Bio lab midterm

why can microbes be found everywhere

they can metabolize many substrates, they require small amounts of nutrients, and they can tolerate a broad range of environments

why is swabbing the bottom of your shoe considered a positive control

there is 100% probability of microbes on your shoe

why do cotton swabs collect more bacteria when theyre wet

the water allows for more microbes to stick to the swab and better represents the microbes that are found in that location

why do you need to move the otton swab back and forth multiple times whencollecting samples

to ensure that as many microbes as possible will be collected and deposited on the plate

why dont we find viruses when we plate our samples

because viruses need a host to live

how do you decide what temperature to incubate the sample in

in the temperature the sample came from

what is colony morphology

a description of what a single colony looks like growing on a plate

why is colony morphology impotant

it is essential in determining the identity of the microbe

what characteristics should be included when describing colony morphology

size, color, texture, shape, elevation, and margin

what are three distinct characteristics to fungal colonies

fuzzy, large, and multicolored

whare are three characteristics that are distinct to bacterial colonies

smooth, small, and single color

words to decribe shape

circular, irregular, filamentous, or rhizoid

terms to describe elevation

raised, convex, flat, umbonate, crateriform

terms to describe margin

entire, undulate, filiform, curled, and lobate

terms to describe texture

smooth, dry, mucoid, or fuzzy

what type of stain is used for a simple stain

basic stain

how do basic stains work

they are positively charged so they can easily bind to bacteria since bacteria are negatively charged

why would you use a simple stain

to determine cell morphology, arrangement, and size

what are three things heat fixing does for your bacterial smear

makes bacteria stick to the slide, kills them so they are not moving around, and also makes them more visible by coagulating cellular proteins

how is cell morphology different than colony morphology

cell morphology describes a singular cell while colony morphology describes a colony of cells

what are the different shapes of bacteria

coccus, bacillus, and coccobacilli

what are the different arrangements of bacteria

staphylo and strepto

what are some advantages for microbes living in aquatic environments

there is plenty of nutrients and limited competition

why are bacteria and fungi mainly studied in this lab

they are everywhere, easy to grow, and big enough to see growing in a media

why can you look at photosynthetic microbes without stain

because they are colorful from they’re photosynthetic pigments

how are protozoa different than cyanobacteria

they are larger and very motile

how algae bencifical to a pond

they are the base food for the food web

how are algae harmful to a pond

in large number’s they can release a toxin into the water that is dangerous to animals

what type of stain is used for a negative stain

acidic stains

how does a acidic stain work

they have a negative charge and since bacteria also have a negative charge they will repel the stain and only the background will be colored

why would you use a negative stain

to record the true size of bacteria and some bacteria can fall apart when heat fixed ruining the slide

what would happen if you heat fixed a negative stain

heat fixing could cause the bacteria to fall a part and ruin the true size of the bacteria

why do you get to use a lot of bacteria on a negative stain

because the large amount of bacteria will be spread over the entire slide with a another slide

why is serial dilutions needed for standard plate count

if you didn’t the entire plate would be covered with bacteria and you wouldn’t be able to count the individual colonies

do you have to start with a pure culture to perform a standard plate count

no

provide three examples of when someone would want to know how much bacteria was in a sample

bacteria in food, in water, in a hospital

why is it important to keep track of the amounts of bacteria you are moving during serial dilutions

to be able to calculate how many bacteria were in the orginal sample

why is it important to change tips while performing serial dilutions

so extra bacteria is not transferred into the tube

why does it matter if you use a sterile diluent when performing serial dilutions

so they is not bacteria in the water

why is mixing tubes important when performing serial dilutions

so the bacteria are evenly distributed throughout the tube so when pipetted an even distribution of bacteria are sucked into the pipette

what is a gram stain

a complex differential stain through a series of staining and decolorization steps will differentiate bacteria based on their cell wall composition

what information does gram stain tell you

if the bacteria gram positive or gram negative

what cell characteristic does the gram stain differentiate

how much peptidoglycan is in the cell wall

what color is a gram negative cell

pink

what color is a gram positive cell

purple

do gram positive cells have a lot or little peptidoglycan in their cell wall

a lot

do gram negative cells have a lot or a little peptidoglycan in their cell wall

a little

what is the primary stain in gram stain

crystal violet

what is the role of crystal violet

to stain all the bacteria purple

what is the mordant in a gram stain

iodine

what is iodine’s role in gram stain

to form a complex with the crystal violet in the cells that have a lot of peptidoglycan

what is the decolorizing agent in gram stain

gram’s alcohol

what is the role of gram’s alcohol in gram stain

to remove crystal violet from the gram negative cells because they did not form a complex with the iodine and can be easily removed.

what is the counter stain in gram stain

safranin

what is the role of safranin

to stain the gram negative cell pink

what happens if you use too many bacteria in your smear for gram stain

you could have a false positive gram positive stain

why are the timings important for gram stain

so the bacteria o not become over stained or under stains making the results unreliable

why are gram controls used

to tell if your stain was accurate or not

what is the purpose of streaking for isolation

to have an isolated colony

why is streaking for isolation commonly done with environmental samples

to identify the bacteria in the environmental sample

why is it important to have isolated colonies to work worth

so tests can be performed to determine what kind of bacteria is present

what are the two ways to streak for isolation

new school method and trident method

do you think you would get isolated colonies if you forgot to sterilize your loop using streaking for isolation methods

no because bacteria would remain on the loop and the number of bacteria would be hard to diminish enough to get an isolated colony

what are aseptic techniques

method to prevent contamination

examples of aseptic techniques used in lab

not leaving things open, sterilizing the loop, working close to the flame, briefly swiping the lip of the vessel through the flame, and being efficient.

what could happen id you are not aseptic in lab

could end up not having a pure culture

what are the two types of solid media we use in micro lab

agar plates and agar slants

what is the type of liquid media we use in lab

broth culture

what is general media

energy sources such as tryptic soy agar (TSA) and tryptic say broth (TSB)

what is the purpose of autoclaving media before using it

to sterilize the media

what do you do when you inoculate the agar

put bacteria on it

what is a pure culture

a singular type of bacteria

why do we use a zig zag streak

just to spread the bacteria since we are not trying to isoable it

what information should be included when labeling plates

name, date, name of sample, and what type of media it is if it is something other than TSA or TSB

why do you label the bottom of the plates

incase the lid falls off and gets mixed up

why do we incubate plates lid side down

it prevents any liquid on the lid from dripping onto the agar

how does UV light kill bacteria

by breaking double stranded DNA

how do we take advantage of using UV light

to disinfect workspaces, hospitals, and tools

what is the disadvantage of using UV light

UV light can not penetrate any material

does UV light sterilize objects

no only disinfects them because to be able to sterilize an object the object must be isolated from the air and since UV light is incapable of getting through whatever you surround the object with it can not sterilize it

how long does it take to kill microbes with UV light

40 seconds

what is selective media

media that contains ingredients that prevent certain types of bacteria from growing

what is differential media

media that contains ingredeints that show different characteristics of bacteria

how are mannitol plates selective

they have a high NaCl concentration so only gram-positive staphylococci can grow in them

how are mannitol plate differential

if the bacteria can ferment mannitol it will change the color of the plate to a yellow

how can mannitol plates tell us if bacteria is pathogenic

because only pathogens can ferment manitol

starting color of mannitol salt agar

red

color of mannitol salt plate with a non pathogenic gram-positive staphylococci bacteria

maroony red

color of a mannitol plate with bacteria that can ferment mannitol

yellow

how are macconkey selective

bile salts and dyes inhibit the growth of gram-positive bacteria

how are macconkey differential

can differentiate between lactose fermenters and non fermenters based on color change

starting color of macconkey agar plates

yellow

what color are macconkey agar plates with bacteria that can ferment lactose

pink

how are eosin methylene blue agar plates selective

dyes in the media prevent gram positive bacteria from growing

how are eosin methylene blue agar plates differential

if bacteria can ferment lactose is will change the pH of the plate and cause a color change

how are eosin methylene blue agar plates semi-quantitative

depending on the amount of lactose fermented different colors of colonies will grow on the plate

what is the starting color of eosin methylene blue agar plates

a dark red/purple

what color is an eosin methylene blue agar plate with bacteria that ferment low levels of lactose

light pink/purple colonies

what color is an eosin methylene blue agar plate with bacteria that ferment high levels of lactose

black or metallic green on the bacterial growth

what color is an eosin methylene blue agar plate with bacteria that ferment medium levels of lactose

darker pink/purple colonies