Microbiology: A Human Perspective: Chapter 4 - Exam II Flashcards

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Dynamics of Prokaryotic Growth
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Explain why microbial growth refers to a population rather than a cell in size.

If a bacterium has a generation time of 30 minutes, and you start with a 100 cells at a time 0, how many cells will you have in 30, 60, 90, and 120 minutes.

Why would placing potato salad in a cooler affect cell growth?

-After a cell has increased in size and doubled all of its parts divides.

-200, 400, 800, 1600

-It will grow at ideal room temperature.


Describe Binary fission and how it relates to generation time.

When a cell has increased in size and doubled all of its parts, it divides. The increase in cell numbers is exponential. The time it takes for a population to double in number is the generation time.


Describe a Biofilm and give one positive and one negative impact that biofilms have on humans.

Biofilm is a polysaccharide-encased community of microorganisms.

Positive: Bioremediation effors use bacteria to degrade harmful chemicals, are enhanced by biofilms.

Negative: It is estimated that 65% of human bacterial infections involve biofilms.


Explain why bacteria grow naturally in mixed communities sometimes cannot yet be grown in pure culture.

Metabolic wastes of one species may serve as a nutrient for another. The conditions in these close associations are difficult to reproduce in the lab.


Give three examples of biofilms.

Describe a situation in which the activities of one species benefit another.

Why would bacteria in a biofilm be more resistant to harmful chemicals?

-Kitchen drain gunk, dental plaque, and slime on rocks in the stream.

- A Microbe found in the mouth can consume O2 during their metabolism, creating a microenvironments that lack O2 which can benefit a different organism.

-The structure of biofilm shields the microbes growing within it, and bacteria in a biofilm may be hundreds of times more resistant to disinfectants than are their planktonic counterparts.


Describe how the Streak-plate method is used to obtain a pure culture, and how the resulting culture can be stored.

A sterilized inoculating loop (1) is dipped into a culture (2) and is then lightly drawn several times across an agar plate. (3) The loop is sterilized again, (4) and a new series of streaks is made at an angle to the first set. (5) The loop is sterilzed a final time, (6) and another set of parallel streaks is made. (7) The successive streaks dilute the concentration of cells. By the third set of streaks, cells should be separated enough so that isolated colonies develop after incubation.

Once a pure culture has been created it can be maintained as a stock culture. Often stock cultures are stored in the refrigerator on an agar slant.


What properties of agar make it ideal for use in bacteriological media?

How does the streak-plate method separate individual cells?

What might be a reason that medically significant bacteria can be grown in pure culture more often than environmental organisms?

-Agar is undegradeable by bacteria, could be sterilized at high temperatures, the temperature range of the agar allows it to add nutrients at a low temperature (solid below 45degrees), stays solid at ideal temparture for bacteria (which is around 37 degrees), its clear and transluscent so easier to see bacteria.

-We dilute it so it gets less and less everytime we streak it.

-Because medically significant bacteria surivive in environments similar to humans.


Describe the five distinct stages of a growth curve, and compare this closed system to colony growth and continuous culture.

(1) Lag phase -(cell preps to divide binary fission), (2) Exponential Phase (Log phase)-early log produces primary metabolites and the later log phase produces secondary metabolites), (3) Stationary Phase (cells grow to death is equal), (4) Death Phase (the number dying is more than growth), (5) Phase of Prolonged Decline (slower gradual decrease of living cells, they are the ones that adapt to the harsh environment).

Closed system are not renewed, nor are waste products removed. To maintain cells in a state of continuous growth, nutrients must be contiuously added and waste products removed.


Explain the difference between the two stages of the exponential phase.

In early log phase the cells produce primary metabolites (amino acids and proteins) directed toward cell growth.

During the late log phase the cells begin synthesizing different enzymes and other proteins which produce secondary metabolites (antibiotics).


Describe how a chemostat keeps a culture in a continuous stage of growth.

A chemostat continually drips fresh medium into a liquid culture contained in a growth chamber. With each drop that enters, an equivalent volume, containing cells, wastes, spent medium, leaves through an outlet. A constant cell density and generation of log phase cells can be maintained.


List the descriptive terms that express a prokaryote's requirements for temperature.

Psychrophile - Arctic temp; -5° and 15°C

Psychrotroph - Causes food spoilage; 20°C and 30°C

Mesophile - Disease-causing bacteria; 25°C and 45°C

Thermophile - Hot springs and compost heaps; 45°C and 70°C

Hyperthermophile - Archaea; >70°C


List the descriptive terms that express a prokaryote's requirements for oxygen.

Obligate aerobe - requires O2

Obligate anaerobe - cannot multiply in the presence of O2

Facultative anaerobe - Grows best if O2 is present, but can grow without.

Facultative means it is flexible, can use aerobic respiration or fermentation or anaerobic respiration.

Microaerophile - Requires small amounts of O2 but higher concentrations are inhibitory. Gastric and duodenal ulcers.

Aertolerant anaerobe (obligate fermentor) - Indifferent to O2. i.e.Strep throat.


List the descriptive terms that express a prokaryote's requirements for pH and water availability.

Neutrophile - Multiplies in the range of pH 5 to 8

Acidophile - Grows optimally at a pH below 5.5

Alkalophile - Grows optimally at a pH above 8.5

Osmotolerant - Can grow in relatively high salt solutions, up to approximately 10% NaCL.

Halophile - Requires high levels of sodium chloride.


Describe four environmental factors that influence the growth of bacteria?

-Temperature - Thermostabilty appears to be due to protein structure.

Oxygen (O2) Availability - Oxygen requirement/tolerance reflects the organism's energy-converting mechanisms (aerobic respiration, anaerobic respiration, and fermentation) and its ability to detoxify O2 derivatives.

pH - Prokaryotes that live in pH extremes appear to maintain a near neutral internal pH by pumping protons out of or into the cell.

Water availability - Prokaryotes that can grow in high solute solutions maintain the availabillity of water in the cell by increasing their internal solute concentration.


List the catergories into which bacteria can be classified according to their requirements for oxygen.

Obligate aerobe: Catalase: 2H2O -> 2H2O + O2; Superoxide dismutase: 2O2 - + 2H+ -> O2 + H2O2

Facultative anaerobe: Catalase, superoxide dismutase

Obligate anaerobe: Neither catalase nor superoxide dismutase in most

Microaerophile: Small amounts of catalase and superoxide dismutase

Aerotolerant: Superoxide dismutase


Why would small organic compounds affect the water content?

- If the solute concentration is higher outside the cell, water moves out. The dehydrated cytoplasm shrinks from the cell wall, a process called plasmolysis.


Give an example of a bacterium that is Fastitious (Microorganisms displaying a wide spectrum in their growth factor requirements.)

Neisseria require at least 40 additional ingredients, including 7 vitamins and all of the 20 amino acids.

Lactobacillus is grown in a medium that lacks a specific viamin, but supplemented with a food product. The growth amount of the bacteria is used to determine the quantity of specific vitamins in a food product.


Define the term Photoautotroph, Chemolithoautotroph, Photoheterotroph, and Chemoorganoheterotroph.

Photoautotroph - Plants, algae, and photosynthetic bacteria; energy source: sunlight, Carbon source: CO2

Photoheterotroph - Facultative capabilities; energy source: sunlight, Carbon source: Organic compounds

Chemolithoautotroph - Mamilian cells, fungi, bacteria metabolizing organic compounds; energy source: inorganic chemicals, Carbon source: CO2

Chemoorganoheterotroph - most similar to humans and animals; Energy source: Organic compounds, Carbon Source: Organic compounds


Compare and contrast complex media, chemically defined media, selective media, and differential media.

Complex medium - variety of ingredients, tasty soup for microbes

Chemically defined media - precise amounts of pure chemicals

Selective media - Thayer-Martin agar, MacConkey agar; use to detect or isolate an organism by adding complex media.

Differential media - MacConkey agar; contain substance that certain bacteria change in a recognizable way. Adding solution that will cause a bacteria to react.


Organisms require a source of major and trace elements. Heterotrophs use an organic carbon source, and autotrophs use CO2. Phototrophs harvest the energy of sunlight, and chemotrophs obtain energy by degrading chemicals.

List the major elements other than carbon required for growth of bacteria.

Oxygen and hydrogen - component of cellular constituents (amino acids, lipids, nucleic acids, and sugars)

Nitrogen - component of amino acids and nucleic acids

Sulfur - component of some amino acids

Phosphorus - component of nucleic acids, membrane, and lipids

Potassium, magnesium, and calcium - required for the functioning of certain enzymes, additional functions as well.

Iron - part of certain enzymes.


What is the carbon source of a photoautotroph? Of a chemoautotroph?

Why would human-made materials (such as plastics) be degrade only slowly or not at all?

Photoautotroph's and Chemoautotroph's require CO2

Because human-made materials are not ideal sources of energy for organisms.


Explain how the correct atmospheric conditions are provided to cultivate obligate aerobes, capnophiles, microaerophiles, and obligate anaerobes.

Obligate aerobes - tubes or flasks containing media are shaken providing maximum aeration.

Capnophiles - candle jar, requires increased CO2 along with approximately 15% oxygen.

Microaerophiles - gastight jar, require O2 concentration less than canophiles.

Obligate anaerobes - airtight anaerobe jar, anaerobic chamber, cells killed when exposed to O2 for even a short time.


Describe the purpose of an enrichment culture.

Provides conditions in a broth that perferentially enhance the growth of one particular species in a mixed population.

This is helpful in isolating an organism from natural sources when the bacterium of interest is present in small numbers.


Distinguish between a selective medium and a differential medium.

In selective enrichment the medium and incubation conditions favor the growth of the desired species over other bacteria in the same sample.

Where as differential media contains a substance that certain bacteria change in a recognizable way.


Describe two methods used to create anaerobic conditions.

Would bacteria that cannot utilize lactose be able to grow on MacConkey agar?

Anaerobe Jar - the hydrogen released from the generator combines with any O2 to form water, therby producing an anaerobic environment.

Anaerobic chamber - enclosed compartment can be maintained as an anaerobic environment.

MacConkey Agar - will expose Lactose-negative colonies as tan or colorless.


Compare and contrast direct cell counts, viable cell counts, measuring biomass, and detecting cell products to measure bacterial growth.

Direct cell counts - used to determine total number of cells; count includes living and dead cells.

Viable cell counts - Used to determine the number of viable bacteria in a smaple, but that number only includes those that cna grow in given conditions. Requires an incubation period of approximately 24 hours or longer. Selective and differential media can be used to enumerate specific species of bacteria.

Measuring biomass - Biomass cna be correlated to cell number.

Measuring cell products - Methods are rapid but results must be correlated to cell number. Frequently used to detect growth, but not routinely used for quantitation.


Why is an MPN an estimate rather than an accurate number?

Why would a direct microscope count yield a higher number than a pour plate if a sample of seawater was examined by both methods?

The nitrogen in microorganisms will typically be present in what molecules?

MPN is a statistical assay of cell numbers based on the theory of probability.