Microbio lab exam 2 terms

What are the selective media?

Phenylethyl alcohol agar, Mannitol salt agar, Eosin methylene blue agar, and Hekoten enteric agar

What are the differential media for exozymes?

Starch hydrolysis, lipid hydrolysis, casein hydrolysis, and gelatin hydrolysis

What are the differential media used to identify Enterobacteriaceae?

MR-VP test, citrate utilization test, and SIM media

What are the differential media used for respiration and fermintation?

Phenol red fermintation broth, catalase test, oxidase test, and nitrate reduction test

Differential media

include ingredients that allow us to visually distinguish (or differentiate) one group of bacteria from another based on metabolic features

Selective media

contain ingredients that prevent the growth of certain bacteria. For example, media that are selective for Gram-positive bacteria inhibit the growth of Gram-negative bacteria and allow for the growth of Gram-positive bacteria.

What does PEA differentiate between?

inhibits the growth of many Gram-negative and some Gram-positive organisms

What does it mean when there is poor or no growth on a PEA plate?

Organism is inhibited by phenylethyl alcohol; Probable Gram-negative organism 

What does it mean when there is good growth on a PEA plate?

Organism is not inhibited by phenylethyl alcohol; Probable Staphylococcus, Streptococcus, Enterococcus, or Lactococcus 

What does mannitol salt agar select for?

the growth of bacteria that tolerate salty environments. And for those bacteria that can grow in a salty environment, it allows us to differentiate bacteria based on their ability to ferment mannitol

What does it mean when there is poor or no growth on MSA media?

Organism’s growth is inhibited by NaCl; Not a Staphylococcus species

What does it mean when there is good growth on MSA media?

Organism’s growth is not inhibited by NaCl; Staphylococcus is possible, or some other bacterium known to grow well on MSA

What does it mean when the medium becomes yellow or has a halo around bacteria in MSA?

Organism produces acid from mannitol fermentation; Possible pathogenic Staphylococcus aureus

What does it mean when the medium becomes red and there is no halo around bacteria in MSA?

Organism does not ferment mannitol; Organism other than S. aureus

What is the use for Eosin methylene blue agar?

Selects for gram negative bacteria; differential for lactose fermenters

What are the media/reagents for EMB?

Eosin Y, methylene blue, and lactose

What is a positive result for EMB?

Growth (gram negative);

• fast fermenter: dark green to black

• slow fermenter: pink/maroon

What is a negative results for EMB?

No growth (Gram positive)

• non-fermenter: white/colorless

What is the use for Hekoten enteric agar?

Selects for gram-negative bacteria; differential for lactose fermenters

What are the media/reagents for HE agar?

Bile salts, lactose, sucrose, sulfer thiosulfate, and bromothymol blue, and acid fuchsin

What is a positive result for HE?

Growth (gram negative)

• Fermenter: salmon color

What is a negative result for HE?

No growth (gram positive)

• Non-fermenter: blue to blue green

What is the use of the casease test?

Detects if bacteria can break down casein

What is the media/reagents for the casease test?

Milk agar

What is a positive result for casease test?

Clear zone around bacterial growth

What is negative result for casease test?

No clear zone

What is the use of the gelatinase test?

Detects if bacteria can break down gelatin

What are the media/reagents for the gelatinase test

Nutrient gelatin

What is a positive result for the gelatinase test?

Failure to solidify at cold temperatures

What is a negative results of the gelatinase test?

Solid at cold temperatures

What is the use of the lipase test?

Detects if bacteria can break down tributyrin (lipid)

What are the media/reagents of the lipase test?

Tributyrin agar

What is a positive result of the lipase test?

Clear zone around bacterial growth

What is a negative results of the lipase test?

No clear zone

What is the use of the amylase test

Detects if bacteria can break down starch (amylase presence)

What are the media/reagents for the amylase test?

Starch agar and iodine

What is a positive result of the amylase test

Clear zone around bacterial growth after iodine added (amylase present)

What is a negative results of the amylase test

Purple color zone around bacterial growth after iodine added (amylase absent or not detectable)

What is the use of carbohydrate fermentation (phenol red broth)?

Detects if bacteria can ferment different carbohydrates

What are the media/reagents for carbohydrate fermentation?

Durham tube, phenol red broth (pH indicator), Specific carbohydrate being tested (glucose, lactose, sucrose, etc)

What is a positive result for the carbohydrate test?

Yellow broth with or without bubble in tube

What is a negative result for carbohydrate fermentation?

Red broth, no bubble or pink broth, no bubble

What is the use of the nitrate test?

Identifies the way nitrate is reduced in certain bacteria

What are the media/reagents for the nitrate test?

Nitrate reagent A&B and zinc

What is a positive result of the nitrate test?

Red after adding reagents A&B; after added zinc sol’n is colorless

What is a negative results of the nitrate test?

Red after adding zinc

What is the use of the oxidase test

Detecs cytochrome c oxidase activity (all Enterobacteriaceae negative)

What are the reagents/media for the oxidase test?

TMPD

What is a positive result of the oxidase test?

Purple

What is a negative results of the oxidase test?

Colorless

what is the use of the catalase test?

Tests for catalase production

What are the media/ reagents for the catalase test?

Hydrogen peroxide

What is a positive result of the catalase test?

Bubbles produced

What is a negative results of the catalase test?

No bubbles produced

What is the use of the SIM indole test?

Tests for ability to breakdown tryptophan and yield indole

What are the media/reagents used for the SIM indole test?

SIM medium and Kovac’s reagents

What is a positive result of the SIM indole test?

Red layer on surface of deep

What is a negative SIM indole test?

No red layer on surface of medium

What is the use of the SIM sulfur reduction?

test for ability to reduce sulfer to H2S

What are the media/reagents for the SIM sulfur reduction?

SIM medium

What is a positive result for the SIM sulfur reduction?

Black in medium

What is a negative result for the SIM sulfur reduction?

No black in medium

What is the use of the SIM motility test?

Assess motility (flagella)

What are the media/reagents used for the SIM motility test?

SIM medium

What is a positive result of the SIM motility test?

Growth radiating from stab line into surrounding agar

What is a negative results for the SIM motility test?

Growth only at stab line

What is the use for the Methyl red test?

Detects ability to ferment glucose and form mixed acids

What is the media/reagents used in the methyl red test?

MR-VP broth and methyl red

What is a positive result for the Methyl red test?

Red broth

What is a negative results of the methyl red test?

No color change (yellow broth)

What is the use for the Voges-prokauer test?

Detects ability to ferment glucose with acetoin production

What are the media/reagents for the VP test?

MR-VP broth and Barritt’s reagents

What is a positive result for the VP test?

Red broth after VP reagents added

What is a negative results of the VP test?

No color change (yellow broth or copper color)

What is the use of the citrate test?

Detects ability to utilize Citric acid as sole source of carbon

What is the media/reagents used for the citrate test?

Simmon’s citrate agar and bromothymol blue (pH indicator)

What is a positive result for the citrate test?

Medium turns from green to deep blue; or growth with no color change

What is a negative results of the citrate test?

No color change, medium remains dark green; no growth