MICROBIOLOGY EXPERIMENTS AND LAB TECHNIQUES QUIZZES

When recording information on an agar plate, the best place to record that information is on

on the back of the dish (underside) near the edge.

Which explanation for why diamond jewelry is a "microbial hotspot" is most accurate?

Microbes anchor in the small crevices of jewelry and are not dislodged during handwashing.

If you move the microscope slide to the right on the stage, does the image (when viewed through the ocular lenses) also appear to move to the right?

No

Which of the following is the best example of a "double blind study"?

Both the participating patients and the conductors of the experiment do not know which patients belong to the experimental group and which patients belong to the control group.

The results of the study are analyzed by a third party, who is not able to distinguish which patients where in the experimental group, and which patients were in the control group.

The chloroplasts in protozoa (such as Euglena) are best observed with

Brightfield microscopy is best at observing organelles with a natural pigment.

Which eukaryotic organism was the largest?

Ameobas

Bacteria

Euglena

Paramecium

Response Feedback:

The Amoebas, which can be seen with the naked eye, were the largest.

The 37C incubator promotes the growth of which type of organism?

Bacteria that normally flourish on a human body.

When analyzing results for the Handwashing Lab, what is the dependent variable, or measurement?

Comparing the number or diversity of colonies.

When using the scanning objective (4X) , how long would the entire ocular micrometer ruler be in inches?

0.1 inch

What is the BEST definition of contamination?

When an unwanted microbe enters a microbial media and grows there.

Compound microscopes are limited to 1000X magnification because

the resolution becomes too poor after 1000X.

What is an appropriate size for an amoeba cell?

300 um

When using the scanning objective (4X), how long would the entire ocular micrometer ruler be in millimeters?

2.5 mm

One would use a Trasmission Electron Microscope when attempting to view

the nucleic acids inside a virus.

The Handwashing Experiment was an example of a double blind study.

False

The aperture of a good "high dry" lens (40x objective lens) is 0.65. If the average wavelength of light is 500 nm, what is the resolving power of this lens (in other words, how close together can two objects be that the lens will still distinguish as two separate points)?

Correct 380 nm = 0.38 υm

In a microbiology preparation room, you are responsible for making microbiology media. The directions say to add 40 grams of dried powder per 1 L of water.

Your boss tells you to make 500 mL of media. How much powder should you add?

Hint: First think about this problem: 500 mL = ______ L

20 g

Match the disease with the morphological shape (from the Discussion of Exercise 9)

Question Correct Match Selected Match

Syphillis

Correct A. Spirochete

Correct A. Spirochete

Gonorrhea

Correct D. Diplococcus

Correct D. Diplococcus

Vaginal Candidiasis

Correct C. Oval/Ovoid

Correct C. Oval/Ovoid

Cholera

Correct B. Vibrio

Correct B. Vibrio

What species forms colonies that are tan/greyish in color, irregular and wrinkled in shape, and dry in texture?

Mycobacterium smegmatis

In the genetic engineering lab, what happened during the 50 second incubation at 42C (i.e. the "heat shock"?)

Pores developed in the cell envelope which allowed plasmid DNA to enter the bacterial cell.

In the conjugation experiment, the original F- strain was resistant to streptomycin.

True

From Page 66 in Lab Exercise #7 - match the following colony sizes with the appropriate species.

Question Correct Match Selected Match

Enterococcus faecalis

Correct C. 1 mm or less

Correct C. 1 mm or less

Serratia marcescens

Correct B. 3 mm

Correct B. 3 mm

Mycobacterium smegmatis

Correct A. 5 mm

Correct A. 5 mm

The texture of Serratia marcescens can best be described as

creamy

In Lab #7, Enterococcus faecalis colonies were colored

white

In the genetic engineering lab, which plate was most likely to exhibit "lawn growth"?

Either the T or C cultures plated on LB only.

How would you describe the texture and color of Micrococcus luteus (Results, Exercise 6)?

creamy (possibly dry) and yellow

(Lab #7) Colonies embedded into the agar of the pour plates were SMALLER than those on the surface of the pour plates. Why?

Colonies growing on the surface had more room to grow and were not limited for space by the solid agar.

What type of experiment is likely to require the use of synthetic media?

A patient with a throat infection is swabbed to identify the causative agent. The swab is streaked and stained (simple) on a slide for viewing with a microscope. After looking at the slide for a few minutes, the M.D. concludes that patient has oral thrush, not a bacterial infection.

In a simple stain, yeast cells can be differentiated by size and shape. They have a characteristic oval shape and are usually much larger than bacterial cells. Indeed, yeast cells can be seen at 400X quite easily (while bacterial cells usually require 1000X)

What is the Gram result of Esherichia coli?

E. coli is Gram -, it stains red/pink.

Which explanation best explains why a 3 month old Staphylococcus culture can appear red after a Gram stain.

The culture is mostly dead cells, which means the peptidoglycan layers have degraded. Thus, the initial dye (crystal violet) does not stay attached to the decayed cell wall.

The gram stain of old Bacillus megaterium for most students produced a mix of purple and magenta colors. Why?

The peptidoglycan began to deteriorate in some older cells and thus the older cells retained less crystal violet and more safranin red compared to fresh cells.

The only acid-fast bacterium (of clinical significance) is Mycobacterium. And, unless gross student error was made, the smears should have been pure. Moreover, Bacillus is a G+ organism, so the crystal violet dye should have been retained on a vegetative cell.

However, the safranin red dye that was often seen was in older cells. The spore coat and often the cell wall of the dying cell (with less peptidoglycan) often stained red once the crystal violet had been removed.

Lysozyme is more effective in killing Gram + bacteria than Gram - bacteria.

True

A Gram + cell will have more sensitivity to Penicillin than a Gram - cell.

True

What would a gram stain of a patient infected with gonorrhea reveal?

The diplococci would be red, showing a Gram - stain.

What structural feature of the Mycobacterium cell causes it to be acid fast?

The outer membrane made of waxy molecules which repels the decolorizing acid alcohol.

What specimen from a tuberculosis patient would the acid fast stain be performed on?

Sputum

Spores are involved in sexual reproduction for bacteria.

False. spore is a type of "hibernation strategy" for a bacterium. The vegetative cell that germinates from a spore is genetically identical to the parent cell. Therefore, there is no sexual reproduction.

Terminal

These endospores were formed at the end of the vegetative cell, making them terminal spores.

What is the primary role of capsules on pathogenicity?

The capsule prevents phagocytosis by our immune cells.

Based on our Experimental Results for Lab #8, which of these species had the shortest (fastest) AVERAGE generation time?

Escherichia coli

When we say that Staphylococcus has a "generation time" of 60 minutes, what does that mean?

One Staphylococcus cell is capable of dividing via binary fission once every 60 minutes.

In dental caries, the role that Streptococcus mutans plays is

S. mutans ferments sucrose into lactic acid, which dissolves the calcium enamel of the teeth.

In the capsule stain, what does carbol fuchsin stain?

Carbol fuchin is the second dye of the capsule stain. As the introduction to this lab states, the second stain is applied to color the cytoplasm of the bacteria. Hence, carbol fuschin stains the vegetative cells.

The CAPSULE STAIN is a type of ____________ stain, because the capsule itself is not easily stained and therefore must be outlined by a background stain.

negative

what is the difference between normal Flora and transient Flora?

normal flora-live naturally in our body transient flora-microbes are temporary and can be removed by hand washing.

what information should include in labeling your lab work?

name, date and name of specimen

what is nosocomial infection ?

get it when you are hospitilized, handwashing helps

define simple microscope

uses single magnifying lens to produce an enlarged image

compound microscope

light microscope that uses two or more lenses to achieve high magnification-see detailed magnification

define parfocal lens

stays in focus as you change its focal length (zoom in or out)

what is refraction lens ?

curved lens, light passes through it, gathering light from the specimen and focusing it to create a magnified, clear image

which objective lens should you use first for viewing a slide and why?

scanning 4x=40x, it provides the widest field of view and lowest magnification

difference between a stage micrometer and ocular micrometer

stage micro. -slide that preasely etched to know the distance apart.

ocular-is a ruler inside the microscope eyepiece

why do we multiply the stage divisions by 10mcm?

Stage micrometer lines are 10 µm apart, so we multiply by 10 µm anytime we use those lines to measure something under the microscope.

using the scanning objective how long would the entire ocular micrometer ruler be in mm?

2.5 mm long.

using the scanning objective how long would the entire ocular micrometer ruler be in inches?

0.098 inches (about 0.1 inch)

what is larger one quart or one liter?

liter

what is larger one yard or one meter?

meter

what is larger one pound or one kilogram?

kilogram

postive TB test in inches

0.2–0.6 inches across

primary syphilis chancre size in metric units

5-20 mm in diameter

what is brightfield microscope?

general background or field of view is bright while dense specimens appear as darker objects, good for stained cells

darkfield microscope

creates the effect of a negative image, the field of view is dark while cells and other objects are lit up, good for motile cells

what is phase contrast in microscope?

increases the contrast between cells or portions of cells that vary only slightly in density. shows detail of no stained cells

fluorescent microscope

uses a light source with ultraviolet rays in it and special filters to allow you to see fluorescence at the microscopic level. used in medicine and research.

electron microscope

uses a beam of electrons rather then a beam of light. used to see viruses, magnification up to 200,000x

transmission electron microscope

transmits beam of electron thorugh an extremely thin section of specimen. used to study structure of organelle

scanning electron microscope

reflects beam of electrons off the exterior of the specimen,three dimensional view of specimen.

Which is more important in quality of microscope lens is it its magnification or resolving power?

Resolving power is more important than magnification.

Why:

• Magnification only makes the image bigger.

• Resolving power determines how clear and detailed the image is (ability to distinguish two close points).

define pseudopodia

amoeba are constantly changing their shape and move by extensions of their cytoplasm

vibrio cholerae is a vibrantly motile bacterium and is the etiology agent cholerae. what type of microscope would be most useful in observing the motility of the microbe?

darkfield microscopy

waht type of microscope would be most helpful in studying the 3D line structure of the surface of microvili from the intestine?

scanning electron microscope

who invented pour plates

robert Koch developed the loeffer and gaffly developed the streak plate

koch postulates

(1) The microbe must be in all diseased individuals but not healthy ones; (2) it must be isolated and grown in pure culture; (3) the pure culture must cause the same disease when introduced to a healthy host; and (4) the microbe must be re-isolated from the new host and match the original

advantages of using agar

allows the use of incubators without melting

purpose of streak plate

to separate the individual microbes form one another

purpose of pour plates

to be able to count the colonies of the bacteria and to have an evenly distributed number of cells throughout the whole sample.

in the dilute pour plates micrococcus what difference sis you notice between colonies growing within the agar and those growing on the surface?

-the colonies growing within the agar were more solid colonies and the colonies growing on the surface of the agar were more "spread out" and had a fuzzy appearance

why are all petri plates incubated upside down ?

to avoid condensation

colony count

>30 or less to few too count, 300> or more too many to count (TMTC)