Lab Midterm

Question 1

What is total magnification

Answer 1

Ocular times objective lens

Question 2

What is field of view

Answer 2

The part of the sample that you are able to see
As magnification or power increases the field of vision decreases

Question 3

What is depth of field

Answer 3

The depth level
Like the strings in top of each other and being able to focus above or below them

Question 4

What is the working distance

Answer 4

Distance between the objective lens and the specimen
Decreases when the magnification or power decreases

Question 5

What is oil immersion and why do we use it

Answer 5

Light doesn’t bend with oil so it gives a better image

Question 6

What is a defined vs complex mixture, compare them

Answer 6

Defined is knowing the exact measurements of each ingredient
Complex is the big mixture that does not have exact numbers

Question 7

What are two reasons to heat fix

Answer 7

Kill bacteria
Adhere them to the slide

Question 8

What is the difference between negative and simple staining

Answer 8

In a negative stain you stain the background and don’t heat fix because that would cause problems with the cell structure
Simple staining you will heat fix and stain the bacteria

Question 9

What three stains did we do in lab 3

Answer 9

Gram stain, endospores, capsule

Question 10

What is the difference between simple and differential in staining

Answer 10

Simple looks at morphology and arrangement
Differential is able to differentiate between types of cells and cell structures such as gram - or + and can see if capsules or spores are present

Question 11

Why don’t you skip any steps in gram staining and what is the difference in cell wall shape and arrangement in gram stain

Answer 11

Decolonizing step is most important because 15 seconds is just long enough to pull the CV out of the gram negative peptidoglycan layer but keep the color in the thick layer of gram positive. If time is too short the CV may stay in the layer of gram - and cause issues when trying to differentiate. If too long the color could be pulled out of both layers which can cause incorrect results as well

Question 12

Come back to endospore and capsule of lab 3

Answer 12

I don’t know what the fuck us going on

Question 13

How do you calculate prevalence

Answer 13

Number of cases/ number of persons

Question 14

What is the meaning of the correlation statistic

Answer 14

The closer the number is to one the more correlation is between the two variables
If the number is closer to zero the variables are not correlated very closely
If the number is negative with high correlation this means as one goes in positive direction the other goes in negative direction but at the same time
Positive number means they both either go up or down at the same time

Question 15

What are the standard vaccines in the U.S (these are what we should know and not pick because she asked to choose which are not core)

Answer 15

Tdap which is tetanus, diphtheria, and pertussis
Rhotovirus
Measles, mumps, rubella
Pneumococcal
Haemophilus influenza
Chicken pox and hep A and B
Polio, varicella, and meningococcal

Question 16

What is macconkey selective and differential for

Answer 16

Selective for gram -
Differential you can tell which bacteria can break down lactose and which cannot

Question 17

What is sulfide in a SIM test

Answer 17

Black is positive meaning H2S is present and clear is negative

Question 18

What is motility in a SIM test

Answer 18

If there is a line it’s motility negative because it shows the bacteria didn’t move
If the bacteria is spread out in the tube it’s motility positive

Question 19

What is the indicator rxn in a SIM

Answer 19

Iron is in the medium which reacts with H2S gas to form iron sulfide

Question 20

What is the putrefaction rxn

Answer 20

When cysteine is converted into pyruvate using cysteine desulfarase and H2S is a by product
This is only one of the ways H2S is made

Question 21

Besides putrefaction what is another way H2S is made

Answer 21

Anaerobic respiration which is when thiosulfate is reduced or picks of electrons and becomes a gas

Question 22

True or false: SIM cannot tell us which of the two rxns made the H2S present in the test it just tells us its present

Answer 22

True

Question 23

What are the results of a blood agar hemolysis

Answer 23

Alpha means partial breakdown of red blood cells using enzymes
Beta is full breakdown
Gamma is no breakdown

Question 24

How does a catalase test work (keep it simple)

Answer 24

Breaks down hydrogen peroxide to water and oxygen and the oxygen is why we see bubbles
Positive test is bubbles and negative is no bubbles

Question 25

What is aerobic catalase

Answer 25

When the bacteria need oxygen so they will have both SOD and catalase, bubbles will be present and they will survive at the to of the tube

Question 26

What is facultative in a catalase test

Answer 26

Prefer to have more oxygen for energy but can live without it so you have positive SOD and catalase You will find them at the top and also dispersed throughout the tube

Question 27

What are anerobes in a catalase test

Answer 27

Don’t use oxygen but don’t hate it they only kill the worst of oxygen Have SOD but not catalase and they are found throughout the tube

Question 28

What are obligate anaerobes in a catalase test

Answer 28

Don’t like oxygen at all so they are both SOD and catalase negative They love far away from oxygen as possible so they are found at bottom of tube

Question 29

What are microaerophiles in a catalase test

Answer 29

Only live in 2-10 percent oxygen Have SOD and only some have catalase Live almost at the top of the tube

Question 30

What are the important parts of an Elisa and what is the importance of each step

Answer 30

Each sample has proteins that will bind to the well Specific antibodies will seek out specific antigens that are bound to the well Wash after every step to remove unbound primary and secondary antibodies, this step prevents false positives from occurring Secondary antibodies Are added and will bind to primary antibodies, wash after this to wash away unbound antibodies Enzyme is added that chemically changes changes the enzyme substrate turning it from colorless to blue False negative could occur if antibody has low specificity or affinity for target antigen Low concentration if antigen may also cause problems when binding to antibody

Question 31

What is an indole test

Answer 31

Tryptophanase breaks down tryptophan into indole, ammonia, and pyruvate If positive it will have red ring and if negative ring will be clear Some rxns test rxn with kovacs reagent because when it mixes with indole it turns red

Question 32

What is the methyl red test

Answer 32

Ph indicator that turns red if acid fermentation has occurred and remains yellow is pH is greater than 6.2 Positive when color is red and negative when color is yellow or clear

Question 33

What is VP test

Answer 33

Used to detect microorganisms that ferment glucose via the butanedoil pathway Positive means red color and pale yellow is negative

Question 34

What is the citrate test

Answer 34

Determines organisms ability to use citrate as sole carbon source Green is negative and blue is positive

Question 35

What is a casein test

Answer 35

Caseinase is an Extracellular enzyme that breaks down casein Put bacteria on skim milk agar plate and if there is a clear ring around the colony this means they can break down casein and result is positive Negative is when there is no ring

Question 36

What is the starch test that uses alpha amylase

Answer 36

Alpha amylase is an enzyme that is secreted by some bacteria to break down starch It’s a polymer of glucose, it’s huge, and needs to be broken down to fit into the cell Put iodine on starch plate and if there is clearing around the colony it means positive result, no clearing stays blue and there is no starch breakdown so no alpha amylase present

Question 37

What is the zone of inhibition

Answer 37

Clearing around the antibiotics where bacteria is either dead or inhibited Measured in mm and just by looking at it you cannot determine if bacteria are dead or inhibited so you must take a swab and grow on separate agar, if they grow the bacteria were just inhibited and not dead

Question 38

What can be determines from a Kirby Bauer test

Answer 38

Determines antibiotic susceptibility for bacteria and allows practitioners to know which antibiotics should be used to treat infection Agar used is mueller Hinton and is non selective so it will not inhibit sulfonamides Based on criteria they can either be resistant, intermediate, or susceptible

Question 39

What is the phenol coefficient

Answer 39

Divide chemical agent dilution by phenol dilution factor This tells how many more times the chemical agent is more effective than the phenol Calculated my comparing concentration that will kill all microorganisms after ten minutes but not five minutes

Question 40

What is a spread plate and how do you use it

Answer 40

Pipet onto agar plate and use spreader to spread the bacteria evenly, lawn of growth should be observed In order to quantify you should know how much you pipet onto the plate and observe thickness of the growth

Question 41

What is a streak plate and what is the dilution technique

Answer 41

Streak the plate with bacteria then sterilize, then streak the plate again using the colony you just put on the plate, sterilize again and streak the plate with the second colony you added to the plate This will create different colonial morphologies

Question 42

What is EMB and what is it defective and differential for

Answer 42

Eosin methylene blue Selective for gram negative because it contains methylene blue and bile salts Differential for acid production from lactose breakdown Neon green metallic color means high production but could also observe pink metallic

Question 43

What is an MSA plate and what is it selective and differential for

Answer 43

Mannitol salt agar plate It is selective for gram positive and contains 7.5 % salt Differential for mannitol sugar fermentation which results in color change, there is a ph indicator present so color will change from pink to yellow if present

Question 44

How do we know if a slide contains an endospore and what stain do we use

Answer 44

Differential stain for spore forming bacteria You will see green spore with a pink layer surrounding it You must steam malachite green stain into the spore in order to see it

Question 45

How do you stain a capsule

Answer 45

Use copper sulfate It will appear as colorless halo around bacterial cell but the cell itself will be pink and background will be dark stain Don’t heat fix as this can compromise the structure