Enterobacteriaceae Part I

Question 1

What are some of the common characteristics of enterobacteriaceae?

Answer 1

They are all gram negative rods that are oxidase negative, catalase positive, facultative anaerobes.They can all fermenrt glucose, and some can ferment lactose (KEE).

Question 2

What is antigenic variation?

Answer 2

When the enterobacteriaceae can switch between the somatic O antigen, capsular K antigen, and flagellar H antigens in order to evade Ab mediated immunity.

Question 3

What are the lactose fermenting enterobacteriaceae?

Answer 3

The KEE organisms (Klebsiella, Escherichia, Enterobacter). Citrobacter also ferments lactose but it is very slow.

Question 4

How do MacConkey and Eosin methylin blue (EMB) media show the presence of lactose fermentation?

Answer 4

If the organism is a lactose fermenter, MacConkey agar will turn pink, and EMB will turn purple. If it is a strong lactose fermenter (like E. coli) then EMB will turn metallic green.

Question 5

What does KIA media tell you?

Answer 5

If the organism can ferment glucose, lactose, and whether it can produce H2S.

Question 6

What does glucose fermentation show up as on KIA agar?

Answer 6

Glucose fermentation turns the KIA agar yellow in less than 24 hours.

Question 7

What is a positive lactose fermentation result for KIA agar?

Answer 7

If it stays yellow for longer than 24-48 hours (will move on to lactose once the glucose is gone). If it is not a lactose fermenter then the agar will turn back to red due to peptone utilization.

Question 8

What is a positive urease test?

Answer 8

If the tube turns orange to pink. If it does not produce urease it will turn from orange to yellow.

Question 9

What are the urease positive enterobacteriaceae?

Answer 9

Proteus (high producer), Klebsiella, and citrobacter.

Question 10

What are the IMViC tests comprised of?

Answer 10

Indole production (SIM media), Methyl red test, Voges-Proskauer test, and citrate production.

Question 11

What does the Vogue-Proskauer test asses?

Answer 11

If the organism can ferment glucose into acetoin and 2,3 butanediol.

Question 12

What is a positive Vogue-Proskauer test?

Answer 12

If the VP reagent is added to MR-VP broth and the organism produces acetoin, then the broth will turn red.

Question 13

What does the Methyl Red test asses?

Answer 13

If the organism uses the mixed acid pathway (lactic acid, acetic acid, ect).

Question 14

What is a positive Methyl Red test?

Answer 14

If the organism produces mixed acids, then the addition of methyl red will keep the MR-VP broth red. If it does not (alkaline environment) then the broth will turn yellow. Note that this is the opposite of phenol red (acids turn it yellow).

Question 15

What is a positive citrase test?

Answer 15

If the simmons citrase agar turns from green to blue.

Question 16

What are the citrase positive organisms?

Answer 16

Citrobacter, Entertobacter aerogenes, Klebsiella, Serratia, adn Salmonella enterica.

Question 17

What is SIM media used to asses?

Answer 17

Indole production, motility, and H2S production.

Question 18

What two organisms produce H2S?

Answer 18

Salmonella and citrobacter.

Question 19

What is a positive Indole test using SIM media?

Answer 19

If Indole is present, adding Kovac’s reagent will turn the SIM media red.

Question 20

How can E. coli be differentiated from the other lactose fermenters i.e. KEE organisms?

Answer 20

E. coli is Indole positive and citrase negative.

Question 21

What are the biochemical tests for E. coli?

Answer 21

E. coli is Methyl red positive, VP negative, oxidase negative, catalase positive, indole positive, citrase negative, and H2S negative.

Question 22

If an E. coli strain possesses type I fimbriae, what are the consequences of this?

Answer 22

It can bind to mannose containing receptors such as uroplatkin and will be more likely to colonize the bladder. E. coli with type I fimbriae are called mannose sensitive.

Question 23

If an E. coli strain possesses P fimbriae (type II or pyelonephritis), what are the consequences of this?

Answer 23

It will be more likely to colonize the urinary tract and cause pyelonephritis. E. coli with P fimbirae are called mannose resistant.

Question 24

What are the tests for Citrobacter?

Answer 24

Motile, citrate positive, Indole negative, VP negative, H2S positive.

Question 25

What infections are Citrobacter associated with?

Answer 25

Hospital acquired infections in neonates and immunocompromised patients. Particularly associated with meningitis and bran abscesses in neonates.

Question 26

What are the tests for Klebsiella pneumoniae?

Answer 26

Lactose fermenter, urease positive, citrate positive, VP positive and methyl red negative.

Question 27

What can the urease activity of Proteus mirabilis cause?

Answer 27

It can result in kidney stones.

Question 28

What are the tests for Proteus mirabilis?

Answer 28

Non-lactose fermenter, Indole negative, Urease positve, H2S positive, VP negative.

Question 29

What two pigments does Pseudomonas aeruginosa produce?

Answer 29

The fluorescent pyoverdin and the blue pyocyanin.

Question 30

What does pyocyanin refer to?

Answer 30

“Blue Pus”, which is characteristic of suppurative infections caused by Pseudomonas.

Question 31

Where is Serratia marcesens usually seen?

Answer 31

It is only seen in the hospital setting (nosocomial)

Question 32

What are the tests for Serratia marcesens?

Answer 32

Non-lactose fermenter, methyl red negative, VP positive, citrase positive.

Question 33

What is relevant about Enterobacter?

Answer 33

It is frequently resistant to multiple antibiotics.

Question 34

What are the tests for Enterobacter?

Answer 34

Lactose fermenter, H2S negative, urease negative, indole negative, VP positive, and citrate positive.