Microbiology Lab Exam #2

blood agar

test for gram + cocci that tests for type of hemolysis

mannitol salt agar plates

test for gram + rods/cocci that distinguishes between Staph species 

3 possible outcomes of blood agar test

1) no results (gamma hemolysis)

2) lyse RBC, greenish/brown appearance (beta hemolysis)

3) lyse & degrade RBC, clearing (alpha hemolysis)

components of mannitol salt medium

mannitol, salt, phenol red

NaCl

inhibits the growth of gram - in mannitol salt test

result of mannitol salt test

bacteria that can ferment mannitol will turn medium YELLOW (ex. S. aureus & B. subtilis)

components of eosin methylene blue medium

protein, lactose, sucrose, eosin Y, methylene blue

eosin Y & methylene blue

dyes used in eosin methylene blue that inhibit the growth of gram +

coliforms

group of bacteria that grow well on eosin methylene blue (ex. E.coli & E. aerogenes)

components of MacConkey agar medium

protein, lactose, neutral red, CV, bile salts

neutral red

indicator for MacConkey agar

CV & bile salts

inhibit the growth of gram + in MacConkey agar

results of MacConkey agar test

Salmonella & Shigella appear translucent/tannish, lactose fermenters will turns red/pink

Salmonella Shigella agar, eosin methylene blue, MacConkey agar

test for gram - rods that differentiates based on lactose fermentation

contents of Salmonella Shigella agar medium

lactose, protein, NaCl, sodium thiosulfate, neutral red, bile salts, brilliant green

bile salts & brilliant green

inhibit the growth of gram + bacteria in Salmonella Shigella agar test

result of Salmonella Shigella test

Salmonella and Shigella appear as translucent/tannish colonies with dark centers, Shigella sonnei is colorless, E. coli is bright red

thiosulfate in Salmonella Shigella

reacts with Fe²+ to produce H²S

Litmus milk test

test for gram + rods that determines fermentation of lactose and coagulate casein

litmus

pH indicator of litmus milk test

2 results of litmus milk test

1) acid produced from fermentation of lactose, pink → white color change

2) casein protein is broken down or modified (clotting at bottom of tube) (proteolyzed and clarifying at the surface)

triple sugar iron 

test for gram + rods that looks at acidity and gas production

causes production of Fe² in TSI test

reaction between H²S & Fe²+, forming black precipitate

Staphylococcus medium 110

test for gram + cocci that determines mannitol fermentation

7.5% NaCl

inhibitor of gram - in SM-110 test

ammonium sulfate

added to SM-110 test to observe gelatinize activity

results of SM-110 test

S.aureus = orange (has mannitol)

S. epi = white 

components of mitis salvarius medium

5% sucrose, CV, tellurite

CV & tellurite

inhibitors of gram - in Mitis Salvarius test

low levels of tellurite in Mitis salvarius

results in P. vulgaris to grow large colonies

DNase 

line inoculation test that determines if the bacteria can degrade DNA

0.1M HCl

used to precipitate DNA in DNase test

result of DNase test

clear zone will form around the growth in the presence of DNase enzyme

nutrient starch

line inoculation test that determines if the bacteria produce Amylase enzyme

components of nutrient starch test

1% starch plate

gram’s iodine

added to nutrient starch plate

results of nutrient starch test

after gram’s iodine is added, clearing around the line means the bacteria is amylase positive

nutrient gelatin

test to determine if culture has gelatinase

results of nutrient gelatin test

if tubes stay liquid (gelatinase +)

if tubes solidify (getalinase -)

Sulfide indole motility test

stab test for gram - bacteria that is used to determine motility and indole production

tryptophan

breaks down and produces indole in SIM test

Ferrous iron

reacts with H²S to form FeS (black precipitate) in SIM test

results of SIM test

tubes should be observed for precipitate, motility, & indole production

tannish yellow = negative

reddish purple = positive

Kovac’s reagent

used in SIM test to test for indole production

phenylalanine 

test for gram - bacteria (specifically Proteus genus) that tests for phenylalanine deaminase

mechanism of PHE test

phenylalanine breaks down, producing ammonia and phenylpyruvic acid (PPA); FeCl³ reacts with PPA

results of PHE test

if phenylalanine is present = dark green

not present = stay tan

lysine decarboxylase

test only used on glucose fermenters that determines if bacteria has lysine decarboxylase, an enzyme that cuts off CO² from amino acids

mechanism of LYS test

0.1% glucose is added & used up by bacteria, pH increases if lysine decarboxylase is present

results of LYS test

positive for lysine = purple/pink

negative = stays yellow

nitrate test

determines if bacteria will use NO³- as a terminal electron acceptor in anaerobic respiration

bromocresol purple

pH indicator in LYS test

3 reagents for NO³- test

nitrate A, nitrate B, zinc

results of NO³- test

red = NO³- is still present

colorless = denitrification occurred (positive result)

rabbit blood

clotting protein for coagulase test

coagulase results

S. aureus (+)

S. epidermis (-)

hydrogen peroxide

used in catalase test to test for degradation of toxic oxygen species

phenol red sugar

test used to determine the production of acids and gas

Simmons citrate

test from gram - rods that determines if citrate is the primary source of carbon

bromothymol blue

pH indicator for citrate test

mechanisms of citrate test

growth increases CO² levels & increases pH

results of citrate test

E. coli = dark green (negative)

E. aerogenes = vivid blue (positive)

methyl red

test for gram - rods to determine mixed acid fermentation

components of methyl red medium

rich in protein and glucose, methyl red is added

results of MR test

E.coli = red

E. aerogenes = not red (-)

Vgoes Proskauer

test for gram - rods to detect the intermediate of alcohol fermentation

acetylmethylcarbinol

intermediate of alcohol fermentation in VP test

mechanism of VP test

VP-A (alpha naphtol) is added, then VP-B (40% KOH) is added & incubated

results of VP test

dark red/purple = positive (E. aerogenes)

no color change = E. coli (negative)

ONPG

test determining if a lactose culture has B-galactosidase

requirements for lactose fermenters

must have lactose permeate and B-galactosidase

mechanism of ONPG test

ONPG is added — if it is broken down, nitrophenol and glucose are produced. Nitrophenol produces color change

results of ONPG test

yellow = positive