What is TSI test used for
Identify enteric bacteria and differentiate them from other gram neg rods
TSIA
Rich medium differentiates glucose fermentation, lactose fermentation, sucrose fermentation and sulfur reduction
What does TSIA include in addition to 3 carbs
Beef extract
Yeast extract
Peptone
Sodium thiosulfate
What is peptone used for
Carbon and nitrogen source
What is sodium thiosulfate used for
Source of reducible sulfur
What is pH indicator in TSIA
Phenol red
What is the hydrogen sulfide indicator in TSIA
The iron in ferrous sulfate
How is TSIA medium prepd
Agar slant with deep butt provides aerobic and anaerobic growth enviornments
How is TSIA slant inoculated
Stab in agar butt followed by fishtail streak of slant
How long is incubation
18-24 hrs for carb ferm
48 hrs for hydrogen sulfide
Saccharolytic
Those organisms capable of breaking glycosidic bonds in carbs
(Sugar+lysis)
TSI yellow slant/yellow butt
Glucose and lactose and or sucrose fermentation with acid accumulation in slant and butt
A/A
What happens when TSI inoculated with glucose only fermenter
Acid products lower pH turn everything yellow I. A few hrs but glucose in short supply(.1) exhausted in 12 hrs
What happens as glucose used up
Reversion, takes 18-24 hrs Organisms located in slant (aerobic region) start to break down available amino acids producing NH3 and raising pH
Where does reversion occur
Only in slant bc of anaerobic conditio s in butt
What does a TSI slant with a red slant and yellow butt after 24 hrs incubation indicate
That organism ferments glucose but not lactose
What color is slant if organisms ferment glucose and lactose
Yellow throughout but bc lactose and sucrose 10 higher conc than glucose, more acid produced and slant and butt stay yellow after 24 hrs
TSI test result red slant/ yellow butt
Glucose fermentation with acid production
Proteins catabolized aerobically (in slant) with alkaline products (reversion)
K/A
TSI test result red slant/red butt
No fermentation
Peptone catabolized aerobically and anaerobically with alkaline oproducts
Not from enterobacteriacae
K/K
TSI test result red slant/no change in butt
Organism is growing slowly or not at all
Not from enterobacteriacae
Nc/Nc
Black precipitate in agar
Sulfur reduction (an acid condition, from fermentation of glucose or lactose and or sucrose, exists in the butt even if the yellow color is obscured by black precipitate
H2S
Cracks in or lifting of agar
Gas production
G
What could happen if read results too early
Early- could show yellow throughout leading you to think org is lactose or sucrose fermenter when it simply may not have gotten rid of glucose yet
Reading after lactose and sucrose depleted
Would show yellow butt red slant so think org is glucose only fermenter
What is purpose of thiosulfate in TSI agar
When bacteria use sodium thiosulfate they can reduce it to sulfite using enzyme thiosulfate reductase and release hydrogen sulfide gas
What is meant by term saccharolytic bacteria. What reaction would it give in TSI tube
Uses all three sugars , glucose, lactose, sucrose
Slant would be yellow bc acid formation from breaking glycosidic binds