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Which phase represents exponential growth?
Which method of determining growth rate is an indirect method?
What indicates the original milk sample contained if one milliliter of the third dilution tube plated has 54 colonies?
5400 cells per milliliter
Saccharomyces cerevisiae grows best at which pH range?
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Which of the following growth requirements allows microorganisms to survive in oxygen but they cannot grow?
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Which of the following terms refers to culture medium that exhibits no living microbes?
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Most pathogenic bacteria are thermophiles.
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Which of the following temperature classifications of microorganisms contains human pathogens?
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Which of the following is NOT a trace element?
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Which type of media suppresses unwanted microbes and encourages desired microbes?
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Which of the following is needed for synthesis of cell membranes and nucleic acids?
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Which method of determining growth rate requires the presence of colony-forming units after a series of culture dilutions?
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An obligate halophile requires which of the following growth conditions?
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Which pH range is good for Escherichia coli?
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Agar is used as a solidifying agent in microbiological media since few bacteria can degrade it.
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If cells are grown in media containing amino acids labeled with radioactive nitrogen (15N), most of the radioactivity will be found in the cells'
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Which of the following pairs is mismatched?
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Which of the following terms means to inhibit microbes without necessarily killing them?
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All of the following are methods of food preservation EXCEPT?
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Which of the following microbial structures is only found in mycobacteria?
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Ethylene oxide is:
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Which of the following terms means destroying harmful microorganisms usually from surfaces?
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Which of the following terms means the mechanical removal of microbes from a limited area?
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Which of the following physical microbial control methods does not involve heat?
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Which of the following has no bearing on the effectiveness of treatment to remove or reduce microbes?
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Which of the following is NOT an action of microbial control agents?
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Which of the following methods is used to determine the efficacy of chemical agents?
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Which of the following terms means the removal and destruction of all microbial life?
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Which of the following structures is resistant to autoclaving?
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Binary fission is used in which of the following DNA transfers?
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Study Notes
Bacterial Growth Phases
- Log Phase represents exponential growth.
- Lag Phase is a period of adaptation, not exponential growth.
- Death Phase represents a decline in population due to a lack of resources or unfavorable conditions.
Determining Bacterial Growth Rates
- Direct microscopic count is a method that directly counts cells using a microscope.
- Plate count is a method that determines the number of viable bacteria by counting colonies on a plate.
- Most Probable Number (MPN) is an indirect method that estimates the number of viable bacteria in a sample.
- Turbidity measures the cloudiness of a bacterial culture, which correlates to cell density.
- Filtration is a method used to concentrate bacteria from a liquid sample onto a filter, which is then counted.
Plate Count Example
- A 1:10 dilution series means that each subsequent dilution tube has 1 part of the previous tube and 9 parts of fresh medium.
- If 54 colonies grew on the plate from the 3rd dilution, the original milk sample contained 54,000 cells per milliliter (54 x 10 x 10 x 10).
Growth Requirements
- Saccharomyces cerevisiae (yeast) grows best in a pH range of 6.5-7.5.
- Obligate anaerobes cannot survive in the presence of oxygen.
- Obligate aerobes require oxygen for growth.
- Facultative anaerobes can grow with or without oxygen, but prefer oxygen.
- Microaerophiles require low oxygen levels.
- Aerotolerant anaerobes tolerate oxygen but do not use it for growth.
Culture Media
- Sterile media refers to a medium that is free from any living microbes.
- Agar is a solidifying agent often used in culture media.
- Inoculum refers to a small amount of microbes introduced into a culture medium.
Temperature Classification of Microorganisms
- Mesophiles are microorganisms that grow best at moderate temperatures (20-45°C) and include many human pathogens.
- Psychrophiles prefer cold temperatures.
- Psychrotrophs can tolerate cold temperatures but grow best at moderate temperatures.
- Thermophiles prefer hot temperatures.
Trace Elements and Growth Requirements
- Trace elements are needed in small amounts for microbial growth.
- Examples of trace elements include zinc, molybdenum, and enzyme cofactors.
- Sulfur is required for the synthesis of amino acids and proteins.
- Carbon is the backbone of all organic molecules.
- Nitrogen is needed for the synthesis of amino acids and nucleic acids.
- Phosphorus is essential for the synthesis of nucleic acids and cell membranes.
Selective Media
- Selective media inhibits the growth of unwanted microbes and encourages desired microbes.
- Differential media allows for the differentiation of different bacteria based on their growth characteristics.
Growth Conditions
- Obligate halophiles require a hypertonic environment with a high salt concentration for growth.
Escherichia coli pH Range
- Escherichia coli grows well in a pH range of 6.5-7.5.
Agar as a Solidifying Agent
- Agar is an effective solidifying agent for microbiological media because most bacteria cannot degrade it.
Radioactive Nitrogen (15N)
- When cells are grown in the presence of radioactive nitrogen, most of the radioactivity will be found in the cells' DNA and proteins.
Antimicrobial Agents
- Ag (silver) is used in wound dressings for its antimicrobial properties.
- CuSO4 (copper sulfate) is an algicide used to kill algae.
- H202 (hydrogen peroxide) is used for its antimicrobial properties on open wounds.
- Alcohols are commonly used as antiseptics for open wounds.
Microbial Control Terms
- Bacteriostasis means to inhibit the growth of microbes without necessarily killing them.
- Antisepsis is the destruction of harmful microorganisms typically from living tissue.
- Sanitization refers to the reduction of microbial numbers to a safe level on inanimate objects.
- Degerming is the mechanical removal of microbes from a limited area.
Food Preservation
- High pressure, desiccation (drying), osmotic pressure, and ionizing radiation are all methods of food preservation.
- Microwaves are not a reliable method of food preservation, as they do not kill all microbes.
Microbial Structures
- Waxy cell walls characteristic of Mycobacteria, give them resistance to antimicrobial agents.
- LPS (lipopolysaccharide) is a component of the outer membrane of Gram-negative bacteria.
- Prions are infectious proteins that can cause disease.
- Endospores are dormant, resistant structures produced by some bacteria.
Ethylene Oxide
- Ethylene oxide is a sterilizing agent that can kill spores.
- Ethylene oxide does not require high heat and is effective against a wide range of microbes.
Microbial Control Methods
- Biocide (Germicide) refers to the destruction of harmful microorganisms.
- Sterilization is the removal and destruction of all microbial life.
- Disinfection is the destruction of harmful microorganisms from surfaces.
- Antisepsis is the destruction of harmful microorganisms typically from living tissue.
Physical Microbial Control Methods
- Incineration involves burning to destroy microbes.
- Pasteurization uses moderate heat to destroy harmful microbes in liquids.
- Autoclaving uses pressurized steam to sterilize materials.
- Membrane filtration physically removes microbes from liquids or gases by passing them through a filter.
- Membrane filtration does not involve heat.
Factors Affecting Microbial Control
- The environment, the number of microbes, and the time of exposure all influence the effectiveness of microbial control measures.
- The cost of a microbial control method is not a factor in its effectiveness.
Actions of Microbial Control Agents
- Microbial control agents can alter microbial reproduction, damage proteins, alter membrane permeability, or damage nucleic acids.
Determining Efficacy of Chemical Agents
- Disk-diffusion method is one way to determine the effectiveness of chemical agents.
- The method involves placing antibiotic discs on a bacterial plate and observing the zones of inhibition around the discs.
Sterilization
- Sterilization is the complete elimination of all living organisms, including spores.
- Endospores are highly resistant to heat and chemicals.
- Autoclaving is a reliable method of sterilization.
Binary Fission
- Binary fission is the process by which bacteria divide into two identical daughter cells.
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Description
Explore the different phases of bacterial growth, including log, lag, and death phases. Learn about various techniques used to determine bacterial growth rates, including direct microscopic count and plate count methods. This quiz will test your understanding of these fundamental concepts in microbiology.
