Midterm Review Powerpoints

What type of media is nutrient agar?

enrichment

What does nutrient agar do?

grows microbes efficiently without inhibiting any growth

What kind of media is EMB?

selective and differential

What does EMB do?

select for gram negative bacteria and differentiates coliforms

What are coliforms?

gram-negative, non-spore forming bacilli

What dyes are in EMB?

eosin and methylene blue

Describe pH properties of EMB

if lactose is fermented, acid is released and the pH goes down; if lactose is not fermented, proteins will be deaminated and the pH goes up

What happens to E. coli on EMB?

turns metallic green

How do you read an EMB plate?

no growth is gram positive, colorless colonies means not a coliform, purple-black colonies means coliform

What type of media is MSA?

selective and differential

What does MSA do?

selects staphylococcus and micrococcus species and differentiates ability to ferment mannitol

Can staphylococcus ferment mannitol?

most pathogenic species can

What is the indicator of MSA?

phenol red; if mannitol is fermented, acid is released and the pH goes down; if mannitol is not fermented, proteins will be deaminated and the pH goes up

What is the salt concentration of MSA?

around 7.5%

How do you read MSA plate?

no growth means not staphylococcus or micrococcus, growth on red plate means non-pathogenic staphylococcus or micrococcus, growth on yellow plate means pathogenic staphylococcus or micrococcus

What type of media is OF glucose?

differential

What does OF glucose do?

differentiates between a bacteria’s ability to break down glucose thorugh fermentation or oxidation

What is the indicator of OF glucose?

bromothymol blue; if glucose is catabolized, acid is released and the pH goes down; if glucose is not catabolized, peptone will be utilized and the pH goes up

Why do you need to use mineral oil in OF glucose test?

for anaerobic conditions; need to do this and normal for each bacteria

How do you read an OF glucose tube with mineral oil?

yellow is acid byproduct and catabolized glucose; no growth is organism needs oxygen and can’t ferment

How do you read an OF glucose tube without mineral oil?

yellow is acid byproducts and catabolized glucose (can metabolize via oxidation or fermentation); teal/blue is ammonia byproduct (organism catabolized peptone and can’t use glucose at all)

What type of media is fermentation tubes?

differential

What does fermentation tubes do?

determines if a bacteria can catabolize a certain carbohydrate (can use different types of carbohydrates)

What is the indicator for fermentation tubes?

phenol red; if carbohydrate is fermented, acid is released and the pH goes down; if carbohydrate is not fermented, proteins will be deaminated and the pH goes up

What does Durham tube tell us in fermentation tubes?

gas is produced and is a true fermenter

How do you read a fermentation tube?

if tube is red, bacteria is a non-fermenter; if tube is yellow with no gas, bacteria is a fermenter; if tube is yellow with gas, bacteria is a true fermenter

What type of media is MRVP broth?

differential

What does MRVP broth do?

determines if acid produced by bacteria is stable or unstable (unstable converted to acetoin)

What does MRVP need in order for results to be read?

needs either methyl red or VPI and VPII to see results

How do you read methyl red tube?

if media turns red, that means the stable acid was produced and the test is positive; if the media does not turn red, that means the stable acid was not produced

How do you read the VP test?

if media turns red, acetoin (unstable acid) was produced and the test is positive; if media does not turn red, that means acetoin was not produced and the test is negative

What type of media is the citrate test?

differential

What does the citrate test do?

detects the production of citrate permease to see if some bacteria can use citrate as a source of carbon

What is the indicator of the citrate test?

bromothymol blue; if citrate is catabolized, ammonia is released and the pH goes up; if citrate is not catabolized, the pH will remain the same

How do you read a citrate test?

if the media turns bleu, that means the citrate was used meaning test was positive; if media remains green, that means the citrate was not used and the test is negative

What type of media is the oxidase test?

differential

What does the oxidase test do?

detects cytochrome C

How do you read an oxidase test?

if the oxidase strip turns blue or purple after a couple of minutes, the test is positive; if the oxidase strip does not change color, the test is negative

What type of media is the catalase test?

differential

What does the catalase test determine?

if the bacteria can produce catalase

Why can’t we use a metal loops to transfer bacteria onto the slide for the catalase test?

because many things have various enzymes that can affect the test

How do you read a catalase test?

if bubbles begin to form, the test is positive; if bubbles do not begin to form, the test is negative

What type of media is nitrate broth?

differential

What does nitrate broth test do?

determines if bacteria produces nitrate reductase

What do you need to be able to read a nitrate test?

reagents A and B; may or may not need zinc powder

How do you read a nitrate broth test?

if you add reagents A and B and it turns red, bacteria reduced nitrate; if not, add zinc powder; if after it turns red, nitrate was reduced by zinc and not the bacteria; if clear after zinc addition, bacteria reduced nitrate to either nitrous oxide or nitrogen gas

What kind of media is gelatin hydrolysis?

differential

What does gelatin hydrolysis do?

determines if bacteeria can catabolize gelatin with use of gelatinase (proteolytic exoenzyme)

How do you read a gelatin hydrolysis test?

if gelatin liquifies, the test is positive; if gelatin is solid, the test is negative

What type of media is a starch plate?

differential

What does starch plate do?

tests for production of amylase

What is amylase?

exoenzyme in our saliva that breaks starch down into glucose

Why do we need to use iodine to read a starch plate?

iodine and starch create a charge-transfer complex, causing the starch to become very dark; if there is a clearing around the bacteria, that means the starch was broken down into glucose and there was nothing for the iodine to bind to

How do you read a starch plate?

after the iodine is poured, if there is a clearing around the bacteria then amylase was produced; if there is no clearing, then amylase was not produced

What type of media is spirit blue agar?

differential

What does spirit blue agar do?

determines if the bacteria can produce lipase

How do you read spirit blue agar?

if triglycerides are broken down into fatty acids at a high rate, bacteria colonies will develop a dark blue participate around edges; a weaker but still positive reaction will create a halo affect around the colonies; a negative result will have normal growth with no changes to the medium around it as the triglycerides remain intact

What kind of media is tryptone broth (indole test)?

differential

What does tryptone broth do?

determines if bacteria produces tryptophanase which turns tryptophan into indole

What do you need to add to tryptone broth to see the results?

Kovac’s reagent

How do you read a tryptone broth test?

if a red/pink ring is present, then indole is present and the test is positive; if a red/pink ring is not present, then indole is not present and the test is negative

What kind of media is the urease test?

differential

What does the urease test do?

determines if a bacteria produces urease and breaks down urea

What is the indicator in urease test?

phenol red; pH dependent; if bacteria produces urease, ammonia will be released and the pH increases; if it does not, the pH will not change

How do you sterilize urease broth?

cannot be autoclaved, needs to be sterilized with vacuum filter

How do you read a urease test?

if media remains the same color, the test is negative; if the media turns fuchsia, the test is positive

What type of media is the phenylalanine slant?

differential

What does the phenylalanine slant do?

determines if bacteria can deaminate phenylalanine; removal of the amine group creates ammonia and creates phenylpyruvic acid as a byproduct

What do you use to see the results of the phenylalanine slant?

ferric chloride

How do you read the results of phenylalanine slant?

if medium turns green, the ferric chloride reacted with the phenylpyruvic acid and the test is positive; if the medium does not change color; no phenylpyruvic acid was produced and the test is negative

What type of media is the SIM test?

differential

What does the SIM test do?

determines if bacteria can release hydrogen sulfide, produce indole, and have motility

How do you read the sulfide production of the SIM test?

if the media has a black precipitate, the test is positive; if the media does not, it is negative

How do you read the indole production of the SIM test?

if a red/pink ring is present after addition of Kovac’s, then indole is present; if not, indole is not present

How do you read the motility portion of the SIM test?

if bacteria are moving away from the area of inoculation, the bacteria are motile; if not, the bacteria is not motile