Advantages of phosphate salts as buffers?

  3. Use of osmotic pressure in primitive food preservation?

Chemical Requirements for Growth (Learning Objectives)

Learning Objectives

  • 6-4: Identify uses of carbon, nitrogen, sulfur, and phosphorus in microbial growth.

  • 6-5: Classify microbes based on their oxygen requirements.

  • 6-6: Explain how aerobes mitigate damage from toxic oxygen forms.

Chemical Requirements (1 of 3)

  • Carbon: Structural backbone of organic molecules

  • Chemoheterotrophs: Utilize organic molecules for energy

  • Autotrophs: Use CO2 for carbon source

Chemical Requirements (2 of 3)

  • Nitrogen: Essential for proteins, DNA, ATP. Sources include protein decomposition and nitrogen fixation.

Chemical Requirements (3 of 3)

  • Sulfur: Necessary for amino acids and vitamins.

  • Phosphorus: Vital for DNA, RNA, ATP, and membranes.

Trace Elements

  • Definition: Inorganic elements required in small quantities.

  • Functions: Often act as enzyme cofactors (e.g., iron, copper).

Oxygen Requirements

Oxygen (1 of 2)

  • Obligate aerobes: Require oxygen for growth.

  • Facultative anaerobes: Ferment or anaerobically respire in absence of oxygen.

  • Anaerobes: Harmed by oxygen.

  • Aerotolerant anaerobes: Tolerate oxygen but do not utilize it.

  • Microaerophiles: Require lower oxygen concentration than ambient air.

Oxygen (2 of 2)

  • Reactive oxygen species: Various toxic forms (singlet oxygen, superoxide radicals)

Organic Growth Factors

  • Compounds obtained from the environment, including vitamins and amino acids necessary for growth.

Check Your Understanding-2

Questions

  1. Where would radioactive sulfur be found in bacterial cells?

  2. How to determine if a microbe is a strict anaerobe?

  3. Methods for microbes to avoid oxygen damage?

Biofilms (Learning Objective 6-7)

Understanding Biofilms

  • Definition: Microbial communities forming slime or hydrogels on surfaces.

  • Bacteria communicate via quorum sensing and share nutrients.

  • Provide shelter from harmful environmental conditions.

Characteristics of Biofilms

  • Found in sewage systems and digestive systems; can cause clogging.

  • Exhibit high resistance to microbial control methods (1000x more resistant).

  • Contribute to 70% of infections (e.g., catheter-associated, dental caries).

Check Your Understanding-3

Questions

  • Identify advantages of biofilm formation for pathogens.

Culture Media (Learning Objectives)

Learning Objectives

  • 6-8: Distinguish between chemically defined and complex media.

  • 6-9: Justify various anaerobic and selective methods in culture.

  • 6-10: Differentiate biosafety levels.

Culture Medium Overview

  • Components and characteristics of culture media for microbial growth.

  • Sterile: No living microbes present.

  • Inoculum: Introduction of microbes into culture media.

  • Culture: Microbes growing in/on a medium.

Role of Agar

  • Agar serves as a solidifying agent, not metabolized by microbes.

Types of Media

  • Chemically defined media: Exact chemical composition is known.

  • Complex media: Varies chemically due to organic extracts.

Check Your Understanding-4

Questions

  1. Could humans survive on chemically defined media?

  2. Feasibility of growing rabies in cell cultures historically?

  3. What is the biosafety level of your laboratory?

Obtaining Pure Cultures (Learning Objectives)

Learning Objectives

  • 6-11: Define colony and describe methods to isolate pure cultures.

Definition and Methods

  • Pure culture: Contains only one type of organism.

  • Colony: Population of cells from a single cell or spore.

  • Streak Plate Method: Used for isolating pure cultures.

Preserving Bacterial Cultures (Learning Objectives)

Learning Objectives

  • 6-13: Explain preservation methods like deep-freezing and lyophilization.

Preservation Methods

  • Deep-freezing: Between -50°C to -95°C.

  • Lyophilization: Freeze-dried under vacuum conditions.

Bacterial Growth Phases (Learning Objectives)

Learning Objectives

  • 6-14: Define bacterial growth and binary fission.

  • 6-15: Compare phases of microbial growth.

Bacterial Division Overview

  • Methods of division include binary fission, budding, and fragmentation.

Generation Time

  • Time taken for a bacterial cell to divide, can range from 20 minutes to 24 hours.

Phases of Growth

  • Lag Phase: Preparation for growth.

  • Log Phase: Exponential growth.

  • Stationary Phase: New cells balance deaths.

  • Death Phase: Decline in numbers.

Check Your Understanding-7

Questions

  • Can complex organisms divide by binary fission?

Direct Measurement of Microbial Growth

Techniques

  • Plate count: Counts colonies on plates; ideal range is 30-300 colonies.

  • Filtration: Captures bacteria from liquids.

  • MPN Method: Multiple tube test for statistical estimates.

  • Direct microscopic counts: Volume of bacterial suspension counted.

Check Your Understanding-9

Questions

  • Challenges of measuring filamentous molds by plate count.

Estimating Bacterial Numbers by Indirect Methods

Techniques

  • Turbidity measurement: Estimation using a spectrophotometer.

  • Metabolic activity: Measurement based on metabolic products.

  • Dry weight: Used for filamentous organisms.

Check Your Understanding-10

Questions

  • Issues with using direct methods for food analysis.

  • Feasibility of determining vitamin content in products.