Download Microbiology Extra Credit asg

Shaylyn Robison
Microbiology 2060
MW 5:30-7:15pm
Summer 2010
Extra Credit Questions Chapters 1, 2, 3 and 5
Chapter 1 (pages 3, 8, 12, 13, & 15)
Page 3
1.) Microbiology is the study of small organisms, such as bacteria and viruses, which cannot be
clearly seen with the naked eye. Various types of microscopes and staining processes are used to
observe and study microorganisms.
2.) Procaryotic cells lack a membranous nucleus; they have a nucleiod instead. Eukaryotic cells
are typically bigger and have a more complex morphology than Procaryotic cells.
3.) The five-kingdom systems classifies organisms into five kingdoms: Protista, Fungi, Plantae,
Animalia, and Monera. From there, the organisms are then organized into phyla, then class,
order, families, genus, and species. The three-domain system classifies organisms into three
domains: Bacteria, Eucaraya and Arcahea. Before the three-domain system was used, Bacteria
and Arcahea were classified into the Monera kingdom of the five-kingdom system. The threedomain system is shown as a better classification system by Carl Woese’s research of RNA.
Viruses are not included in either system because they replicate different then prokaryotes and
eukaryotes. They need a host cell in order to replicate. Viruses are classified separately because
they do not meet the same criteria as needed for the other classifying systems.
1.) By observing microorganisms, we can learn more about diseases, and how they affect us and
other organisms. We can also learn how microorganisms function by observing them
microscopically, which in turn can help us fight off the ones that may be harmful.
2.) Isolating and culturing microorganisms can help us determine what factors in their
environment contributes to their development and also provides a bigger, purer sample of
microbes. By isolation microorganisms, we can also support or disprove theories that involve
organisms, such as the Spontaneous Generation Theory.
Page 8
1.) Louis Pasteur disproved the Theory of Spontaneous Generation Theory by filtering air
through cotton pieces and observing microorganisms after the cotton was placed in a sterile
medium. He also found a way to preserve solutions, a process now called pasteurization. Pasteur
would heat solutions in open flasks and moved them so that the solution would flow through the
curves of the flask. He would then boil the solution and allowed them to cool. There would be no
growth in the solution in the open ended flask because he observed the microbes would be
trapped on the walls of the curved walls of the flask. John Tyndall also helped disprove the
Theory of Spontaneous Generation by proving that dust carried germs. He demonstrated that if
dust was absent broth was sterile even if exposed to air. He also found evidence of bacteria that
were resistant to heat.
2.) Belief in spontaneous generation was an obstacle to the development of microbiology as a
scientific discipline because people believed that things such as disease and maggots appeared
out of nothing. They did not believe microorganism exist partly because they could not see them.
Disproving spontaneous generation led to discoveries of disease-causing microorganisms and
eventually to ways of controlling them.
Page 12
1.) Pasteur contributed to the germ theory of disease when he disproved the spontaneous generation
theory and when he developed pasteurization. Pasteur investigated a diseased, disrupted silk industry
and discovered it was due to a parasite. John Lister developed a antiseptic system to prevent
microorganisms from entering wounds during surgery. This system in turn provided evidence of
microorganisms in diseases. Robert Koch published criteria for proving that there is a relationship
between a specific microorganism and a specific disease. His criteria, known as Koch’s Postulates, is
used to determine different diseases in hand with their microorganisms that cause them, and can lead
to a way to prevent the diseases.
2.) Koch developed a way grow bacteria on culture media. The first media used was gelatin.
3.) Koch’s postulates are a way to establish the link between a microorganism and a disease. Pure
culture: only one type of organism in a culture that is to be studied. Pure cultures are important to
Koch’s postulates because if there were two or more organisms on the culture, you wouldn’t know
which one caused the disease. Pure cultures help isolate and discover which microorganism is
causing the disease.
4.) Microbiology could have developed more slowly if Fannie Hess had not suggested agar. Trial
and error usually produce results but suggestions such as Fannie’s help speed the discovery process
along.
5.) Koch’s Postulates: 1. Microorganism must be present in every case of the diseases but absent
from the healthy. 2. Suspected microorganisms must be isolated and grown in pure culture. 3. The
same disease must result when the microorganism is introduced to a healthy host. 4. The same
microorganism must be isolated again from the diseased host. Koch’s postulates are important
because they are guidelines that are key in narrowing down suspected microorganisms that can a
specific disease.
6.) People who are carriers for chronic disease, but don’t show symptoms, impact Koch’s postulates
because the disease cannot be observed in the host. The evidence for the disease-causing
microorganism in the carrier is limited because it does not cause symptoms. It would be hard to
prove that it exists. To modify the postulates, it could be said that if the microorganism is present in
a carrier, and the same microorganism can be isolated from a diseased person, then the
microorganism present in both parties causes the disease.
7.) The scientific method is a step by step process that is generally used by all scientists. It consists
of hypothesizes, theories, experimenting, observing and analyzing information and usually more
testing. A hypothesis is a statement or explanation pertaining to a scientific observation that can be
tested. A theory is a well-established statement or explanation that is supported by evidence. A
theory is developed after a hypothesis is tested multiple times.
8.) Emil von Behring discovered a way to treat against a toxin produced by diphtheria bacillus; the
treatment is known as tetanus and its discovery was important to the development of immunology.
Elie Metchnikoff discovered that certain cells in the blood could eat or engulf bacteria. This
engulfment is known as phagocytosis.
1.) Pasteur studied the effect of microorganisms on fermenting drinks such as beer and wine. He
discovered the living conditions of certain microorganisms such as some are anaerobic and others
produced lactic acid rather than ethanol. His observations led to better was to preserve food and
drinks.
2.) Winogradsky and Beijernick contributed to the study of microbial ecology by developing new
culture techniques and selective media. Winogradsky studied the decomposition of cellulose and
isolated anaerobic soil bacteria. He also discovered soil bacteria could oxidize such elements as iron,
sulfur and ammonia to acquire energy. Beijernick isolated Azotobacter, Rhizobium and sulfatereducing bacteria.
Page 13
3.) Leeuwenhoek was one of the first scientists to see bacteria and observe them. Pasteur and Koch
contributed more to the field of Microbiology but they came after Leeuwenhoek. I think
Leeuwenhoek is the Father of Microbiology, but Pasteur and Koch are the Founding Fathers that
contributed many discoveries and uses that we still use today.
4.) All the discoveries are important to the development of microbiology but the ones that stand out
the most are Koch’s postulates, Pasteur’s work on fermentation, the debunking of the spontaneous
generation theory and the immunological studies. After each discovery or observation, a new
technology or way of preventing disease came to play.
1.) Medical microbiology is the study of infectious diseases and controlling potentially dangerous
pathogens. Public health microbiology is much like medical microbiology in that microbiologists try
to control the spread of diseases and indentify them. Immunology deals with the immune system and
how the body protects itself from microbiology. Agricultural microbiology is concerned with
microorganisms that can affect plants and animals. Microbial ecology is the specialty of
relationships between microorganisms and their habitats, both living and nonliving. Microbial
genetics and molecular biology focus of the study of microorganisms to learn about genetic
information and its impact of the development and functions of cells and organisms.
2.) Microorganisms are useful to biologist to study because they replicate so fast, they are easy to
isolate and they can be observed in a laboratory setting or in their natural environment.
3.) Water and sewer sanitation, hospitals, local farms, personal gardens, food production and
distribution.
Page 15
1.) Medical microbiology, public health microbiology, immunology, microbial ecology, and
environmental microbiology are the five most important research areas in microbiology. In order to
have a good quality of life, people are generally free of disease. The prevention (medical
microbiology, public health microbiology and immunology) and study of future and present dieases
(microbial ecology and environmental microbiology) are important to keep people free of disease
and lead a healthy, good quality life.
Chapter 2 (pages 18, 25, 28, 31, and 37)
Page 18
1.) Refraction: bending of light when a light passes from medium to another
Refractive index: measure of how greatly a substance slows the velocity of light
Focal point: specific point where light rays meet after being focused by a convex lens
Focal length: distance between the center of the lens and the focal point
2.) Prisms bend light because glass has a different refractive index than air. When light strikes a
prism, it is bent toward the first normal, or a line perpendicular to the surface of the prism. As it
leaves the glass, it is bent away from the second normal. Lens act like a multiple prisms that bend
light and magnify it so we can see tiny objects.
3.) A lens with a short focal length has a stronger lens and magnifies an object more. A weaker
lens has a longer focal length and magnifies an object less.
Page 25
1.) Ocular (eyepiece): adjustment eyepieces where the image is viewed
Body: contains mirrors and prisms
Nosepiece: houses the objective lens
Objective Lens: three to five lens with different magnifying power and can be rotated to
position objective beneath the body assembly to view specimen
Mechanical Stage: holds specimen with clips, can be moved
Substage Condenser: concentrates light through a cone
Aperture diaphragm control: controls resolution and contrast of image
Base with light source: houses light and acts as a structural base for microscope
Field diaphragm lever: part of the substage condenser controls the angle of the cone of light
emerging from the top of the condenser
Light intensity control: control how much light shows through from under stage
Arm: structural piece of microscope
Coarse focus adjustment knob: first device for focusing; use with 4x objective for sharp focusing
Fine focus adjustment knob: use with all other objectives to focus image slightly
Stage adjustment knobs: move specimen side to side; use it to center specimen
2.) Resolution: the ability to see something clearly. Numerical aperture: ability of the lens to
gather light. Working distance: the distance between the front surface of the lens and the
surface of the cover glass or the specimen when it is in sharp focus. Fluorochrome: special
dye molecules that fluoresce when they absorb light.
3.) A 5x objective with a 15x eyepiece magnifies an image 75x.
4.) Resolution depends on wavelength of light, refractive index and numerical aperture because
they all help to clarify an image so you can see it clearly. Numerical aperture (ablility of the
lens to gather light) is determined by the refractive index of the medium and the angel of the
cone of light entering the objective. The greatest resolution is determined by the largest
numerical aperture and the light of the shortest wavelength. Resolution and magnification are
related because in order to see something small (magnification), you need to see it clearly
(resolution).
5.) The function of immersion oil is to raise the refractive index to achieve higher resolution.
Immersion oil is a colorless liquid that has the same refractive index as glass.
6.) Most light microscopes don’t use 30x ocular lenses because you will not see anymore detail if
the magnification is over than 1,500 to 10,000x. A light microscope with a magnification of
10,000x would produce a blur.
7.) A dark-field microscope utilizes a hollow cone of light to illuminate a bright image on a dark
background. It allows us to view the internal structure of living, unstained cells. Phasecontrast microscopes allow us to view living, unstained cells on a bright background by
converting differences in refractive index and cell density. Differential interference contrast
microscope is similar to the Phase-contrast microscope and uses two beams of light at right
angles. This microscope lets us structures in 3D of living, unstained specimens.
Page 28
1.) Fixation: process in which the internal and external structures of cells and
microorganisms are fixed into position. Dye: a substance used to color materials such as cells,
tissues, and microorganisms. Chromophore: a chemical with double bonds that gives dye its
color by absorbing visible light. Basic dye: dye with positively charged groups that bind to
negatively charged molecules like nucleic acids and surfaces of Procaryotic cells. Acidic dyes:
dyes that have a negative charge which bind to positively charged cell structures. Simple
staining: process in which a single dye is used to color microorganisms. Differential staining: a
staining process that is used to distinguish organisms based on how they stain. Mordant: having
the ability to fix colors, as in dyeing. Negative staining: a wet culture is stained usually with
nigrosin then viewed through a microscope; the specimen appears light on a dark background;
background not the cell is stained. Acid-fast staining: bacteria that have cells walls with a high
lipid content are heated then observed and those which are not easily decolorized by acidalcohol are acid-fast.
2.) Heat fixation is used to observe prokaryotes by heating the cells gently on a slide while
passing through a flame. Chemical fixation uses chemicals mixtures that contain ethanol, acetic
acid, mercuric chloride, formaldehyde or glutaraldehyde. Chemical fixation is used to view
larger and more delicate microorganisms such as protozoa.
3.) Basic dyes are more effective under alkaline conditions because basic dyes are
positively charged salts and the alkaline conditions contain salts as well. The dye will move
from the high concentration of the alkaline conditions into the cell with low concentrations of
positively charged salts.
4.) Gram stain procedure: 1.) Apply crystal violet dye. 2.) Wash with ethanol or acetone.
3.) Apply a different color dye. When the crystal violet dye is applied, it binds with all
bacteria. The ethanol or acetone wash will wash away the color in gram negative bacteria but
leave gram positive bacteria with a violet color. When the different color is applied, the gram
negative bacteria bind to that color.
5.) Capsules require a staining technique where cells are mixed with dye that spread out on
a slide to air dry. After they are dry, the cells appear lighter against a dark background. Capsule
staining is an example of negative staining. Endospore staining is like acid-fast staining and
requires a harsh treatment for the endospore to dye. Flagellum staining requires the use of
mordants and stains such as pararosaniline or basic fuchsin. Flagella have to be stain to be
viewed with a light microscope.
Page 31
1.) The transmission electron microscope has a greater resolution than a light microscope
because electrons have shorter wavelength. Resolution increases with a decrease in the
wavelength of light.
2.) A TEM uses electrons that are focused by a condenser. The electrons are further
focused through magnetic lenses. A TEM must use a high vacuum because electrons collide
with air molecules; having a high vacuum decreases this chance of collision. Thin sections are
used with a TEM because electrons can be absorbed into a specimen or solid matter after being
by deflected by air molecules.
3.) Paraffin sectioning cannot be used for preparing a specimen for TEM because it is not a
thin section. Electrons would absorb and bounce off the paraffin.
4.) Negative staining is used to study structures of viruses, bacterial gas vacuoles and other
such specimens. Shadowing is used to study the morphology of viruses, DNA and procaryotic
flagella. The freeze-etching technique is utilized to see the shape of microorganism organelles.
5.) ATEM forms images from radiation passing through a specimen. The Scanning electron
microscope scans the specimen with electrons. When those electrons hit the surface of the
specimen, secondary electrons are released and trapped by a special detector. From there, the
secondary electrons hit a scintillator that emits light and is then converted to an image. SEMs
are used to examine the surfaces of microorganisms.
Page 37
1.) Confocal microscopes use a laser to scan the to illuminate the specimen and has an
aperture above the objective lens. The aperture elimates stray light. The only light used to view
the image is from the pane of focus. Confocal micropscopes are connected to a computer
which then uses the information gathered to create an clear image . Because of this connection,
confocal microscopes can create 3D images of the specimen. Confocal microspcopes can also
be used to give cross-sections views of the specimen so it can be seen from three perspectives.
Using the three perspectives and 3D imaging, we can see and observe thicker specimens better.
2.) The scanning probe microscope measures the surface of specimens by using a sharp
probe on the specimen’s surface. The scanning tunneling microscope uses a needlelike probe
that is so sharp it can hold only one atom on the tip. It is lowered to the specimen surface until
its electron cloud is in contact with the surface atoms. When small voltage is applied between
this contact, electrons flow through a channel; this is know as tunneling current. The atomic
force microscope uses a laser between its tip and the surface instead of a tunneling current. The
atomic force microscope studies surfaces that do not conduct electricity well and where the
scanning tunneling microscope would not work.
Chapter 3 (pages 42, 48, 50, 53, 65, 70, 73 & 75)
Page 42
1.) Cocci (round), Diplococci (two round), Bacillus (rod), spirilla, and mycelium
(filamentous). Bacterial cells cluster together to from chains, squares or they pair up.
The same shapes usually cluster together.
2.) Bacterial Cell
Page 48
1.) The plasma membrane of procaryotic cell serves as a selectively permeable barrier and
interacts with the world outside of the cell.
2.) The fluid mosaic model for cells consist of lipid bilayers and proteins. The membrane
has 2 layers made up of hydrophilic heads and hydrophobic tails. In between the layers,
proteins are buried with the hydrophilic poking out of the membrane surface. There are
also proteins attached loosely on the membrane surface and buried in the membrane as
well.
3.) Bacterial membranes contain phospholipids and hopanoids. Hopaniods are sterol-like
molecules. Archaeal membranes have hydrocarbons attached to glycerol by ether links
and can from monolayers and/or bilayers. Bacterial and Arachael membranes both have
two hydrophilic surfaces and a hydrophobic core.
4.) Bacteria adjust to environmental conditions, such as heat, by having a composition of
lipids that is not evenly distributed. Bacteria also use fatty acid in their membrane
because of their lower melting points. Archaea adjust their membranes in response to
environmental conditions by having a mixed membrane. Some regions of the
membrane are monolayered and other areas are bilayered.
Page 50
1.) The cytoplasmic matrix is largely made up of water and is a part of the protoplast. The
cytolasmix matrix is also the substance in which the following are suspended:
nucleoids, inclusion bodies and ribosomes.
2.) Cytoskeletal proteins aid in maintaining cell shape. Inclusion bodies are granules of
material located in the cytoplasmic matrix and are used for storage. They can be made
of either organic or inorganic material and are enclosed by a shell are float freely in the
cytoplasm. Ribosomes are made up of protein and Rna and are the site of protein
synthesis. Two types of ribosomes are cytoplasmic ribosomes and plasma membrane
ribosomes.
3.) The most common types of inclusion bodies are: polyphosphate granules, cyanophycin
granulaes, glycogen granules, carboxysome, glycogen and sulfur granules.
4.) A gas vacuole is hollow and impermeable to water but is permeable to air. This
impermeable/permeable relationship allows the gas vacuole to inflate so that the cell
can float and reach light, oxygen and nutrients.
Page 53
1.) Prokaryotes have a nucleiod instead of a membrane-enclosed nucleus. The nucleoid
contains a double-stranded, circular DNA, but some prokaryotes have linear DNA. In
growing cells, the nucleoid has projections that contain DNA and extend into the
cytoplasmic matrix. Inside the projections the DNA is being transcribed to produce
mRNA.
2.) Planctomycetes, Pirellula and Gemmata obscuriglobus are exceptions in terms of their
chromosome or nucleiod structure. The phyla Planctomycetes have a membrane-bound
region containing DNA. Pirellula has a membrane that surrounds the region which
contains a nucleiod and ribosome-like particles. Gemmata obscuriglobus has a nuclear
body with two membranes surrounding it. Having a membrane-bound DNA region
would make replication a slower process for the above genera but would also protect
the DNA from other prokaryotes that can inject plasmids or their own DNA. They
would be able to live in hostile environments or competitive environments.
Page 65
1.) Type І Pathway is present in gram positive and negative bacteria, and Arcahea. It is an
integral protein that transports many things such as solutes, amino acids, toxins and
proteins. Type П Pathway spans all sections of the membrane but only transports things
through the outer membrane. Because of this, it its dependent on the Sec Pathway. Type
П Pathway transports proteins and toxins. Type Ш Pathway is shaped like a syringe
and spans all parts of the membrane. It is used to secrete proteins and virulence factors
in gram negative pathogens. Type IV Pathway secretes DNA and proteins through a
syringe-shaped protein. It spans all parts of the membrane and may be sac-dependent.
Type V Pathway is sec-dependent and used by many auto transporters that can from
their own channel through the outer membrane.
2.) Type І Pathway is more widespread.
3.) Signal peptide: is a short peptide made of amino acid that directs protein
transportation. The signal peptide is not removed until after the protein has translocated
just in cause the signal peptide needs to aid in directing the unfolded protein again.
Page 70
1.) Capsules are a layer of extra material outside of the cell lying on top of the plasma
membrane and serves as extra protection. A slime layer is a layer over the plasma
membrane that is made of uneven, slimy material and aids in movement. Glycocalyxes
are layers like capsules and slime layers that are made up of polysaccharides. S-layers
are structural layers composed of protein or glycoprotein and are located externally to
the cell wall. The S-layer aids in protection and shape maintenance.
2.) Fimbriae are hair-like structures located on the outside of the cell that help attach the
cell to other surfaces or aid in movement. Sex pili are also hair like structures but are
bigger than fimbriae. They are required for conjugation and are determined by
conjugative plasmids.
3.) Bacteria species differ in their flagella distribution patterns. Bacteria can have one
flagellum and if it is located at an end, it is called a polar flagellum. Some bacteria have
one flagellum at each pole while others have clusters of flagella at one of both ends.
Flagella can also be spread evenly over the bacteria’s surface. Flagella consist of a
basal body which is embedded in the cell and a hook that acts as a flexible coupling.
Flagella are synthesized according to multiple genes and can assemble themselves
without the aid of other factors. Procaryotic flagella move as a propeller in a circular
motion to tumble and run forward.
4.) Self-assembly is the synthesis of filaments where structures form through the
association of their component parts without the aid of other factors. It makes sense that
flagella filament is assembled this way so other factors don’t have to channel the
proteins to the outside of the cell to assemble the filament and it decreases the chances
of the proteins not being lost outside of the cell.
Page 73
1.) Chemotaxis: attraction and movement toward or away from chemicals. Run: the path
of a bacterium’s travel in a straight line or slight curve. Tumble: random reorientation
of a bacterium resulting in its facing the other direction.
2.) Bacteria can detect chemicals, such as food or toxins, through receptors. Bacteria will
run towards detected food or stop and tumble away from toxins.
Page 75
1.) Bacterial endospore
2.) Endospores form when nutrients and likable environments don’t exist, which is called
sporogenesis. This process leaves cells dormant until the environment changes and nutrients
are available. When nutrients are available, germination occurs. Germination is when the
endospore releases its contents so that the mother cell, or sporangium, can thrive once more.
The importance of an endospore is to be able for it to survive when we try to sterilize solutions
and objects. Dipicolince acid with calcium ions might be the reason why endospores are
resistant to heat and other lethal agents.
3.) Bacteria that form true endospores are gram-positive and are vegetative bacterial cells.
They are resistant to environmental stresses.
4.) Dehydration of the protoplast is important to heat resistance because it protects the
cortex from heat and radiation damage.
Chapter 5 (pages 102, 103, 105, 110, 113, and 117)
Page 102
1.) Nutrients are substances required for microbial growth and are used in energy release
and biosynthesis. Elements that are required by microorganisms in large amounts are called
macroelements. Nutrients needed in small amounts are called micronutrients are or trace
elements.
2.) The six most important macroelements are carbon, oxygen, hydrogen, nitrogen, sulfur
and phosphorous. These macroelements make up carbohydrates, lipids, proteins and
nucleic acids.
3.) Manganese and cobalt are two trace elements. Trace elements are apart of enzymes and
aid in the catalysis of reactions. Micronutrients also help maintain protein structure.
4.) Heterotroph: an organism that uses reduced, preformed organic molecules as their
carbon source. Autotroph: an organism that uses carbon dioxide as their source of
carbon.
Page 103
1.) Microorganisms are classified according to where they get their energy, carbon source
and what type of electron source they use. For carbon sources, microorganisms are
classified whether they uses carbon dioxide (Autotroph) or organic molecules from
other organisms (Heterotroph). Microorganism are also classified by energy sources in
two groups; Phototrophic organisms use light as an energy source and Chemotropic
organisms use oxidized organic or inorganic molecules. Microorganisms that use
reduced inorganic molecules for an electron source are called Lithotrophs.
Organotrophs get their electron source from organic molecules. Microogranisms can
use any combination of sources.
3.) Riboflavin, coenzyme A, vitamin B12, vitamin C, and vitamin D are growth factors
produced by microorganisms industrially.
4.) Glucose can be made by putting other molecules together. Growth factors such as
amino acids, purines and pyrimidines cannot. That is why glucose is not considered a
growth factor.
Page 110
1.) 1. Chromosome replication and partitioning
2. Cytokinesis
2.) Similar1.) Both replicate 2.) Both produce 2 new cells
Differ 1.) Eukaryotic DNA is linear so it takes longer to replicate. 2.) Prokaryotes
replicate faster due to circular DNA
3.) Paraffin sectioning cannot be used for preparing a specimen for TEM because it is not
a thin section. Electrons would absorb and bounce off the parafin.
4.) A porin is a protein that forms a channel across the outer membrane of the gramnegative bacterial cell wall while ABC transporters span the entire membrane. Porins
are open channels while ABC transporters need a ATP to help proteins or other
materials pass through the gate.
5.) Siderophore are organic moeluces that are able to bind with ferri iron and bring it into
a cell. They are important because they bring ferric iron, which is hard for a cell to
uptake, into the cell.
Page 113
1.) Defined media: A medium in which all components are known. It can be in a broth
form or solidified. They are used to culture microbes such as cyanobacteria and
photosynthetic protists which are photolithotrophic autotrophs.
Complex media: Media that contain some ingredients of unknown chemicals. Complex
media may contain blood, yeast or meat extract. Examples of Complex media are
nutrient broth (contains peptone and beef extract), Tryptic soy broth and MacConkey
agar.
Supportive media: Medium that sustains the growth of many microorganisms. Some
examples of supportive media are tryptic soy broth or tryptic soy agar.
Enriched media: Supportive media that is fortified and encourages the growth of
demanding microbes. Example of enriched media is blood agar.
Selective media: Media that favors the growth of particular microbes. Examples of
selective media are MacConkey agar, endo agar and eosin methylene blue agar.
Differential media: Media that distinguish among different microbes and lead to
identification of microbes based on characteristics. An example of differential media is
blood agar.
2.) Peptones are protein hydrolysates that serve as sources of carbon, energy and nitrogen.
Agar is extracted from red algae and is a solidifying agent. Beef extract and yeast
extract are used as nutrients in nutrient broth, tryptic soy broth and MacConkey agar.
Peptones, agar, beef and yeast extract are used in media because they are nutrients that
the microbes can take in and grow. Agar is used in media as a solidifying agent and can
withstand temperatures between 45 and 90 degrees Celsius. This wide temperature
range comes in handy when certain microbes need to grow in a certain temperature
range.
Page 117
1.) Pure cultures: a population of cells that came from a single cell. Pure cultures are important
because they let us isolate and study one microorganism at a time. To obtain sample for a
Streak plate: Flame the loop, open the tube, flame the neck of tube, insert loop and remove
small sample, flame the neck again, close the tube, inoculate plate in streaks, then flame loop
again. To inoculate a Streak plate: Streak the plate in one corner then flame the loop. Starting
from the first corner, drag the loop across and streak in a second quadrant then flame the loop.
Repeat streaking pattern with dragging the loop in the previous quadrant two more times, only
overlapping each quadrant with one streak, and flaming the loop after each quadrant. To
obtain a sample for a Spread technique: Use the same technique as for the Streak plate. To
inoculate the plate: Spread the loop in a crosshatch pattern over the plate. The Pour-plate
technique use a diluted sample several times then is mixed with warm agar and poured into
Petri dishes.
2.) Colonies grow more rapidly on the colony edge and are thicker at the center. Cell autolysis,
or self-digestion, occurs in older portions of the colony. Nutrition supply and demand,
Chemotaxis and liquid on the surface of the agar affect variations in growth.
3.) An enrichment culture could be used to isolate bacteria capable of degrading hazardous
wastes by mixing blood agar and other nutrients with hazardous material. Then it could be
observed to see if they use the nutrition and digest the hazardous material as well.