Lab 6 - MSA, EMB, Phenol red

selective media

something has been added to select for (or against) certain types of groups of bacteria

differential media

the media is enriched which will cause certain organsims to show different reactions, but doesn’t inhibit growth

glycolysis

breaking down simple sugars into pyruvic acids

products:

• 2 Pyruvate molecules

• 2 Net ATP molecules

• 2 NADH molecules

• 2 H⁺ ions and 2 H₂O molecules

lactic acid fermentation

• Streptococcus

• Lactobacillus

• Bacillus

• Humans

saccharomyces (yeast) fermentation

ethanol and CO₂

propionibacterium fermentation

propionic acid, acetic acid, CO₂, and H₂

clostridium fermentation

butyric acid, butanol, acetone, isopropyl alcohol, and CO₂

escherichia and salmonella fermentation

ethanol, lactic acid, succinic acid, acetic acid, CO₂, and H₂

enterobacter fermentation

ethanol, lactic acid, formic acid, butanediol, acetoin, CO₂, and H₂

end products of fermentation

help identify microbes, including pathogen in clinical specimens

presumptive

the first test (often done to test for fecal coliforms) to see if lactose fermenting bacteria are present

confirmatory

if the bacteria can ferment lactose, then a second test like the EMB agar can be done to determine if E.coli is present

phenol red lactose broth

a differential fermentation broth that carbohydrates can be added to (glucose, lactose, sucrose)

yellow phenol red broth

pH = 6.8

red phenol red broth

pH = 6.9 -7.4

pink / light purple phenol red broth

pH = above 7.4

fecal coliforms

bacteria that live in the GI tracts of warm blooded animals

• many are gram(-) rods

• most can ferment sugars found in the GI tract

• contamination of food or water poses serious health risks

• ex.) Escherichia coli and Klebsiella aerogenes

Eosin Methylene Blue Agar (EMB)

both selective and differential

• inhibits growth of gram(+) bacteria

• differentiates between coliforms that don’t ferment lactose and those that do

  • fermentation created an acid by-product which makes the eosin change color

EMB strong lactose fermenters

grow and make metallic green colonies

EMB non lactose fermenters

grow, but will be clear (or a faint pink / purple color)

EMB weak lactose fermenters

grow and make bubble gum pink colonies

EMB gram(+)

will NOT grow, inhibited by dye

Klebsiella aerogenes

• gram(-) rod shaped bacteria

• facultative anaerobe

• oxidase negative

• catalase postive

• lactose fermentation: a/g

• commonly resides in soil, water, dairy products, and inhabits natural flora in the GI tract of animals and humans

• HAI: antibiotic resistant, UTI, pneumonia, sepsis, meningitis, and wound or surgical site infections

Staphylococcus aureus

the most pathogenic kind of staph

• infects skin, respiratory tract, digestive tract, brain, etc.

• can release hemolysins which break down RBC

• can release exotoxins that kill WBCs, cause clots, or toxic shock syndrome

MRSA

methicillin resistant staph aureus

• type of staph with penicillin resistant plasmid

• can be HAI or CAI

Mannitol Salt Agar (MSA)

both selective and differential

• typically contains 7.5 - 10% NaCl which inhibits most bacteria from growing

  • staph are halophiles (salt lovers) and can grow in high salt environment

• contains mannitol (sugar alcohol) and phenol red (pH indicator)

  • staph aureus can ferment mannitol into acid which changes the shape