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Questions and Answers
What occurs in the process of microbial growth?
Which factor significantly influences bacterial life and metabolism?
Which medical devices are known to potentially harbor biofilms?
What type of microbial replication is most common in prokaryotes?
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What is meant by generation time in microbial growth?
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How does generation time vary in microbial species?
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What is a characteristic of biofilms in healthcare settings?
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Which describes the growth condition of bacteria in nature compared to the laboratory?
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What enzyme converts hydrogen peroxide to water and oxygen?
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Which type of anaerobic microbe cannot eliminate reactive oxygen species (ROS)?
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Which microbial control method eliminates all bacteria, viruses, and endospores?
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How does refrigeration help in microbial management?
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What is the primary limitation of boiling as a sterilization method?
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What is the function of superoxide dismutase in aerobic microbes?
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Which type of anaerobic microbe can grow in the presence of oxygen but does not use it for metabolism?
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What is the primary use of a pressure steam sterilizer?
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What type of growth do bacteria exhibit as they divide by binary fission?
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Which phase occurs first in the distinct growth phases of bacteria?
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What happens to enzymatic reactions at low temperatures?
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What is the term for the highest temperature that supports microbial growth?
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Which group of microbes thrives in acidic conditions, such as pH 1?
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What characteristic is true about halophiles?
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Which type of microbe is predominantly associated with most pathogens?
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How do most pathogens' environments differ from others in terms of oxygen availability?
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What is a common consequence of high temperatures on bacterial cells?
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What strategy do halophiles use to thrive in high-salt environments?
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Which method can eliminate pathogens and reduce harmless microbes in milk?
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What is an example of dry heat sterilization?
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What type of radiation is characterized by shorter wavelengths and higher energy?
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What type of germs can be removed using HEPA filters?
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What do microbiocidal germicides do?
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What is the optimal concentration of alcohols used for disinfection?
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What characteristic of Mycobacterium species makes them more resistant to control methods?
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What is the most effective method for eliminating endospores?
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Which type of detergent is known for having both hydrophilic and hydrophobic parts?
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What factor is NOT commonly considered when selecting a germicide?
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Study Notes
Fundamentals of Microbial Growth (Replication)
- Microbes show dynamic and complex growth in nature, and more distinct growth stages in the laboratory.
- Microbial growth is cell division that produces new (daughter) cells and increases the total cell population.
- Most of our knowledge comes from studying species that can be cultivated in the laboratory.
Bacterial Replication
- In the laboratory, bacteria are usually grown as pure cultures.
- Environmental factors play a significant role in the life, metabolism, and structure of bacteria.
- Biofilms are communities of cells that communicate and collaborate to survive.
- Biofilms are a major concern in healthcare settings as they contribute to persistent infections.
Biofilms
- Biofilms are made up of bacteria encased in an extracellular matrix that adheres to surfaces.
- Medical devices like catheters and heart valves are potential havens for biofilms.
Bacterial Replication
- Binary Fission:
- Occurs in most prokaryotes.
- Asexual process that divides a single cell into two cells.
- Determines the arrangement of bacteria (e.g., Staph, strep, tetrads, singles, etc.)
- Can change over time.
Generation Time
- Generation time is the time it takes for a cell to divide.
- Times are diverse, ranging from about 15 minutes to 24 hours.
- Depends on the species and environmental conditions.
- The generation time impacts how fast a microbial population increases.
- Many common bacteria have generation times less than an hour (e.g., E. coli: 20 minutes).
- Some bacteria have fairly slow generation times (e.g., Mycobacterium tuberculosis: 15–20 hours).
- As bacteria divide by binary fission, they exhibit exponential growth.
Bacterial Growth Phases
- In the laboratory, bacteria are isolated and grown in closed pure batch cultures.
- Bacteria undergo distinct growth phases that can be detected by counting the number of viable cells.
Bacterial Growth Phases
- Lag Phase: Delay that occurs while cells adjust to their new environment.
- Log Phase: Period of rapid exponential growth.
- Stationary Phase: Nutrients are depleted, waste accumulates, population growth rate levels off.
- Death Phase: Cells begin to die at an exponential rate due to waste buildup and decreasing nutrients. A small number of cells survive by adapting to the waste and feeding off dead cells.
Prokaryotic Growth Requirements
- Prokaryotes adapt to various growth conditions.
- All microbes find a niche by adapting to specific conditions such as temperature, pH, salt concentrations, oxygen needs, and available nutrients.
Temperature
- Temperature is an important component of a microbe’s environment.
- Low temperature slows down enzymatic reactions.
- Increased temperature speeds up enzymatic reactions, which can increase growth rate.
- High temperatures denature cell proteins (kills the cell).
Temperature
- Three principal temperatures:
- Maximum temperature: highest temperature that supports growth.
- Minimum temperature: lowest temperature that supports growth.
- Optimum temperature: temperature where cellular growth is highest.
Temperature
- Can be used to classify microbes:
- Psychrophiles: Thrive between −20°C and 10°C.
- Psychrotrophs: Grow at about 0–30°C (associated with foodborne illness).
- Mesophiles: Grow best around 10°–50°C (associated with most pathogens).
- Thermophiles: Grow around 40–75°C (associated with compost piles and hot springs).
- Extreme thermophiles: Grow around 65–120°C.
pH
- Every microbe has a minimum, optimum, and maximum range of pH for growth.
- Acidophiles: Grow at pH 1 (or less) to pH 5. Live in areas such as sulfur hot springs and volcanic vents.
- Neutralophiles: Grow best in a pH range of 5–8. Make up the majority of microbes.
- Alkaliphiles: Grow in the basic pH range of 9–11. Associated with soda lakes.
High-Salt Conditions
- Halophiles: Thrive in high-salt environments. Tolerate up to 35%. Associated with the Dead Sea and the Great Salt Lake of Utah.
- Facultative halophiles: Tolerate higher salt but may not grow well (e.g., Staphylococcus aureus).
- Bacterial cytoplasm is mostly water. Halophiles must overcome the osmotic stress of a high-salt environment by keeping high concentrations of organic materials and ions in their cytoplasm.
Oxygen Requirements
- Many microbes on this planet live either without oxygen or with minimal oxygen.
- Oxygen levels are low beneath the soil or within silt deposits in lakes and oceans.
- Most pathogens thrive in low-oxygen environments within the host.
Oxygen Requirements
- Atmospheric Oxygen (O2) easily diffuses across cell plasma membranes.
- Inside the cell, some of the oxygen is converted into reactive oxygen species (ROS) (e.g., Hydrogen peroxide H2O2).
- ROS can rapidly damage proteins and DNA.
- Many microbes have evolved ways to detoxify ROS (e.g., aerobes).
- Superoxide dismutase converts reactive superoxide ions to hydrogen peroxide.
- Catalase converts the hydrogen peroxide to water and oxygen.
Oxygen Requirements
- Obligate aerobes: Require O2 for cellular processes.
- Obligate anaerobes: Do not use O2 in their metabolic processes. Can’t eliminate ROS. Tend to die in aerobic environments.
- Microaerophiles: Use only small amounts of O2. Live in low oxygen environments. Limits ROS.
Oxygen Requirements
- Aerotolerant anaerobes: Do not use O2 in their metabolic processes but can grow in its presence. Can manage ROS.
- Facultative anaerobes: Grow with and without O2. Switch between using aerobic respiration and fermentation.
Control Strategies
- Aim to reduce or eliminate microbial contamination.
- Microbial control measures occur in every area of our lives (e.g., water sanitation to hospital and restaurant cleaning standards).
- Decontamination removes or reduces microbial populations to render an object safe for handling.
- Sterilization eliminates all bacteria, viruses, and endospores.
- Disinfection reduces microbial numbers.
Temperature Changes
- Both cold and heat have important roles in controlling microbial growth.
- Refrigeration (4°C) and freezing (0°C) slow the growth of microbes.
- Most microbes are sensitive to heat. Heat can be used to achieve either sterilization or decontamination.
- An autoclave is a machine that applies steam heat along with pressure to sterilize.
Boiling
- Boiling water for 10 minutes eliminates most pathogenic bacteria, protozoans, and viruses.
- Endospores can withstand 1 hour of boiling, therefore it is not an efficient sterilization method.
Pasteurization
- Pasteurization is used to eliminate pathogens. (e.g., Listeria, Salmonella, E.coli)
- Application of moderate heat (below the liquid’s boiling point) eliminates pathogens and reduces harmless microbes that cause food spoilage.
- Developed by Louis Pasteur.
Dry Heat
- Incineration or hot-air ovens can also be used for sterilization or disinfection.
- Common examples of dry heat sterilization:
- Heating an inoculating loop to red hot in a Bunsen burner flame.
- Incinerating waste.
- Placing an object at 170°C (338°F) for 2 hours in a dry heat oven achieves sterilization.
Radiation
- Some physical decontamination methods involve radiation, or high-energy waves.
- Radiation can serve as a disinfection or sterilization tool depending on the protocol.
- Ionizing Radiation (e.g., gamma rays, X-rays): Short wavelength/high frequency, higher energy.
- Non-ionizing Radiation (e.g., UV rays): Longer wavelength/lower frequency, lower energy.
Filtration
- Large volumes of liquids or gasses can be passed through microbe-capturing filters.
- Filter pore sizes can even be made small enough to remove viruses.
- High-efficiency particulate air (HEPA) filters remove microbes and allergens from the air.
Germicides
- Chemical controls that limit microbes.
- Classified as microbiocidal (kill microbes) or microbiostatic (inhibit microbial growth).
- Two key classes:
- Disinfectants: used to treat inanimate objects.
- Antiseptics: applied to living tissue.
Alcohols
- Intermediate-level disinfectants.
- Denature proteins and attack lipid membranes.
- Examples: Ethanol and isopropanol.
- Optimal concentration is 60-90%.
- Used to disinfect small equipment (e.g., thermometers, scissors, stethoscopes).
Peroxygens
- High-level germicides at high concentrations.
- Can be used as antiseptics and disinfectants.
- Strong oxidizing properties.
- Examples: hydrogen peroxide, peracetic acid.
Detergents
- Cleaning agents.
- Amphipathic molecules (having both hydrophilic and hydrophobic parts).
- Remove water-soluble and water-insoluble substances.
- Some detergents damage the lipid envelope of certain viruses and the lipid membrane of certain bacterial cells.
Germicides
- Many factors must be considered to select an appropriate germicide:
- Item uses.
- Germicide properties.
- Germicide concentration and treatment times.
- Types of infectious agents being controlled.
- Presence of organic and inorganic matter.
- Impact of germicide residues on equipment use.
- Germicide compatibility.
Different Control Methods Work for Different Microbes
- Mycobacterium Control:
- Mycobacterium species cause tuberculosis and leprosy.
- Contain cell walls rich in waxy mycolic acids (making them harder to kill, more resistant).
- Spread by airborne droplets.
- Therefore, control measures target reducing airborne particles from infected individuals.
Different Control Methods Work for Different Microbes
- Endospore Control:
- Endospores are dormant structures.
- Can revert to growing (vegetative) cells once favorable growth conditions are restored.
- Endospores survive drying, radiation, boiling, chemicals, and heat treatments.
- Most effective way to ensure elimination of endospores is by autoclaving.
- Other methods include using glutaraldehyde vapor at high heat or sporicides.
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Description
Explore the fundamentals of microbial growth and the processes involved in bacterial replication. This quiz covers various growth stages of microbes, the significance of biofilms in healthcare, and the mechanisms of binary fission. Test your understanding of how bacteria thrive and replicate in laboratory and natural environments.
