Biochemistry I
Labs 22,23,24
Exoenzymes – Lab 22
 Bacteria make enzymes to digest
macromolecules outside of the cell
 The smaller sub units of the enzymatic
reaction are then able to be transported
across the cell membrane
 This capacity is a characteristic of many
Gram Positive bacteria
Hydrolysis of starch
 Starch is composed of glucose molecules connected by
glycosidic linkages
 When the glycosidic linkages are broken, individual sugar
molecules are produced
 Linkages are broken in the presence of Water and the
enzyme amylase
Hydrolysis of Gelatin
 When water and an enzyme are added to a protein,
the peptide bond in proteins are broken, producing
individual amino acids
Gelatin Hydrolysis in the tube
Carbohydrates and Sugars
Glycolysis
Sugar fermentation- Carbohydrate
metabolism
Fermentation
 Phenol red – pH
indicator is red in a
neutral environment
and yellow is the
result of an acidic pH
 Gas – Gas is a by -
product of the
fermentation reaction
-
www.jlindquist.net/generalmicro
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Triple Sugar Iron
 a. metabolize lactose and/or sucrose
b. conduct fermentation to produce acid
c. produce gas during fermentation
d. generate H2S.
TSI Results
Results
BUTT
COLOR/CO
NDITION
Cod
e
Lett
er
Interpretation
Example
RED
R
no fermentation, the bacterium is an
obligate aerobe
Example
red butt
Y
some fermentation has occurred, acid Example
has been produced, it is a facultative yellow
anaerobe.
butt
GAS
FORMED
YG
Seen as cracks in the agar, bubbles,
or the entire slant may be pushed out
of the tube. (Caution: these gassy
fermenters may have bacteria close
to the opening.)
Example
yellow
butt with
gas
BLACK
"+"
H2S has been produced
Example
black butt
YELLOW
SLANT BUTT
H2S
COMMENTS
Shigella
dysenteriae
R
Y
Salmonella
typhimurium
R
YG
+
Causes food poisoning
Salmonella typhi
R
Y
+
Causes typhoid fever
Aerobacter
aerogenes
Y
YG
Similar to Klebsiella,but
nonrespiratory
Escherichia coli
Y
YG
Most common of GIflora
Citrobacter
freundii
Y
YG
+
one of "paracolon" group (nonpathogenic)
Proteus vulgaris
Y
YG
+
Causes GU infections, highly
motile
Klebsiella
pneumoniae
Y
R or
YG
Pneumonia in debilitated patients
(nosocomial)
Pseudomonas
aeruginosa
R
R
GI inhabitant, causes wound, GU
infections
Alcaligenes
faecalis
R
R
GI inhabitant, opportunistic
pathogen of GU
Causes food infection dysentery