Exercise 30; Enteric bacteria Flashcards
Be able to define enteric
the normal flora and pathogenic bacteria inhabiting the “enteron” or the GI tract
What type of media is EMB?
Selective for gram- bc gram+ can’t grow in methylene blue.
differential by which sugars are fermented
fermenters- metallic green (E. Coli)
nonfermenters- no color change ( salmonella)
What does EMB media contain and what is it used to test for?
Contains Eosin methylene Blue. It is used to isolate gram- enterics from feces. tests for lactose fermenters and gram neg.
What types of bacteria does EMB select against?
Selects against gram+ and nonlactose fermenters
What does EMB select for?
selects for gram- and lactose fermenters
Which one are we specifically growing to get results for EMB?
Gram- lactose fermenters
Positive and negative results for EMB agar and what they mean?
positive results- have growth (fermenters- metallic green)
negative results- no color change
What type of media is macconkey agar?
a selective and differential media.
What does macconkey media contain and what is it used to test for?
contains a neutral dye.
What type of bacteria does macconkey select against? Select for? and what are we specifically growing to get results?
selects for gram-, bile and CV inhibit growth of Gram+
differential by looking for lactose fermenters.
bright pink- lactose fermenters
nocolor- nonlactose fermenters
Positive and negative results for macconkey agar and what they mean?
Positive results- growth and pink means Lactose fermenters
negative results- colorless nonfermenters of lactose
What does the Durham fermentation tube contain and what is it used to test for? Use both caps**
a broth containing sugar (lactose, glucose) and a pH indicator (pheynol- red) that turns from red to yellow, if acid is produced. for gas production a small test tube is submerged upside down in the culture tube. if gas is produced, there will be a bubble in the inverted tube.
WHat is the purpose of the durham tube? which tube contained these?
differential. looking for differences in bacteria fermenting either lactose or glucose.
Poitive and negative results for durham fermentation tube and what they mean?
Positive results- Lactose creation of gas bubble change of color from red to yellow (acid) Negative results- same red color
How does the oxidase test work? What must be in the bacteria to have a positive result?
Works by detecting the electron transport system used in making energy. the paper is a reducing agent that becomes oxidized by the presence of bacteria with an electron transport chain.
Be able to identify positive results versus negative results and what the results indicate oxidase test
Positive result-
sudden purple/ dark blue result in the paper
the paper is a reducing agent that becomes oxidized by the presence of bacteria with an electron transport chain.
Describe what this agar (TSIA) contains and how inoculation is completed
- contains a minimal amount of glucose and excessive amount of lactose and saccharose, pH indicator (pheynol-red), and proteins.
- we inoculate by stabbing and scraping the top.
- looking for changes in fermentation aerobically and anaerobically and the production of H20.
- ferrous sulfate which will oxidize H20 to form iron ppt (??)
Be able to identify positive results versus negative results on TSIA and what the results indicate
positive results-
red slant/ yellow butt- pos for glucose only
yellow slant/butt- pos for glucose and lactose or sucrose
blackening- pos for hydrogen sulfide
Negative Result-
red butt/ slant- neg for all sugars
What is this media used to detect and how does it work? How is it inoculated? Sulfur Indole motility
- Sulfur reduction -break down of proteins
- Indole production -breakdown of proteins
- Motility
- media contains cysteine and bacteria w cysterine disulferase will produce H2S (black)
- media contains tryptophan and bacteria w tryptophase will produce indole which is detected w/kovac
to inoculate we stab once
Be able to identify positive results versus negative results and what the results indicate sulfur indole motility
Positive results-
blackening of agar. production of hydrogen sulfide
indole test- add several drops of kovacs reageant, red color formation is positive.
motility test- cloudiness away from initial stab
What does Methyl Red test for? Voges Proskauer?
MR- detects organisms capable of performing mixed acid fermentation- stable acid that don’t break down further.
VP- used to detect bacteria that convert glucose during fermentation into nonacids (accetonia & 2,3 -butanedid) - VP reagents will oxidize non-acid compounds & will react w/ guanidinenuclei) to produce a red color.
- distinguishing between E.coli and enterobacter
What is in the medias (MRVP test) and what is being detected?
MR- methylene red detects pH less than 4.
VP- e
Be able to identify the results (positive and negative) of these two tests.
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What is this media used to detect and how does it work? Urea test
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