Ch. 6 Microbio Study Questions
What enzymes are used by aerobes and facultative anaerobes to avoid damage by toxic forms of oxygen.
-SUPEROXIDE (O2-) free radicals are a toxic byproduct of aerobic respiration. Aerobes have an enzyme called SOD (superoxide dismutase) that converts superoxide free radicals into water and hydrogen peroxide. -PEROXIDE ANION (O2^2-): a byproduct of the SOD reaction - is also toxic, so we have catalase to neutralize it -The enzyme CATALASE converts peroxide anion into into water and oxygen, and/or the enzyme peroxidase converts it into water. -HYDROXYL RADICAL (OH-)
Explain the importance of osmotic pressure to microbial growth. Understand how hypertonic and hypotonic solutions affect cells.
-growth of cell is inhibited if high concentration occurs -high salt/sugar concentrations draw water out any microbial cells that are present & thus prevent their growth REVIEW: HYPERtonic: -higher concentration of solute to solution -flows OUT of cells -shrinks/shrivels HYPOtonic: -lower concentration of solute to solution -flows INTO cells -swells/bursts
Explain four direct methods of measuring cell growth.
1) PLATE COUNT: -Count colonies on plates that have 30 to 300 colonies (CFUs) -Counts are performed on bacteria mixed into a dish with agar (pour plate method) or spread on the surface of a plate (spread plate method) 2) FILTRATION: -Used with smaller number of bacteria -Filter is transferred to agar medium and grows as colonies on the surface 3) DIRECT MICROSCOPIC COUNT: -Average number of bacteria per viewing field is calculated -Formula: # of bacteria/ml=# of cells counted(divided by) volume of area counted 4)POUR PLATE METHOD 5) SPREAD PLATE METHOD
Define bacterial growth. Describe binary fission?
BACTERIAL GROWTH-proliferation of bacteria into two daughter cells, in a process called binary fission BINARY FISSION -definition: (cell splitting) - normal method of bacterial reproduction -budding -conidiospores -fragmentation of filaments
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
How is budding different from binary fission?
Binary fission occurs when a parent cell splits into two identical daughter cells of the same size. Budding occurs when a parent cell forms a bubble-like bud. The bud stays attached to the parent cell while it grows and develops.
Describe the formation of biofilms and their potential for causing infection.
Biofilms -Definition: are a natural structure formed by microbes in the environment. -What do they do?: They stick to healthy surfaces and will prevent nutrients to go through to keep it healthy. -Potential for causing infection?: 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.
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: needed for protein and nucleic-acid synthesis SULFUR: used to synthesize sulfur-containing-amino-acids and vitamins such as thiamine & biotin PHOSPHORUS: needed for the synthesis of ATP Trace elements function primarily as catalyst in enzyme systems
Define colony and describe how pure cultures can be isolated by streak plates.
Colony-a 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.
Distinguish between chemically defined and complex media. What is enrichment media?
Cultural Media CHEMICALLY DEFINED MEDIA: (synthetic) medium is one in which the exact chemical composition is known COMPLEX MEDIA: (undefined) medium is one in which the exact chemical constitution of the medium is known Selective and Differential Media ENRICHMENT MEDIA: encourages growth of desired microbe
Explain how microbes are preserved by deep-freezing & lyophilization (freeze-drying)
DEEP-FREEZING -process in which a pure culture of microbes is placed in a suspending liquid and quick-frozen at temperatures ranging from -50-(-95) LYOPHILIZATION -a.k.a freeze-drying -a suspension of microbes is quickly frozen at temperatures ranging from -50 -(-72) and the water is removed by a high vacuum, while under the vacuum, the container is sealed by melting the glass with a high-temperature torch -FROZEN AND THEN DEHYDRATED IN A VACUUM
Differentiate between direct and indirect methods of measuring cell growth.
DIRECT- measurement of the growth of microbial populations through measuring cell numbers, measuring the population's total mass (direct counts on small samples) INDIRECT- Not always necessary to count microbial cells to estimate their numbers
How is microbial growth impeded when high concentrations of sugar or salt are used to preserve food?
Like salt water also has an osmotic effect i.e. when foods are placed in a concentrated sugar solution water is drawn out of the cells of foods and microorganisms so that microorganisms can no longer survive.
Compare the phases of microbial growth and understand how they are represented in a graph.
MICROBIAL GROWTH refers to the growth of a population (or an increase in the number of cells) Growth Curve - exponentially increasing populations, plotted logarithmically (dashed line) and arithmetically (solid line)
Is a colony formed as a result of streaking a plate always derived from a single bacterium? Why or why not?
No, there are other organisms that could contaminate it-Ex: staph forms clumps, so how can you be sure that there aren't other strains in that clump
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 OBLIGATE ANAEROBE: do not grow under oxygen conditions AEROTOLERANT: cannot use oxygen but tolerates it MICROAEROPHILES: require lower concentrations of oxygen
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 celsius PSYCHROTROPHS: 20-30 celsius MESOPHILES: (moderate temp loving) 25-40 celsius THERMOPHILES: 50-60 celsius HYPERTHERMOPHILES: 80+ celsius
What are the oxygen requirements, for obligate aerobes, facultative anaerobes, and obligate anaerobes?
Same answer as number 4
Given a shallow pan and a deep pot with the same volume, which would cool faster? Why?
Shallow, more surface area would allow the pot to get through the danger zone quicker
What are the temperature ranges of psychrophiles, psychrotrophs, mesophiles,and thermophiles? How would human pathogens and food spoilage microorganisms be characterized?
TEMP RANGES -Psychrophiles: 0-15 celsius -Psychrotrophs: 20-30 celsius -Mesophiles: (moderate temp loving) 25-40 celsius -Thermophiles: (heat loving) 50-60 celsius Psychrotrophs can cause food spoilage Mesophiles relate to common food spoilage and disease organisms. 37°C optimum temp for human pathogenic bacteria.
If a single bacterium reproduces every 30 minutes, how many would there be in 2 hours?
Use the formula 2^n . So bacteria divides every 30 mins and there are four times 30 minutes in 2 hours so take n=4 So 2^4 = 2*2*2*2 = 16 Hence there will be 16 bacteria after 2 hours.
Why is the prevention of biofilms important in a healthcare environment?
Using salt was an easy thing to do for a primitive civilization and they noted no bacterial growth.
Are bacteria capable of growing at a high osmotic pressure likely to be capable of growing in the mucus found in nostrils?
Yes because staphylococcus aureus found in the nasal passage have high tolerance to sodium chloride.
If 95 colonies grow on a 1:10,000 dilution plate, how many bacteria were in the original sample?
unknown
Why is direct microscopic counting an advantage over plate counts when used in estimating the bacterial population in dairy products?
unknown
Why is turbidity more useful in measuring contamination of liquids by large numbers, rather than small numbers, of bacteria?
unknown
