microbiology exam 2 chapter 4 pt 2 Flashcards
How do microorganisms combat low water activity in their environment?
Microorganisms combat low water activity by:
Pumping inorganic ions from the environment into the cell.
Synthesizing or concentrating organic solutes.
What are compatible solutes?
Compatible solutes are compounds used by cells to counteract low water activity in their surroundings, helping maintain cellular function in environments with low water availability.
What is the role of oxygen in microbial growth?
Microorganisms use oxygen for aerobic respiration as a terminal electron acceptor.
What is aerobic respiration in microorganisms?
It’s the process where oxygen is used in the electron transport chain to produce energy.
What are strict (obligate) aerobes?
Organisms that can only grow in oxygen.
what are microaerophiles?
Organisms that grow only at lower oxygen levels.
What are strict (obligate) anaerobes?
Organisms that die in the presence of oxygen.
What are aerotolerant anaerobes?
Organisms that grow in oxygen but use fermentation for energy.
What are facultative anaerobes?
Organisms that can grow with or without oxygen, using both fermentation and respiration.
How does a reducing agent like thioglycolate work in oxygen-removal?
It reacts with oxygen, allowing oxygen to only penetrate the top of the tube
What is an anaerobe jar used for?
It removes O2 through a reaction catalyzed by palladium.
How does an anaerobic chamber work?
Oxygen is removed by vacuum and replaced with N2 and CO2.
What are capnophiles?
Microbes that require high CO2 conditions.
How can CO2 conditions be created for culturing capnophiles?
Using a CO2 packet or candle jar.
What is sterilization?
Killing of all living organisms.
What does disinfection refer to?
Killing or removal of pathogens from inanimate objects.
What is antisepsis?
Killing or removal of pathogens from the surface of living tissues.
What does sanitation involve?
Reducing the microbial population to safe levels
What is the D-value?
The D-value is the length of time it takes an agent or condition to kill 90% of the population
How do microbes die?
Microbes die according to a negative exponential curve, where cell numbers are reduced in equal fractions at constant intervals.
How does high temperature kill microbes?
High temperature denatures macromolecules.
What is the effect of boiling water on microbes?
Boiling water (100°C) kills most cells but does not kill spores and thermophiles.
How are spores and thermophiles typically killed?
Spores and thermophiles usually require a combination of high pressure and temperature, like in a steam autoclave (121°C at 15 psi for 20 minutes).
t/f: Moist heat is more effective than dry heat.
true
What is an autoclave and how does it kill microbes?
ealed device that uses steam
under pressure. Allows temperature of water to get above 100ºC
what kills microbes in autoclaving
it’s not the pressure, but the high temperature,
that kills the microbes
What are the different methods of pasteurization and their temperatures?
LTLT (Low Temperature/Long Time): 63ºC for 30 minutes
HTST (High Temperature/Short Time): 72ºC for 15 seconds
What bacteria are killed by pasteurization?
Pasteurization kills most pathogenic bacteria, including Mycobacterium tuberculosis, Salmonella, and Listeria, but does not kill all microbes (e.g., spores) or some heat-resistant bacteria.
How does cold temperature affect microbial growth?
Cold temperatures slow microbial growth and preserve strains, which is useful for storing cultures and food preservation.
What are methods for long-term storage of cultures?
Placing solutions in glycerol at –70ºC
Lyophilization or freeze-drying
refrigeration temperatures are used for food preservation whats the temp range
4C-8C
What is the function of micropore filters in filtration?
Micropore filters with pore sizes of 0.2 µm can remove microbial cells, but not viruses, from solutions.
How can samples be processed through micropore filters?
Samples from 1 ml to several liters can be drawn through a membrane filter by vacuum or forced through it using a syringe.
How can air be sterilized, and what is the role of HEPA filters?
Air can be sterilized by filtration using laminar flow biological safety cabinets that force air through HEPA filters. These filters remove >99.9% of airborne particulate material 0.3 μm in size or larger.
What is the effect of ultraviolet (UV) light on microbes?
UV light sterilizes surfaces but has poor penetrating power.
How do gamma rays, electron beams, and X-rays kill microbes?
These rays have high penetrating power and are used for sterilizing food and heat-sensitive items.
What factors influence the efficacy of a chemical agent?
Presence of organic matter
Types of organisms present
Corrosiveness
Stability, odor, and surface tension
How are chemical agents evaluated for effectiveness?
Chemical agents are evaluated by in-use tests.
What are some common commercial disinfectants and antiseptics?
Ethanol
Iodine (Wescodyne, Betadine)
Chlorine
Ethylene oxide (gas sterilant)
How do commercial disinfectants and antiseptics work?
They damage proteins, lipids, and/or DNA to reduce or eliminate microbial content.
How can bacteria develop resistance to disinfectants?
Altering fatty acid synthesis proteins (targeted by triclosan)
Producing multidrug efflux pumps
Forming multispecies biofilms for collaborative protection
What are antibiotics?
Chemical compounds synthesized by one microbe that kill or inhibit the growth of other microbes.
How does penicillin work?
Mimics part of the bacterial cell wall, preventing cell wall formation, and is bactericidal.
What other targets do antibiotics affect?
protein synthesis
DNA replication
Cell membranes
