CH. 5 Influence of Environmental Factors On, and Control of Microbial Growth Flashcards
How is oxygen utilized by bacteria?
They are a terminal electron acceptor in respiration
Enzymes can also react with oxygen to form reactive superoxide radicals (damaging to CNA, RNA, proteins, etc.)
Describe the different classifications of bacterial growth in response to different oxygen concentrations; what are the growth patterns?
- Aerobe (uses oxygen)
- Anaerobe (does not use oxygen; ferment or respire anaerobically)
- Facultative (can/cannot use oxygen; ferment or respire aerobically/anaerobically)
Growth patterns:
- If high oxygen (aerobes), located towards the top of the tube
- If low oxygen (microaerophilic), located towards the middle of the tube
- If no oxygen (anaerobic), located at the bottom of the tube
Explain the growth media used to detect these bacterial growth responses to oxygen
Use Thioglycolate Medium to then transfer the inoculum for the media to be seeded. Observe the growth of the media based on where it is located in the tube
How is oxygen damaging, even to aerobic microbes?
Because oxygen and its breakdown products are dangerously reactive
List and describe the types of microbial responses to oxygen or lack of oxygen.
Obligate Aerobes only grow with oxygen
Obligate Anaerobes only grow without oxygen (are killed by oxygen)
Facultative Anaerobes grows better with oxygen but can also thrive without it
Aerotolerant Anaerobes grows better without oxygen but can thrive in the presence of oxygen
Microaerophile requires little presence of oxygen
What are the protective mechanisms microbes have to minimize oxygen damage?
-Superoxide dismutase enzyme (to remove superoxide)
-Peroxidase and catalase enzymes (to remove hydrogen peroxide)
How are anaerobes cultured?
Special reducing agents (enzyme systems) eliminate dissolved oxygen can be added to liquid media, so anaerobes can then grow beneath the culture surface
Usage of an anaerobe jar where agar plates are placed into a sealed jar with a foil packet then the palladium packet hanging from the jar lid catalyzes a reaction to remove oxygen
In terms of controlling microbial growth, describe the differences between: sterilization, disinfection, antisepsis, and sanitation.
Sterilization - Destruction of all cells, viruses, spores
Disinfection - Reduction of pathogen numbers (for inanimate objects)
Antisepsis - Reduction of pathogen numbers (for living tissues)
Sanitation - Relates to hygienic practices (reduction in overall total microbial numbers)
How do bactericidal agents differ from bacteriostatic agents and bacteriolytic agents?
Bacteriostatic - Inhibits growth (NO killing of cells)
Bacteriocidal - Cells remain intact (Killing of cells)
Bacteriolytic - Cells are lysed/destroyed (Killing of cells)
What is the decimal reduction time, or D‐value?
Time for the agent to kill 90% of the bacteria population
What factors affect the D‐value of an antimicrobial agent? Why is death logarithmic?
Factors:
- Microbial load
- Agent quantity
- Exposure time
- Population composition
- Organic load
- Corrosiveness
- Stability
- Surface tension
Death is logarithmic because it occurs due to the accumulation of damage (varies within how fast damage accumulates)
Describe physical agents that control microbial growth and the mechanisms by which they act. Which is/are most effective in killing spores?
High temperature & pressure (autoclave:15 psi/121⁰C/15 min) *Effective in killing spores
Pasteurization (heating a specific food long enough to kill)
Cold (low temperatures to temper growth and preserve strains)
Filtration (using micropore filters)
Irradiation (used to sterilize food and nonbiological)
*UV rays (nonionizing radiation) cause mutation while X-rays (ionizing radiation) penetrate
List examples of common commercial disinfectants and briefly describe how they act on microbes. Do microbes generally become resistant to these agents? Why or why not?
Ex. ethanol, iodine, chlorine, and surfactants
They damage protein, lipids, and DNA
Microbes usually do not become resistant to these agents because disinfectants have multiple targets, making it harder for bacteria to mutate to become resistant
What are antibiotics? Where do they originate from? What do they target and how do they work? How does resistance to antibiotics compare to that of disinfectants?
Antibiotics are chemical compounds synthesized by one microbe to kill or stop the growth of other competing microbial species
They target protein synthesis, DNA replication, cell membranes, and enzyme reactions (only targeting a specific component of the microbe)
What conditions can alter the osmotic balance and inhibit bacterial growth?
Having incompatible solutes which disrupt the cell metabolism at high intracellular concentrations, disrupting the osmotic balance
