Microbiology Lab Exam 2 – Flashcards
Unlock all answers in this set
Unlock answersquestion
an ideal machine would have efficiency of ___
answer
100%
question
were any plates completely lacking in colonies
answer
Variable answers
question
why do you suppose this habitat contains such a high microbial count?
answer
possible answers include, temperature, moisture, amount of human traffic.
question
Types of organisms we find on skin?
answer
(gram+ cocci, gram- cocci), soil (gram+ bacilli endosporeformers, gram+ filamentous, molds), in water (gram- bacilli), in dust (gram+ cocci, gram+ bacilli endosporeformers, mold spores, variable)
question
do you think that habitat sampled was really sterile?
answer
no/yes
question
if you answer to be is no, then how can you count for the lack of growth on the plate?
answer
Organisms sampled were not able to grow on the kind of nutrient agar used, or organisms sampled require longer time to grow.
question
if your answer to b is yes defend it?
answer
Students may feel an area sampled is sterile because it was recently cleaned.
question
in what ways do the macroscopic features of bacterial colonies differ from those molds?
answer
Bacterial colonies are generally smooth and small as compared to fungal colonies, which are large and “fuzzy.”
question
why is the level of contamination measured as number of colonies rather than size of colonies?
answer
Since each colony is produced from a single cell, the number of colonies indicates the number of cells originally present or level of contamination. Colony size reflects growth rate. See Ex 38
question
should one be concerned to find bacteria on the skin? how about molds?
answer
Bacteria, such as the staphylococci and the diphtheroids, are part of the normal skin flora. Molds, however, are likely transient contaminants picked up from the environment.
question
how can microbial levels be controlled on the skin? on surfaces in the environment? in the air?
answer
Microbial levels on skin are best controlled by hand washing, on surfaces in the environment with use of disinfectants like bleach, and in the air by HEPA filtration systems.
question
compare the following features of bacteria to those eukaryotic microorganisms? size
answer
Bacteria are smaller, about 0.510 µm in diameter.
question
compare the following features of bacteria to those eukaryotic microorganisms? organization of genetic material?
answer
Bacterial DNA is not enclosed in a nucleus but rather is organized in the cytoplasm.
question
compare the following features of bacteria to those eukaryotic microorganisms? ribosomes?
answer
Bacteria have 70S ribosomes.
question
compare the following features of bacteria to those eukaryotic microorganisms? cell wall?
answer
Bacteria have a cell wall composed of peptidoglycan.
question
compare the following features of bacteria to those eukaryotic microorganisms? respiration and photosynthesis?
answer
Bacteria lack mitochondria and chloroplasts but can carry out respiration and photosynthesis.
question
compare the following features of bacteria to those eukaryotic microorganisms? motility?
answer
Bacteria may have flagella that are simpler in structure but may be more numerous.
question
WHAT KIND OF CHARACTERISTICS CAN WE DETERMINE ABOUT BACTERIA FROM OBSERVING BROTH CULTURES?
answer
Nature of growth on the surface (ring, pellicle, flocculent, membranous), subsurface (turbid, granular, flocculent, flaky), and bottom of tube (sediment). Also, amount of growth.
question
WHAT KIND OF CHARACTERISTICS CAN WE DETERMINE ABOUT BACTERIA FROM OBSERVING SLANT CULTURES? WHY ARE THESE CHARACTERISTICS DIFFERENT THAN BROTH CULTURES? part 1
answer
Amount of growth, color (pigment), opacity (opaque, transparent, translucent), form or shape (filiform, echinulate, beaded, effuse, arborescent, rhizoid).
question
WHAT KIND OF CHARACTERISTICS CAN WE DETERMINE ABOUT BACTERIA FROM OBSERVING SLANT CULTURES? WHY ARE THESE CHARACTERISTICS DIFFERENT THAN BROTH CULTURES? part 2
answer
Bacteria growing on a solid surface takes characteristic shapes that are unique to their species that cannot be observed in broth cultures.
question
WHAT CHARACTERISTICS CAN WE DETERMINE ABOUT BACTERIA FROM OBSERVING ISOLATED COLONIES ON AGAR PLATES? WHAT KIND OF CULTURES ARE BEST TO OBSERVE AND WHY? 1
answer
We can determine size, color, opacity, form (shapes and configurations include round – scalloped/raised/radiating margin, wrinkled, concentric, irregular and spreading, filamentous, L-form, filiform, rhizoid, complex),
question
WHAT CHARACTERISTICS CAN WE DETERMINE ABOUT BACTERIA FROM OBSERVING ISOLATED COLONIES ON AGAR PLATES? WHAT KIND OF CULTURES ARE BEST TO OBSERVE AND WHY? 2
answer
elevation (flat, raised, convex, drop-like, umbonate, hilly, ingrowing, craterform), and margin (smooth or entire, wavy or undulated, lobate, irregular, ciliate, branching, wooly, thread-like, hair-like).
question
WHAT CHARACTERISTICS CAN WE DETERMINE ABOUT BACTERIA FROM OBSERVING ISOLATED COLONIES ON AGAR PLATES? WHAT KIND OF CULTURES ARE BEST TO OBSERVE AND WHY? 3
answer
Pure cultures with isolated colonies are best to observe, because if more than one species of bacteria contribute to a colony, it will have a mixture of growth characteristics, and therefore cannot be used to help identify an unknown.
question
which bacterial species exhibited true motility on the slides?
answer
Proteus is motile.
question
Did the semisolid medium inoculations concur with the slides results?
answer
Variable; however, the semisolid medium inoculations should concur with slide results. Pink spreading due to TTC oxidation in motile organism (Proteus).
question
describe the differences between the two stabs in the soft agar plate and based on these results which species appears to be motile
answer
Growth extends farther from the stab location for the motile bacterium. Proteus is motile.
question
describe the structure of flagellum.
answer
A bacterial flagellum is a fibrous appendage composed of protein subunits and anchored in the membrane.
question
how do flagella general cell motility?
answer
Flagella rotate counterclockwise to propel the cell forward and clockwise to tumble and change direction.
question
if you compared tow motile bacterial species and determined one was considerably more motile than the other which arrangement of flagella would you expect to be associated with the highly motile species and how would you confirm this?
answer
Peritrichous flagella, which are numerous arrangements across the entire cell surface, are characteristic of highly motile bacteria, such as Proteus. Confirm the flagellar arrangement with a flagella stain
question
differentiate between the following types of movement observed in a wet mount or hanging drop slide? directional motility
answer
Rapid swimming and directional change indicate true motility.
question
differentiate between the following types of movement observed in a wet mount or hanging drop slide? brownian movement
answer
Jiggling motions without movement in a particular direction indicate Brownian movement.
question
differentiate between the following types of movement observed in a wet mount or hanging drop slide? water current movement
answer
Sweeping motion indicates water currents.
question
between wet mount and hanging drop slides preparations which is more resistant to evaporation?
answer
Hanging drop slides are more resistant to evaporation,
question
between wet mount and hanging drop slides preparations which woks best with phase contrast microscopy?
answer
although wet mount slides work better with phase contrast microscopy.
question
what concentration of agar is used in a semisolid medium for motility determination? how does this compare to a typical solid medium?
answer
Less agar is used to make semisolid media, which when stabbed, allow motile bacteria to swim but hold nonmotile in place. Typical solid medium contains 1.5% agar, which when stabbed, would not allow movement of motile bacteria.
question
why are semisolid media sometimes preferred over slide techniques for evaluation bacterial motility? 1
answer
Exposure of individuals to pathogens is more likely when making wet slides as opposed to stabbing a semisolid medium where the bacteria are contained.
question
WHAT IS THE FUNCTION OF TTC IN THE MOTILITY MEDIA?
answer
TTC is useful in easily determining motility.
question
why are semisolid media sometimes preferred over slide techniques for evaluation bacterial motility? 2
answer
There are also fewer false positives when using semisolid media because there is no Brownian movement or water current.
question
complex media
answer
The exact composition of defined media is known whereas it is not known for complex media. Complex media are typically made for rich extracts of meat or plants.
question
defined media
answer
are made by individually measuring out all components.
question
name 6 basic nutritional requirements supplied in all culture media
answer
Basic nutritional requirements in all culture media include a carbon source, an energy source, nitrogen, minerals, vitamins, growth factors, and water.
question
what growth factor is often supplied for cultivation of fastidious bacterial pathogens?
answer
blood
question
autoclaving destroys living cells as well as what other bacterial stage that could cause contamination?
answer
endospours
question
an autoclave is typically used for
answer
sterilization of media?
question
define sterilization
answer
Sterilization is the complete removal or destruction of all microbes including bacterial endospores.
question
under what conditions are media typically sterilized in an autoclave
answer
Media are sterilized at 121?C with 15 psi of steam for at least 15 minutes.
question
what type of media components cannot be sterilized in an autoclave
answer
Heat-sensitive media additives (e.g., antibiotics or milk or enzymes) cannot be sterilized by autoclaving.
question
what is an alternative to an autoclaving for sterilization heat sensitive materials?
answer
Filter sterilization can be used for liquid components that cannot be autoclaved.
question
what compounds or chemicals might be added to a medium to make it selective
answer
A selective medium allows one type of microbe to grow while another is inhibited. It might contain a high/low pH, or a higher salt concentration, or another growth limiting ingredient.
question
agar is solidifying agent used in
answer
media prepration
question
agar is solidifying agent used in media preparation. agar is solidifying agent used in media preparation. what is it's origin
answer
Agar is a complex polysaccharide isolated from seaweed (red algae).
question
agar is solidifying agent used in media preparation. how and why does the agar concentration in semisolid media differ from conventional solid media?
answer
A semisolid medium has an agar concentration of 0.4%, which is in contrast to conventional solid media that has a concentration of 1.5%. Semisolid media can be used for motility studies because they allow movement.
question
agar is solidifying agent used in media preparation. what makes it ideal for cultivation of microbes?
answer
Agar melts at 100?C but does not solidify until it reaches 45?C, which will not kill microbial cells so inoculation of molten media (e.g., pour plates) is possible. Agar is also relatively inert and is not degraded by most microbes.
