Enterobacteriaceae

Question 1

What does the Vitek system measure? What organisms does it measure?

Answer 1

microbial identification and antibiotic susceptibility testing

a suspension of the test organism is prepared in saline, test cards are then utilized based on testing needs

Strep, Staph, GNB, enterococci, and yeast

Question 2

What kinds of organisms does API 20E measure?

Answer 2

Gram negative, oxidase NEG bacteria

Question 3

How does the Maldi-ToF work?

Answer 3

mass spectrometry: chemical compounds are ionized into charged particles and the ratio of their mass to charge is measured.

MALDI-TOF stands for matrix-assisted laser desorption ionization and Time of Flight, where the time for required for ions to travel the length of the flight tube is measured and can be used to generate a characteristic spectrum based on the mass to charge ratios of proteins and peptide fragments.

Question 4

How does MicroScan work?

Answer 4

Automated program for IDing bacteria by use of simultaneous inoculation of all 96 wells of the panel

Question 5

What 4 enterobacteriaceae are H2S producers?

Answer 5

some Provedencia spp.
Edwardsiella tarta
Salmonella spp.
Proteus spp.

Question 6

What two things make up lactose, and what two things are needed for utilization?

Answer 6

Glucose and galactose

needs permease and beta-galactosidase

Question 7

ONPG is similar to lactose, except it’s made from galactose and what other thing? Does it require permease?

What is a positive color, and what’s a negative one?

Answer 7

made from galactose and orthonitrophemol

Only uses beta-galactosidase

Pos: yellow
Neg: no color change

Question 8

What 8 media have a H2S system?

Answer 8

Salmonella-Shigella
XLD
Hektoen Enteric
BS
KIA
LIA
TSI
SIM

Question 9

KIA detects for the fermentation of what two sugars? What do K and A stand for, what are the colors associated with each, and what do K/A, A/A, and K/K mean?

Answer 9

looks for glucose and lactose only

K = alkaline (red)
A = acid (yellow)

K/A = glucose fermented (yellow butt) and lactose did not (red slant)

A/A = both glucose and lactose fermented (yellow slant and butt)

K/K or K/NC = no glucose or lactose fermentation

Question 10

(What are the A/A organisms on KIA?)

Answer 10

E. coli, Klebsiella spp., Enterobacter spp., (and some Citrobacter)

Question 11

(What are the K/A organisms on KIA?)

Answer 11

Shigella, Salmonella, Serratia, Proteus, Providencia, Morganella, Edwardsiella, Y. enterocolitica and some Citrobacter spp.

Question 12

How is the TSI agar different than the KIA agar? What does this mean for the K/A KIA reactions, and which 3 organisms rxns will now be A/A on TSI?

Answer 12

TSI looks for glucose, lactose, and also sucrose

Some glucose fermenters/non-lactose fermenters on KIA (K/A) will now be A/A in TSI due to being sucrose fermenters

S. marcescens
Y. entercolitica
P. vulgaris

Question 13

What enzyme do some organisms possess to make an indole positive reaction?

Answer 13

They have tryptophanase (which breaks down tryptophan into indole)

Question 14

There are two indole methods: tube test and spot test. What is the reagent for each?

Answer 14

Tube: p-dimethylaminoBENZaldehyde

spot: p-dimethylaminoCINNAmaldehyde

Question 15

What does the methyl red (MR) and Voges-Proskaur (VP) tests analyze? What are the two pathways?

Answer 15

looks for the way Enterobacteriaceae metabolize pyruvate

two pathways to do this:
- mixed acid pathway
- acetoin / butylene glycol

MR: looks for mixed acid
VP: looks for acetoin

(Enterobacteriaceae are usually pos for one or the other, but not both)

Question 16

What does the citrate test look for? What does a positive result look like?

Answer 16

If an organism can use citrate as its only source of carbon

Growth and blue-colored slant is pos

(No growth and green slant is neg)

Question 17

What does lysine iron agar (slant) look for? What do A, K, and R mean? What does H2S look like?

Answer 17

Determines if an enteric decarboxylates or deaminases lysine

A = Acid (yellow)
K = alkaline (purple)
R = deamination (red)

H2S production = black

Question 18

What are the biochemical results of a LIA slant look like/mean? (K/K, R/A, K/A)

Answer 18

So glucose ferments and turns the butt yellow (acid).

Then if lysine is decarboxylated: the whole tube is alkaline aka purple (K/K)

If lysine is deaminated: only the slant turns red and the butt remains acidic aka yellow (R/A)

If lysine is neither decarboxylated or deaminated, the slant is alkaline and butt is acidic (K/A)

Question 19

What is looked for in the urease test? Pos and neg colors?

Answer 19

Looks for enzyme urease that is able to turn urea to ammonia

Pos: pink/red color
Neg: yellow

Question 20

What is a strong urease producer ion Stuart’s urea broth?

Answer 20

Proteus spp.

Question 21

what does the oxidase test look for, and what two spp. of stool bacteria are oxidase positive?

Answer 21

determines whether an organism possesses the cytochrome c oxidase enzyme

Aeromonas spp.
Campy spp.