BI 234 LAB FINAL PCC EXAM QUESTIONS AND ANSWERS
WITH COMPLETE SOLUTIONS VERIFIED
What are the shapes of bacteria?
circular, rhizoid, irregular, filamentous, spindle
what are the basic stains (positive)
Crystal violet, Safranin, methylene blue (stains organism)
what are the Acidic stains (negative)
Nigrosine, congo red (background is stained)
what is the goal of a Streak plate
goal is to generate isolated colonies from a mixed culture
what is crystal violet used in
primary stain in gram stain and differential stain; stains the cell purple
what is the purpose of iodine
mordant
what is the purpose of Safranin
counterstain
what color is gram + after staining process
Purple and no outer membrane
what color is gram - after staining process
PINK and has outer membrane wall
mordant
,acts as a fixative, sets dye
endospore stain
A differential stain used to detect the presence and location of spores in bacterial cells.
Use of malachite green, safranin
Structure stains
Used to distinguish parts of cells
Capsule stain
Endospore stain
Flagella stain
Citrate test
What is the byproduct of this test
medium used to determine whether an organisms can utilize citrate as its sole carbon
source. As pH goes up, medium changes from green to blue.
Blue = Positive
Green = Negative
by product is Ammonia.
- converting ammonium phosphate to ammonia
hydrolytic enzymes
enzymes that speed up/aid in the breakdown of chemical bonds through the addition of
water (hydrolysis)
Exoenzymes
, enzymes secreted by microbes that break down and inflict damage on tissues. ex:
amylase, lipase, proteases
Urea Hydrolysis Test
Tests the ability of an organism to produce an exoenzyme, called urease, that
hydrolyzes urea to ammonia. Pink = positive, orange= slow urea hydrolysis, yellow =
negative
Gelatin Hydrolysis Test
used to determine the ability of a microbe to produce gelatinases. Gelatinase-positive
organism will liquefy and gelatinase-negative organism will remain solid. Differentiates
S. aureus from S. epidermidis
SIM Medium Test
Sulfur, Indole, and Motility (Indole production by tryptophanase). Differentiate E. coli
from other enterobacteria.
Lysine Decarboxylase Test
detects enzymatic removal of the carboxyl group from lysine
medium becomes more alkaline causing a pH indicator to change color. Purple =
decarboxylation, yellow= fermentation (no decarboxylation), no color change = no
decarboxylation (brown/orange color)
Phenol Red Test
Differential tests for sugar fermentation and gas production (gram- enteric bacteria). 4
tubes: glucose, lactose, mannitol, sucrose. YELLOW below pH of 6.8 and PINK above
pH 7.4
Durham Tube Sugar Fermentation
WITH COMPLETE SOLUTIONS VERIFIED
What are the shapes of bacteria?
circular, rhizoid, irregular, filamentous, spindle
what are the basic stains (positive)
Crystal violet, Safranin, methylene blue (stains organism)
what are the Acidic stains (negative)
Nigrosine, congo red (background is stained)
what is the goal of a Streak plate
goal is to generate isolated colonies from a mixed culture
what is crystal violet used in
primary stain in gram stain and differential stain; stains the cell purple
what is the purpose of iodine
mordant
what is the purpose of Safranin
counterstain
what color is gram + after staining process
Purple and no outer membrane
what color is gram - after staining process
PINK and has outer membrane wall
mordant
,acts as a fixative, sets dye
endospore stain
A differential stain used to detect the presence and location of spores in bacterial cells.
Use of malachite green, safranin
Structure stains
Used to distinguish parts of cells
Capsule stain
Endospore stain
Flagella stain
Citrate test
What is the byproduct of this test
medium used to determine whether an organisms can utilize citrate as its sole carbon
source. As pH goes up, medium changes from green to blue.
Blue = Positive
Green = Negative
by product is Ammonia.
- converting ammonium phosphate to ammonia
hydrolytic enzymes
enzymes that speed up/aid in the breakdown of chemical bonds through the addition of
water (hydrolysis)
Exoenzymes
, enzymes secreted by microbes that break down and inflict damage on tissues. ex:
amylase, lipase, proteases
Urea Hydrolysis Test
Tests the ability of an organism to produce an exoenzyme, called urease, that
hydrolyzes urea to ammonia. Pink = positive, orange= slow urea hydrolysis, yellow =
negative
Gelatin Hydrolysis Test
used to determine the ability of a microbe to produce gelatinases. Gelatinase-positive
organism will liquefy and gelatinase-negative organism will remain solid. Differentiates
S. aureus from S. epidermidis
SIM Medium Test
Sulfur, Indole, and Motility (Indole production by tryptophanase). Differentiate E. coli
from other enterobacteria.
Lysine Decarboxylase Test
detects enzymatic removal of the carboxyl group from lysine
medium becomes more alkaline causing a pH indicator to change color. Purple =
decarboxylation, yellow= fermentation (no decarboxylation), no color change = no
decarboxylation (brown/orange color)
Phenol Red Test
Differential tests for sugar fermentation and gas production (gram- enteric bacteria). 4
tubes: glucose, lactose, mannitol, sucrose. YELLOW below pH of 6.8 and PINK above
pH 7.4
Durham Tube Sugar Fermentation
