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Boundless Microbiology
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Microbiology

Chapter 6

Culturing Microorganisms

Book Version 6
By Boundless
Boundless Microbiology
Microbiology
by Boundless
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Section 1
Microbial Nutrition
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Chemical Analysis of Microbial Cytoplasm

Microbial cytoplasm is contained within the cytoplasmic membrane and includes the cytosol, macromolecules, and inclusions.

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Sources of Essential Nutrients

The sources of common essential nutrients are carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur.

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Limitation of Microbial Growth by Nutrient Supply

Nutrients are necessary for microbial growth and play a vital role in culturing microorganisms outside of their natural environment.

Section 2
Cell Differentiation and Starvation
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Activation of Starvation by Survival Genes

Stringent response is a stress response that occurs in bacteria and plant chloroplasts in reaction to stress conditions.

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Oligotrophs

Oligotrophs are characterized by slow growth, low rates of metabolism, and generally low population density.

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Starvation-Induced Fruiting Bodies

Starvation-induced fruiting bodies can aggregate up to 500 micrometres long and contain approximately 100,000 bacterial cells.

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Bacterial Differentiation

Several bacteria alter their morphology in response to the types and concentrations of external compounds.

Section 3
Culturing Bacteria
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Culture Media

Culture media is the food used to grow and control microbes.

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Complex and Synthetic Media

In defined media all the chemical compounds are known, while undefined media has partially unknown chemical constituents.

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Selective and Differential Media

Selective media allows for the growth of specific organisms, while differential media is used to distinguish one organism from another.

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Aseptic Technique, Dilution, Streaking, and Spread Plates

Microbiologists rely on aseptic technique, dilution, colony streaking and spread plates for day-to-day experiments.

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Special Culture Techniques

Many microbes have special growth conditions or require precautions to grow in a laboratory setting, leading to special culture techniques.

Section 4
Microbial Culture Methods
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Enrichment and Isolation

Understanding the nutritional requirements of bacteria can aid their enrichment and isolation.

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Pure Culture

A pure culture is a population of cells or multicellular organisms growing in the absence of other species or types.

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Preserving Bacterial Cultures

Bacteria can be stored for months or years if they are stored at -80C and in a high percentage of glycerol.

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The FISH Technique

FISH is a hybridization technology which allows the labeling of target RNAs with a fluorescent probe.

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Coupling Specific Genes to Specific Organisms Using PCR

PCR allows for the amplification and mutation of DNA and allowing researchers to study very small samples.

Section 5
Bacterial Identification
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Chemical Assays, Radioisotopic Methods, and Microelectrodes

There are numerous tests and assays available that are utilized to aid in bacterial identification in a variety of settings.

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Stable Isotopes

Stable isotopes are atoms that are not radioactive, in other words, they are not going to lose neutrons and decay spontaneously.

Section 6
Microbial Growth
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Binary Fission

Binary fission is the method by which prokaryotes produce new individuals that are genetically identical to the parent organism.

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Fts Proteins and Cell Division

FtsZ is a protein encoded by the ftsZ gene that assembles into a ring at the future site of the septum of bacterial cell division.

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MreB and Determinants of Cell Morphology

MreB is a protein found in bacteria homologous to actin.

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Peptidoglycan Synthesis and Cell Division

Peptidoglycan, also known as murein, is a polymer and consists of sugars and amino acids which form the cell walls of bacteria.

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Generation Time

Bacterial growth occurs by the division of one bacterium into two daughter cells in a process called binary fission.

Section 7
Bacterial Population Growth
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Microbial Growth Cycle

Increases in cell size are tightly linked in unicellular organisms and under optimal conditions bacteria can grow and divide rapidly.

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Growth Terminology

The two ways that microbial organisms can be classified are as autotrophs (supply their own energy) or as heterotrophs (use the products of others).

Section 8
Counting Bacteria
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Direct Counting

Direct counting methods are used to determine bacterial concentration without the need for advanced equipment.

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Viable Cell Counting

Plate counting is used to estimate the number of viable cells that are present in a sample.

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Measurements of Microbial Mass

Changes in the number of bacteria can be calculated by a variety of methods that focus on microbial mass.

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Detecting Acid and Gas Production

Culture media can be used to differentiate between different kinds of bacteria by detecting acid or gas production.

Section 9
Temperature and Microbial Growth
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Growth Rate and Temperature

Bacteria may grow across a wide range of temperatures, from very cold to very hot.

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Classification of Microorganisms by Growth Temperature

Bacteria can be classified on the basis of cell structure, metabolism or on differences in cell components.

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The Heat-Shock Response

Heat shock response is a cell's response to intense heat, including up-regulation of heat shock proteins.

Section 10
Other Environmental Growth Factors
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Gas Requirements

Cells are grown and maintained at an appropriate temperature and gas mixture of oxygen, carbon dioxide, and nitrogen in a cell incubator.

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Osmotic Pressure

The correct osmotic pressure in the culture medium is essential for the survival of the cells.

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Microbial Growth at Low or High pH

Microorganisms live and thrive within specific pH levels.

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Oxygen

Oxygen requirements vary among microorganisms.

Section 11
Microbial Growth in Communities
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Ecological Associations Among Microorganisms

Despite an apparent simplicity, bacteria can form complex associations with other organisms.

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Biofilms

A biofilm is an aggregate of microorganisms in which cells adhere to each other on a surface.

Section 12
Control of Microbial Growth
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Considerations in Microbial Control

Controlling microbial growth is important in many fields but the degree of acceptable microbial levels can be quite different.

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Rate of Microbial Death

The rate of microbial death is used to develop standard protocols for sterilization in many industries.

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Relative Resistance of Microbes

Different microbial structures and types of microbial cells have different level of resistance to antimicrobial agents.

Section 13
Mechanisms of Microbial Control
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Alteration of Membrane Permeability

The lipid portion of the outer membrane is impermeable to charged molecules.

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Damage to Proteins and Nucleic Acids

A bacteriostatic agent is a biological or chemical agent that stops bacteria from reproducing by targeting DNA replication and proteins.

Section 14
Physical Antimicrobial Control
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Heat

Heat is one of the most common and easily available methods for controlling bacterial growth.

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Radiation

Both non-ionizing and ionizing radiation methods are applied for sterilization.

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Low Temperatures

Low temperatures usually inhibit or stop microbial growth and proliferation but often do not kill bacteria.

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High Pressure

Under very high hydrostatic pressure(HHP) of up to 700 MPa, water inactivates pathogens such as E. coli and Salmonella.

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Desiccation

Desiccation is the state of extreme dryness, or the process of extreme drying and can be used to control microbial growth.

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Osmotic Pressure

Osmotic pressure is the pressure which must be applied to a solution to prevent the inward flow of water across a semipermeable membrane.

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Filtration

Fluids that would be damaged by heat, irradiation, or chemical sterilization can be sterilized by microfiltration using membrane filters.

Section 15
Chemical Antimicrobial Control
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Effective Disinfection

A perfect disinfectant would offer full microbiological sterilisation, without harming humans and would also be non-corrosive.

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Factors that Affect Germicidal Activity of Chemicals

Some antiseptics are germicides, capable of destroying microbes (bacteriocidal), while others are bacteriostatic and prevent their growth.

Types of Disinfectants

There are multiple types of disinfectants, including but not limited to air disinfectants, alcohols, and oxidizing agents.

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Biological Control of Microbes

Prior to the advent of antibiotics, live organisms were used directly in attempts to control microbial infections.

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Microbial Metabolism
  • Types of Metabolism
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Chapter 6
Culturing Microorganisms
  • Microbial Nutrition
  • Cell Differentiation and Starvation
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  • Microbial Culture Methods
  • Bacterial Identification
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Microbial Genetics
  • Genes
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