Micro - Biochemical Testing I Flashcards
TSI, LIA, and MIO are used to identify this family of microbes
Enterobacteriaceae
Why should we use tubed biochemicals over automation (2)?
Automation is expensive
Automation doesn’t always work
All sugar fermenters must by definition be able to ferment this sugar…
Glucose
Sugar content of TSI, LIA, and MIO
TSI = lactose, sucrose, glucose
LIA = glucose
MIO = glucose
pH indicator of TSI, LIA, and MIO
TSI = phenol red
LIA = bromocresol purple
MIO = bromocresol purple
Source of H2S for TSI, LIA, and MIO
TSI = sodium thiosulfate
LIA = sodium thiosulfate
MIO = none
KIA (Kligler iron agar) is similar to this media… The difference between the 2 media is…
TSI
TSI has triple sugar, KIA lacks sucrose
TSI - test for an organism’s ability to utilize these sugars…
Glucose, lactose, and/or sucrose
TSI - test for an organism’s ability to reduce ___ to ___
Sodium thiosulfate
Hydrogen sulfide
How do we inoculate a TSI tube, a LIA tube, and a MIO tube?
TSI and LIA = stab and streak
MIO = stab
TSI - the pH indicator, ___, changes from ___ to ___ if the organism can utilize glucose
Phenol red
Red/pink
Yellow
When should TSI tubes be read?
18-24 hours after inoculation and incubation
What does a glucose ONLY fermenter look like on a TSI tube? Why are the slant and butt those colors?
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
TSI/LIA - a positive result for H2S production is the appearance of…
Black precipitation
Gas production can be seen in this test
TSI
-raised/displaced agar with holes in agar, bubbles
TSI - what does an all yellow tube indicate?
Organism ferments glucose, lactose, and/or sucrose
-lactose/sucrose not distinguishable
TSI - nomenclature
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
TSI - a non-fermenter tube looks like this…
Darker red/red
-due to AA utilization, causes alkaline pH
LIA - what 2 things does the test determine?
Ability of organism to decarboxylate or deaminate lysine
-one or the other, not both
Production of H2S
LIA - what does a decarboxylation reaction look like? Where does the decarboxylation reaction happen in the tube? Is decarboxylation an aerobic or anaerobic reaction?
Purple slant, purple butt (K/K)
-turbid medium, no longer transparent
Butt
Anaerobic reaction
LIA - what does a deamination reaction look like? Where does the deamination reaction happen in the tube? Is deamination an aerobic or anaerobic reaction?
Red slant, yellow butt (R/A)
Slant
Aerobic reaction
LIA - no enzymatic reactions with only glucose fermentation looks like…
Purple slant, yellow butt (K/A)
Explain why decarboxylase is a 2 step reaction?
Glucose breakdown produces acid
Acid triggers decarboxylase enzyme
-butt turns yellow (acidic), then purple (alkaline) again due to decarboxylase
LIA - agar in the butt of the tube must initially change to this color, ___, due to the fermentation of…
Yellow
Glucose
-decarboxylase turns yellow media purple again
MIO - determines 3 things
If organism is motile
If organism has ability to break down tryptophan to indole
If organism has ability to decarboxylate ornithine
MIO - what a positive motility result looks like
Turbid medium away from stab line
MIO - what reagent is added to test for indole? What does a positive indole result look like? What does the positive result mean?
Kovac’s reagent
Red color
Indicates presence of indole; organism has tryptophanase
MIO - what does a negative ornithine test result look like? Why is it this color?
Yellow butt, purple top
Glucose fermentation happening in the butt
- top part exposed to air
- deamination reverts top part back to alkaline
MIO - what does a positive ornithine test result look like? Why is it this color?
Purple butt, purple top
Glucose fermentation turns tube yellow and acidic first, but decarboxylase activates and turns tube purple
MIO - what does a positive ornithine test result mean? Is the pH acidic or alkaline?
Organism can decarboxylate ornithine
Alkaline
Does MIO test for H2S?
No
OF media contains this sugar… What is added to one of the tubes? Why?
Glucose (or dextrose)
Mineral oil
Determines if organism can ferment glucose
OF media - yellow in both tubes indicate… Yellow in the open tube only indicate… No yellow in either tube indicate…
Glucose fermenter
Glucose non-fermenter/glucose oxidizer
Cannot ferment or oxidize glucose
