Micro - Biochemical Testing I

Question 1

TSI, LIA, and MIO are used to identify this family of microbes

Answer 1

Enterobacteriaceae

Question 2

Why should we use tubed biochemicals over automation (2)?

Answer 2

Automation is expensive

Automation doesn’t always work

Question 3

All sugar fermenters must by definition be able to ferment this sugar…

Answer 3

Glucose

Question 4

Sugar content of TSI, LIA, and MIO

Answer 4

TSI = lactose, sucrose, glucose

LIA = glucose

MIO = glucose

Question 5

pH indicator of TSI, LIA, and MIO

Answer 5

TSI = phenol red

LIA = bromocresol purple

MIO = bromocresol purple

Question 6

Source of H2S for TSI, LIA, and MIO

Answer 6

TSI = sodium thiosulfate

LIA = sodium thiosulfate

MIO = none

Question 7

KIA (Kligler iron agar) is similar to this media… The difference between the 2 media is…

Answer 7

TSI

TSI has triple sugar, KIA lacks sucrose

Question 8

TSI - test for an organism’s ability to utilize these sugars…

Answer 8

Glucose, lactose, and/or sucrose

Question 9

TSI - test for an organism’s ability to reduce ___ to ___

Answer 9

Sodium thiosulfate

Hydrogen sulfide

Question 10

How do we inoculate a TSI tube, a LIA tube, and a MIO tube?

Answer 10

TSI and LIA = stab and streak

MIO = stab

Question 11

TSI - the pH indicator, ___, changes from ___ to ___ if the organism can utilize glucose

Answer 11

Phenol red

Red/pink

Yellow

Question 12

When should TSI tubes be read?

Answer 12

18-24 hours after inoculation and incubation

Question 13

What does a glucose ONLY fermenter look like on a TSI tube? Why are the slant and butt those colors?

Answer 13

Yellow butt, red slant

Yellow butt due to glucose fermentation
Red slant due to air reacting with the slant, causing alkaline reactions and changing color back to red

Question 14

TSI/LIA - a positive result for H2S production is the appearance of…

Answer 14

Black precipitation

Question 15

Gas production can be seen in this test

Answer 15

TSI

-raised/displaced agar with holes in agar, bubbles

Question 16

TSI - what does an all yellow tube indicate?

Answer 16

Organism ferments glucose, lactose, and/or sucrose

-lactose/sucrose not distinguishable

Question 17

TSI - nomenclature

Answer 17

A/A - yellow slant, yellow butt = glucose, lactose, and/or sucrose fermentation

K/A - red slant, yellow butt = glucose fermentation only

K/K - red slant, red butt = non-fermenter

H2S - black precipitate in butt

G - gas

• A = acid
• K = alkaline

Question 18

TSI - a non-fermenter tube looks like this…

Answer 18

Darker red/red

-due to AA utilization, causes alkaline pH

Question 19

LIA - what 2 things does the test determine?

Answer 19

Ability of organism to decarboxylate or deaminate lysine
-one or the other, not both

Production of H2S

Question 20

LIA - what does a decarboxylation reaction look like? Where does the decarboxylation reaction happen in the tube? Is decarboxylation an aerobic or anaerobic reaction?

Answer 20

Purple slant, purple butt (K/K)
-turbid medium, no longer transparent

Butt

Anaerobic reaction

Question 21

LIA - what does a deamination reaction look like? Where does the deamination reaction happen in the tube? Is deamination an aerobic or anaerobic reaction?

Answer 21

Red slant, yellow butt (R/A)

Slant

Aerobic reaction

Question 22

LIA - no enzymatic reactions with only glucose fermentation looks like…

Answer 22

Purple slant, yellow butt (K/A)

Question 23

Explain why decarboxylase is a 2 step reaction?

Answer 23

Glucose breakdown produces acid

Acid triggers decarboxylase enzyme

-butt turns yellow (acidic), then purple (alkaline) again due to decarboxylase

Question 24

LIA - agar in the butt of the tube must initially change to this color, ___, due to the fermentation of…

Answer 24

Yellow

Glucose

-decarboxylase turns yellow media purple again

Question 25

MIO - determines 3 things

Answer 25

If organism is motile

If organism has ability to break down tryptophan to indole

If organism has ability to decarboxylate ornithine

Question 26

MIO - what a positive motility result looks like

Answer 26

Turbid medium away from stab line

Question 27

MIO - what reagent is added to test for indole? What does a positive indole result look like? What does the positive result mean?

Answer 27

Kovac’s reagent

Red color

Indicates presence of indole; organism has tryptophanase

Question 28

MIO - what does a negative ornithine test result look like? Why is it this color?

Answer 28

Yellow butt, purple top

Glucose fermentation happening in the butt

• top part exposed to air
• deamination reverts top part back to alkaline

Question 29

MIO - what does a positive ornithine test result look like? Why is it this color?

Answer 29

Purple butt, purple top

Glucose fermentation turns tube yellow and acidic first, but decarboxylase activates and turns tube purple

Question 30

MIO - what does a positive ornithine test result mean? Is the pH acidic or alkaline?

Answer 30

Organism can decarboxylate ornithine

Alkaline

Question 31

Does MIO test for H2S?

Answer 31

No

Question 32

OF media contains this sugar… What is added to one of the tubes? Why?

Answer 32

Glucose (or dextrose)

Mineral oil

Determines if organism can ferment glucose

Question 33

OF media - yellow in both tubes indicate… Yellow in the open tube only indicate… No yellow in either tube indicate…

Answer 33

Glucose fermenter

Glucose non-fermenter/glucose oxidizer

Cannot ferment or oxidize glucose