Exercise 16 Flashcards
Exoenzymes
Enzymes secreted by the bacterial cell into their surroundings
Exoenzymes allow
Cells to absorb nutrients that are too large to import through the cell wall and plasma membrane
Exoenzyme reactions
Usually hydrolysis to breakdown larger more complex molecules
Amylase
Breaks down carbohydrates
Beta-lactamase
Exoenzyme that breaks down penicillin related antibiotics
Substrates
Molecules that the enzymes act on
Catalase
Breaks down hydrogen peroxide into water and oxygen gas
Gelatinase
Hydrolyzes gelatin, liquifies it
Catalase positive test
Bubbles appear when hydrogen peroxide is added to the bacteria
Catalase controls
S. aureus (+)
Enterococcus faecalis (-)
Gelatinase positive
Liquifies the gelatin after incubation and refrigeration
Gelatinase controls
S. aureus (+)
E. faecalis (-)
Bacteria that ferment carbohydrates
Produce acid and or gas byproducts
Phenol red broth
Carbohydrate depleted medium with the pH indicator phenol red
Is gas produced without acid
No, acid can be produced without gas but not vice versa
3 carbohydrates tested
Glucose, lactose, fructose
Negative control carbohydrate fermentation (all 3)
Pseudomonas aeruginosa
Glucose acid positive control
E. faecalis
Glucose gas positive
E. coli
Acid positive control lactose
E. faecalis
Gas positive control lactose
E. coli
Acid positive control fructose
Serratia marcescens
Gas positive control fructose
E. coli
IMViC
Indole methyl red Vogues-Pasteur citrate
Indole test
Tests for tryptophan hydrolysis
Enzyme that hydrolyzes tryptophan
Tryptophanase
Tryptophan hydrolysis products
Get broken down into indole, ammonia, and pyruvate
Broth for indole test
Indole/tryptone broth, contains high concentration tryptophan
What’s added for indole test
Kovac’S reagent
Positive indole test
When kovac’s is added it reacts with free indole producing a red organic layer at the top
Indole controls
Positive: E. coli
Negative: Enterobacter aerogenes
Methyl red test
Detects mixed acid fermentation
Medium for methyl red test
MR-VP medium containing glucose, peptone, dipotassium phosphate
Methyl red procedure
Methyl red is added 48 hours after incubation and checked for color change
For methyl red color changes if
If pH is 6.4 and below changes to red
Methyl red controls
Positive: E. coli
Negative: E. aerogenes
Vogues-Proskauer test
Detects the production of a non-acid byproduct of glucose metabolism called acetoin
Vogues- Praskauer procedure
Add 2 VP reagents after 48 hours of incubation, wait 30 mins
Positive VP test
Reagents turn the broth pink/red
VP controls
Positive: E. aerogenes
Negative: E. coli
Citrate test
Determines if bacteria can use citrate as its sole citrate source
Media used in citrate test
Simmons citrate agar with bromothymol blue pH indicator
Positive citrate test
Organism produces alkaline products that raise the pH turning the indicator from green to Prussian blue
Citrate controls
Positive: E. aerogenes
Negative: E. coli
