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Micro Bio Lab Final

Terms in this set (53)

Lab 5
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If all of your plates had been TNTC or TFTC, what could you do differently next time to improve your chances for success?
If all of the plates were TNTC or TFTC, then changing the dilutions that are plated would solve the problem. For example, if the 10-6 plates were TNTC, then further dilutions, to 10-7, 10-8, and 10-9 might produce better results. If all of the plates were TFTC, then making plates from earlier dilution tubes, such as 10-3 or 10-4 might help.
Why is a plate considered TNTC when there is more than 300?
When more than 300 colonies are present, it is NOT safe to assume that each colony arose from a single cell. With this number of colonies, it becomes likely that in some parts of the plate, TWO cells landed close enough to each other to look like a single colony.
Why is less than 30 considered TFTC?
When fewer than 30 colonies are present, it is safe to assume that each colony arose from a single cell. However, with such a small number of colonies, a small amount of variation would have a large effect on the final number.
What sterilizes the spreader between uses?
Ethanol. The flame is used to remove the residual ethanol, which would otherwise kill the cells
on the plate.
Lab 7
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Can a selective growth medium also be differential?
Selective media favor the growth of some microbes, and inhibit the growth of others. Differential
media produce a visible result when a particular property is present. We discussed and used several
examples of media that are BOTH selective and differential, including mannitol salt agar and eosin
methylene blue. We also used a medium that is differential but not selective - blood agar.
Mannitol Salt Agar is made of mannitol, salt, and phenol red. What does each component do?
The salt is at a high concentration (7.5%) and acts as a selective agent, preventing the growth of most
microbes. Mannitol is a sugar that some bacteria can ferment, and phenol red is a pH indicator that turns a
bright yellow under acidic conditions. Mannitol Salt agar plate selects for Staphylococcus, and
differentiates between S. aureus, which produces acid, from other Staph., which do not.
Would you expect there to be more bacterial growth from the oral swab on blood agar than nutrient agar?
You would expect a larger number of colonies, and a greater variety of colony types. Many of the
bacteria found in the normal human mouth (including many bacteria in the Streptococcus and Neisseria
genuses) grow poorly or not at all on nutrient agar. Sometimes, there is so much growth on both plates
that it is impossible to see a difference. Sometimes the swab used on the blood agar plate simply didn't
pick up enough saliva.
Can skin be sterilized?
Treatments that would kill or remove all viable microorganisms would also destroy the skin. The skin
can never be completely sterilized.
Would you expect a colony that is hemolytic to be pathogenic?
Species and strains of bacteria that are hemolytic are not always pathogens. However, for some
pathogens, the presence of a hemolysin is an important virulence factor.
Lab 9
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List 4 physical methods of sterilization
Dry Heat:
- 300o
F or hotter for three to four hours (oven); works by denaturing proteins and then drying out
microbes.
- 1600oF for a shorter period of time (incineration); works by completely burning up biological
molecules (breaking down covalent bonds).
Wet Heat:
- autoclaving - 121oC, 15 psi; denatures proteins
Filtration:
- physically removes microbes based on their size; works if the filter has pore size small enough
to remove the microbes.
Irradiation:
- Ultraviolet (UV) - can sterilize surfaces if enough UV for enough time; can sterilize solutions if
they aren't turbid, or even air if it isn't too dusty.
- Gamma-Irradiation or X-irradiation - can penetrate through materials; can sterilize packages
food or lab plastics (such as wrapped syringes).
Is unpigmented bacteria more or less protected from UV light compared to pigmented bacteria
Pigment can protect bacteria from the effects of UV, just as it protects human skin. This is one of the
main reasons that microbes produce pigments (especially for microbes that do not perform phagocytosis). So a non-pigmented strain of S. marcescens would be more sensitive to UV than a pigmented strain. Non-pigmented E. coli would probably also be more sensitive.
Why isn't UV considered as an effective sterilization method?
A major limitation of UV is that it does not penetrate well. A plastic lid, a sheet of paper, or even a thin
layer of agar is enough to protect cells from the harmful effects of UV.
What are other kinds of irradiation used in sterilization?
Gamma irradiation and X-rays. Both penetrate well. Neither contaminates the material with radioactivity. The limitation of both of these approaches is that they require a large, bulky, expensive source of the irradiation.
Does turbidity effect the effectives of UV sterilization?
Yes. UV does not penetrate well. Turbidity would block the UV from penetrating through the liquid.
Lab 10
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What is "Bacteriostatic"?
"Bacteriostatic" refers to the ability of an agent to inhibit the growth of bacteria. Bactericidal, in contrast, refers to an agent that kills bacteria.
disinfectant vs antiseptic
A disinfectant is a chemical agent that kills, removes, or inhibits pathogens (disease-causing organisms). An antiseptic is an anti-microbial agent that can be used on tissues of the body. Some disinfectants are highly toxic to living tissues and cannot be used as antiseptics.
What is the zone of inhibition?
The "zone of inhibition" is the region on a heavily-inoculated Petri plate where no bacterial growth is
seen. This zone surrounds a paper disk containing a chemical agent that inhibits bacterial growth or kills
the cells. As the agent diffuses into the agar, it prevents bacteria in the vicinity of the disk from growing.
How do you know if no growth in the zone of inhibition is the result of inhibited growth or death?
Failure of cells to grow within the zone of inhibition could be due EITHER to inhibition or to killing of
the cells. It is not possible to tell the difference simply by observing the presence of a zone of inhibition.
It would be possible to test whether the cells in the zone are alive or dead by sub-culturing - touching a
sterile inoculating loop to the zone and then streaking a fresh, antibiotic-free plate. If colonies are seen,
then the cells in the zone of inhibition on the first plate were not dead, but merely inhibited.
What is "Minimum inhibitory concentration"?
"Minimum inhibitory concentration" refers to the idea that for every drug that inhibits or kills bacteria,
there is a minimum dose required for this effect. On a disk diffusion plate, as the anti-microbial
compound diffuses into the agar, the concentration decreases as distance from the disk increases. The
point at which the concentration becomes so low that it is no longer effective is where growth starts, so
the minimum inhibitory concentration is right at the edge of the zone of inhibition.
Lab 11
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With staining, what structures would be visible in individual yeast or protozoa cells that wouldn't be visible in individual bacteria cells
Yeast cells and protozoa are eukaryotic, and therefore have structures like the nucleus, nucleolus, and mitochondria, among others. Bacteria lack these structures.
What's the difference between budding and binary fission?
Binary fission, the process of cell division used by most bacteria, involves duplication of cellular contents followed by division of the cell (usually) in the middle, to produce two identical daughter cells. Budding, the form of cell division used by yeasts, is an asymmetrical cell division in which the daughter cell forms as an outgrowth from the side of the mother cell. The bud continues to grow until it eventually breaks off and becomes a mature yeast cell itself.
Because fungi are decomposers, how does this relate to how they produce antibiotics?
Saprobes produce antibiotics to inhibit the growth of bacteria, largely to prevent competition for food (since soil bacteria are also generally saprobes).
What is a cyst and a Trophozoite?
Many protozoa undergo two or more stages in their life cycle. Many produce cysts, which are more resistant dormant cells protected by a tough exterior shell. It is often the cyst that is infectious. Trophozoites are the mature, actively growing and dividing form of the organism; the trophozoites of many pathogens survive poorly or not at all outside of the body.
Trichenella transmission and disease
Transmission of Trichenella (which causes trichinosis) occurs when infected tissue (usually muscle) is eaten under-cooked. There normally would NOT be natural transmission of Trichenella person-to-person, although it would be possible to transmit the disease through transplantation.
Plasmodium transmission and disease
Plasmodium causes malaria, a prolific disease that causes 100 million human infection each year.
Transmission does not occur directly from person-to-person, but via mosquitoes, although blood
transfusion could transfer infection directly from one person to another.
Giardia transmission and disease
Giardia infects the small intestine and can cause both acute diarrhea and chronic infections. Giardia is highly contagious and is spread by fecal contamination (for example, of swimming areas) or contact with feces or feces-contaminated objects.
Balantidium coli disease and what structure
cilia and causes gastrointestinal infections.
Giardia lamblia disease and what structure
flagella and gastrointestinal infection,
Trichomonas vaginalis disease and what structure
flagella and vaginal infections
trypanosomes disease and what structure
flagella and African Sleeping Sickness,
Entamoeba histolytica disease and what structure
acute amoebic dysentery and also chronic gastrointestinal infections. and non motile
Plasmodium, disease and what structure
malaria, and non motile
Pinworm lifecycle
Enterobius, the pinworm, initiates infection when eggs are accidentally ingested, typically
when contaminated fingers are placed in a mouth or on food. The worms mature and mate in the large
intestine. Females crawl out of the anus and lay eggs on the skin in the perianal region (see Figure 14.2).
The eggs get into bedding, clothing, and related items like stuffed animals. Fingers get contaminated by
contact with these objects or by scratching the perianal region, which itches when eggs are laid. The
worms live for about two months, but patients often re-infect themselves.
Tapeworm life cycle
A mature tapeworm contains many
segments, in different stages of maturation. The segments at the tail end of the worm are filled with
developed eggs. These terminal segments (called proglottids) break off and are released in feces. The
eggs are released, and are then ingested by an animal. When the eggs hatch, the larva burrow through the
intestinal wall and migrate through the body, entering muscle and other tissues and forming a cyst. When
an animal (including a human) eats raw or undercooked infected tissue, the cyst develops into an adult
worm, attaching to the wall of the small intestine. As the worm matures, proglottids are again released.
Schistosome life cycle
An infected human or other animal
releases eggs in feces; the eggs reach a body of water, hatch, and are ingested by a snail. The worms
develop in the snail, are released into the water, and then infect a human or other animal by burrowing
through the skin. The worms mature, mate, and release eggs into the feces.
Enterobius transmission
Humans get infected by contact with a contaminated object- a finger from an infected person, a fomite, or by ingesting something (such as food) touched by a
contaminated finger.
Trichenella transmission
only acquired by eating undercooked, contaminated meat. It is not transmitted human-to-
human.
Fasciolopsis transmission
uses snails for part of their life cycle. Eggs are released in feces, and the
juvenile worms (called cercaria) develop in snails. They are then released into the water and travel to
water vegetation, particularly watercress. Humans ingest the worms at this stage (called metacercaria).
They burrow through the wall of the large intestine, travel to the liver, and release eggs, which are
released in feces.
Ascaris maturation
After ingestion of Ascaris eggs, the worms hatch out, burrow through the wall of the intestine, travel
through blood or lymph to the respiratory tract. They then crawl up out of the lungs to the throat, and are
then swallowed. In the small intestine, they mature and produce eggs.
Lab 1
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What effect does immersion oil have?
. The oil has the same refractive index as glass, which means that more light will pass through the slide and into the objective. Because you are looking at a very small portion of the slide with the oil immersion lens, not enough light enters the eyepiece to make a clear image, UNLESS oil is used
Lab 2
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advantages and disadvantages of bactincerator and bunsen burner
Because the incinerator completely sterilizes the loop or needle in just 5 - 7 seconds, it is often faster
and more effective than using a Bunsen burner. In addition, because the loop or needle is completely
surrounded by the incinerator, if spattering occurs as the wire heats up, it just hits the inside wall of the
incinerator and burns up. The only disadvantage of the incinerator is that it takes 10 minutes to warm up.
If you don't want to wait that long, then the Bunsen burner can be much faster
Lab 3
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Gram positive bacteria and their diseases
Five gram positive disease causing bacteria are named on the first page of the handout, in the section that
discusses endospores. Two of the most important groups of Gram positive pathogens are found in the
Streptococcus genus, which causes diseases including Strep throat (Streptococcal pharyngitis), rheumatic
fever, scarlet fever, meningitis, pneumonia, and skin and wound infections, and in the Staphylococcus genus
(primarily S. aureus) which causes skin and wound infections, food poisoning, and toxic shock syndrome,
among other diseases.
Gram negative bacteria and their diseases
. There are many important Gram negative pathogens. This semester we've already discussed a few,
including E. coli, which causes urinary tract infections and food poisoning, among other things. Also the
Salmonella (gastrointestinal infection); Neisseria (a diplococcus that includes the species responsible for
gonorrhoea and some cases of bacterial meningitis); Treponema pallidum (a spirochete that is the cause of
syphilis), and Borrelia burgdorferi (a spirochete that is the cause of Lyme Disease).
What is the function of an endospore
The endospore is a dormant structure that functions to protect the cell in times when growth conditions
are poor. The endospore is extremely tough and can survive harsh conditions for very long periods.
Eventually, when conditions are again favorable, the spore germinates into a growing, dividing cell.
Why is malachite green rinsed from the normal cells but from endospores?
Malachite green readily rinses out of cells with water (unlike crystal violet and safranin). In the spore
stain, after the rinsing step, the spores remain green even though the cells are now colorless. This is because
the spore coat traps the stain within the spores. Heat caused the spore coat to open up enough to allow the
stain to enter the spores, but when the cells are rinsed with cool water, the spore coat tightens up and traps
the stain inside.
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