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Terms in this set (14)
Classify microbes into five groups on the basis of preferred temp. range. Distinguish between graphs that depict growth rates in response to temp.
-psychrophiles (cold loving) 0-15 degrees C
-psychotrophs (able to grow in cold temps but not as low as psychrophiles-food spoilagein fridge or freezer) 20-30 degrees C
-mesophiles (moderate-temp-loving) 20-40 degrees C =most human pathogens
-thermophiles (heat-loving) 45-80 degrees C =not very common
Explain the importance of osmotic pressure to microbial growth. Understand how hypertonic and hypotonic solutions affect cells.
Osmotic Pressure- Cells require waterfor growth and are made up of 80-90%water
Provide a use for each of the four elements (carbon, nitrogen, sulfur, and phosphorus) needed in for microbial growth. Why are trace elements important?
Carbon: Structural organic molecules, energy source.
Nitrogen: is needed for protein and nucleic acid synthesis.
Sulfur: is used to synthesize sulfur-containing amino-acids and vitamins such as thiamine and biotin.
Phosphorus: needed for the synthesis of ATP.
Trace elements: Inorganic elements required in small amounts
Explain how microbes are classified on the basis of oxygen requirements. Distinguish between graphs that depict growth rates in response to oxygen requirements.
Obligate aerobe: dependent on oxygen for growth.
-Facultative anaerobes: do not require oxygen, but grow faster with it present. Obligate anaerobe: do not grow under oxygen conditions.
-Aerotolerant: cannot use oxygen - but tolerates it.
-Microaerophiles: require lower concentrations of oxygen.
What enzymes are used by aerobes and facultative anaerobes to avoid damage by toxic forms of oxygen.
* SUPEROXIDE DISMUTASE.
*CATALASE or PEROXIDASE.
-Hydroxyl radical: Most reactive of the toxic forms of oxygen.
Describe the formation of biofilms and their potential for causing infection
Biofilms are a natural structure formed by microbes in the environment. They stick to healthy surfaces and will prevent nutrients to go through to keep it healthy. It will block any immune response and antibiotics because of the slime wall. causing problems with dental plaque, catheters, and other indwelling devices. Pseudomonas spp. is an example that forms biofilms.
Describe the safety protections for the four biosafety levels
BSL-1: no special precautions
BSL-2: lab coat, gloves, eye protection
BSL-3: biosafety cabinets to prevent airborne transmission
BSL-4: sealed, negative pressure
-Exhaust air is filtered twice
Distinguish between chemically defined and complex media. What is enrichment media?
Chemically defined media: Exact chemical composition is known
Complex media: Composition of nutrients varies; composed of extracts of yeasts, meat, or plants
Enrichment Media - Encourages growth of desired microbe
Define colony and describe how pure cultures can be isolated by streak plates.
colony: population of cells arising from a single cell, spore, or from a group of attached cells.
-Using the streak plate method, it allows the bacteria that are rubbed off last, to grow into colonies because there are a small enough number of organisms present.
Explain how microbes are preserved by deep-freezing & lyophilization (freeze-drying)
Deep-freezing: -50°to -95°C
Lyophilization (freeze-drying): Frozen (-54° to -72°C) and dehydrated in a vacuum
Define bacterial growth. Describe binary fission?
bacterial growth refers to an increase in bacterial numbers
Binary fission (cell splitting) - normal method of bacterial reproduction
Compare the phases of microbial growth and understand how they are represented in a graph
LAG PHASE- period of little or no cell division, can last for 1 hour or several days; however, cells are not dormant. undergoing intense metabolic activity involving synthesis of enzymes and various molecules
LOG PHASE- cells begin to divide and enter a period of growth. reproduction is active during this period and generation time reaches a constant minimum. since constant, it is a straight line. cells are most active metabolically and is preferred for industrial purposes where a produce needs to be produced
STATIONARY PHASE- period of equilibrium. growth rate slows, microbial deaths balances the number of new cells and the population stabilizes
DEATH PHASE- the number of deaths eventually exceeds to number of new cells formed. phase continues until population is diminished to a tiny fraction of cells or until it dies out completely.
Explain four direct methods of measuring cell growth.
PLATE COUNTS: most frequently used method of measuring bacterial population. advantage- measures the number of viable cells. disadvantage- takes some time, usually 24 hours or more for visible colonies to form. reported as colony-forming units (CFU) count plates with 30-300 colonies
SERIAL DILUTIONS: original inoculum is diluted several times.
FILTRATION: at least 100 ml of water are passed through a thin membrane filter whose pores are too small to allow bacteria to pass. the bacteria are filtered out and retained on the surface of the filer. the filter is then transferred to a Petri dish containing a pad soaked in liquid nutrient medium. applied to detection and enumeration of coliform bacteria.
SPREAD PLATE METHOD: inoculate plate containing solid medium, spread inoculum over surface evenly, colonies grow on surface of medium
Differentiate between direct and indirect methods of measuring cell growth.
DIRECT METHODS(plate counts, filtration, MPN, direct microscopic count)- measure the number of cells or total mass
INDIRECT METHODS( turbidity, metabolic activity, dry weight)- it is not always necessary to count cells to estimate their numbers (looking at the medium, differences, changes)
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