lab report questions

true or false: immersion oil is required for the 40x objective lens

false

true or false: brightfield microscopy can be used to view viruses

false

true or false: immersion oil improves image resolution by limiting light refraction

true

which of the following could you use to view a live, unstained sample? select all that apply 🇦

dark-field microscopy

brightfield microscopy

fluorescent microscopy

phase contrast microscopy

dark-field microscopy

phase contrast microscopy

calculate the total magnification for 4x lens, based on an ocular lens of 15x

60x

4x (15x)= 60x

calculate the total magnification for 10x lens, based on an ocular lens of 15x

150x

10x (15x)= 150x

calculate the total magnification for 45x lens, based on an ocular lens of 15x

675x

45x (15x)= 675x

what is the relationship between magnification and working distance?

as magnification increases, working distance decreases

what would happen to your image if you used water instead of oil with the oil immersion lens?

light will be lost due to refraction

how can you determine if the bacteria growing on the broth are the same as that in the agar plate?

you can compare pigment and continue to do more tests

true or false: broth cultures allow for colony formation

false

true or false: broth cultures can be used to observe flocculence

true

true or false: colony morphology may be affected by incubation temperature

true

the presence of a fuzzy, dark centered colony on an agar surface, suggests the growth of

fungal specimen

candida albicans is a fungus that naturally lives in and on the body, and it is only known to cause disease when the host’s normal microbiota is disrupted. what term/phrase best describes this microbe?

opportunistic pathogen

media is sterilized before use; an autoclave is used for this process. what type of heat does an autoclave use to sterilize?

steam

which of the following is (are) required for proper aseptic transfer of a specimen? select all that apply:

sterile media

sterile inoculating instrument

disinfected work bench

limited exposure of the sample to the environment

sterile media, sterile inoculating instrument, disinfected work bench, limited exposure of the sample to the environment

which of the following is FALSE regarding an aseptic transfer from a broth to an agar plate?

broth culture must be mixed before transfer

the loop must be cooled after sterilization

loop must be sterilized until ‘red-hot’ color

test tube cap must be placed down on the bench

test tube cap must be placed down on bench

each nutritional component and quantity are precisely known

defined media

it contains at least two different species

mixed culture

can be performed using a loop or needle

inoculation

sterile nutrient broth is an example

complex media

usually contains an extract or a digest

complex media

suppose you performed an aseptic transfer from a stapylococcis epidermidis stock culture to a nutrient broth (NB), however after proper incubation you do not see any growth. Assuming the media provides necessary nutrients for growth of staphylococcus epidermidis, what error could you have made during the aseptic technique procedure?

did not mix the broth culture and did not allow loop to cool

how do cheek cells compare to bacterial cells

they are much larger

true or false: negative staining requires two or more dyes

false

true or false: negative staining requires a fixed smear

false

true or false: staining more accurately reveals cell morphology than simple staining

false

which of the following can you identify with a negative stain? select all that apply:

cell arrangement

cell shape

cell size

cell wall characteristics

cell arrangement

cell shape

cell size

all of the following are true of negative stains EXCEPT:

it is acidic

it stains the background

it has a positive charge

it has a chromogen

it has a positive charge

what is an advantage of the negative stain over the simple stain

no heat fixation, which can distort cell features

true or false: simple staining requires two or more dyes

false

true or false: simple staining requires a fixed smear

true

true or false: simple staining is performed on a live sample

false

what is the purpose of heat-fixing

adheres cells to slide

kills most of the cells

name two different dyes, besides methylene blue, which can be used for simple staining

crystal violet

safranin

select all the characteristics a simple stain can reveal. select all that apply

cell wall composition

cell shape

cell size

cell arrangement

cell shape

cell size

cell arrangement

select the features of a basic dye. select all that apply

has a chromophore

has a positive charge

it is acidic

stains the background

has a chromophore

has a positive charge

what effect may heat fixation have on the characteristics of a microbe

change the shape of the cell

after preparing a smear of escherichia coli and performing a simple stain you observe your sample. under oil immersion you find there are barely any stained cells on the slide. assuming you used the proper reagents, provide two reasons for this poor staining outcome.

cells were not fixed to slide

did not cool loop→ killed/zapped cells

true or false: the gram stain is a differential stain

true

true or false: the gram stain is best performed in cultures more than 48-hours old

false

what color would gram-positive bacteria be if you forgot to add the counterstain safranin

purple

what color would gram negative bacteria be if you forgot to add counterstain safranin

colorless

what are 4 differences between gram positive and gram negative bacteria

positive: thick cell wall, no outer membrane, no LPS, exotoxins

negative: thin cell wall, outer membrane, LPS endotoxin, no exotoxins

which of the following is true regarding the gram stain?

it is a type of simple stain

it uses alcohol as a mordant

it requires an acidic dye

gram positive bacteria stain purple

it is a type of simple stain

gram positive bacteria stain purple

why is the gram stain clinically useful

to know which treatment/antibiotics to use

assume you perfom a gram stain on a pure culture. after the procedure you observe both gram positive and gram negative cells. what could indicate about the culture or procedure

contamination

true or false: the knyoun method requires heat

false

true or false: acid fast bacteria are considered gram positive

true… but they dont stain well in gram staining

which of the following are differential stains? select all that apply

gram stain

simple stain

negative stain

acid fast stain

gram stain

acid fast stain

what color would nonacid fast bacteria be if you skip the counterstain step

clear

why is the acid fast stain clinically useful

to know which treatments/antibiotics to use

name two diseases caused by acid fast bacilli (AFB) and their respective causative agents

disease: tuberculosis, leprosy

causative agent: mycobacterium tuberculosis, mycobacterium leprae

name one acid fast parasite and the disease they cause

cryptosporidium, causes cryptosporidosis (diarrheal disease)

based on colony characteristics, how can you differentiate between serratia marcescens and staphylococcus epidermidis

S.M.= red pigment, irregular

S.E.= white, raised/convex,circular

regarding the spread plate, what would be the primary consequence of failing to evenly spread the sample

no colony isolation

true or false: the quadrant streak plate is basically a dilution of the sample on a plate

true

true or false: A CFU is always a single cell

false

true or false: a pure culture is derived from a single species

true

how can colony characterisitics (shape, size, pigment) help you identify if you have a pure culture or not

if all colonies on a plate have the same characteristics = pure culture

assume you perform a quadrant streak plate and colony isolation is observed in the first quadrant, but no growth occurs in the other plate quadrants. what most likely led to this scenario

did not transfer correctly from quadrant 1 to quadrant 2, so did not pick up cells