Exercise 30; Enteric bacteria

Question 1

Be able to define enteric

Answer 1

the normal flora and pathogenic bacteria inhabiting the “enteron” or the GI tract

Question 2

What type of media is EMB?

Answer 2

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)

Question 3

What does EMB media contain and what is it used to test for?

Answer 3

Contains Eosin methylene Blue. It is used to isolate gram- enterics from feces. tests for lactose fermenters and gram neg.

Question 4

What types of bacteria does EMB select against?

Answer 4

Selects against gram+ and nonlactose fermenters

Question 5

What does EMB select for?

Answer 5

selects for gram- and lactose fermenters

Question 6

Which one are we specifically growing to get results for EMB?

Answer 6

Gram- lactose fermenters

Question 7

Positive and negative results for EMB agar and what they mean?

Answer 7

positive results- have growth (fermenters- metallic green)

negative results- no color change

Question 8

What type of media is macconkey agar?

Answer 8

a selective and differential media.

Question 9

What does macconkey media contain and what is it used to test for?

Answer 9

contains a neutral dye.

Question 10

What type of bacteria does macconkey select against? Select for? and what are we specifically growing to get results?

Answer 10

selects for gram-, bile and CV inhibit growth of Gram+
differential by looking for lactose fermenters.
bright pink- lactose fermenters
nocolor- nonlactose fermenters

Question 11

Positive and negative results for macconkey agar and what they mean?

Answer 11

Positive results- growth and pink means Lactose fermenters

negative results- colorless nonfermenters of lactose

Question 12

What does the Durham fermentation tube contain and what is it used to test for? Use both caps**

Answer 12

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.

Question 13

WHat is the purpose of the durham tube? which tube contained these?

Answer 13

differential. looking for differences in bacteria fermenting either lactose or glucose.

Question 14

Poitive and negative results for durham fermentation tube and what they mean?

Answer 14

Positive results- 
Lactose creation of gas bubble
change of color from red to yellow (acid)
Negative results-
same red color

Question 15

How does the oxidase test work? What must be in the bacteria to have a positive result?

Answer 15

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.

Question 16

Be able to identify positive results versus negative results and what the results indicate oxidase test

Answer 16

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.

Question 17

Describe what this agar (TSIA) contains and how inoculation is completed

Answer 17

• 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 (??)

Question 18

Be able to identify positive results versus negative results on TSIA and what the results indicate

Answer 18

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

Question 19

What is this media used to detect and how does it work? How is it inoculated? Sulfur Indole motility

Answer 19

• 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

Question 20

Be able to identify positive results versus negative results and what the results indicate sulfur indole motility

Answer 20

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

Question 21

What does Methyl Red test for? Voges Proskauer?

Answer 21

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

Question 22

What is in the medias (MRVP test) and what is being detected?

Answer 22

MR- methylene red detects pH less than 4.

VP- e

Question 23

Be able to identify the results (positive and negative) of these two tests.

Answer 23

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Question 24

What is this media used to detect and how does it work? Urea test

Answer 24

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Question 25

Be able to identify positive results versus negative results and what the results indicate. Urea test

Answer 25

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