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Selective media
Used to inhibit grouwth of some organisms while encouraging the growth of others
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Differential media
Contain indicators to expose differences between organisms
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Eosin Methylene Blue Agar (EMB)
- Contains peptone, lactose, sucrose, eosin Y and methylene blue
- Selective for Gram-negative organisms by inhibiting the growth of gram-positives
- Differential for fermentation
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Mannitol Salt Agar (MSA)
- Contains mannitol, 7.5% sodium chloride, and pH indicator phenol red
- Selective by inhibiting gram-negatives
- Differential by favoring the growth of Staphlycoccus and used to differentiate S. aureus from other Staph's
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Phenylethyl Alcohol Agar (PEA)
- Contains phenylethyl alcohol that interferes with DNA synthesis in gram negatives
- Selective by inhibiting gram-negatives
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MacConkey Agar (MAC)
- Contains lactose, bile salts, neutral red, and crystal violet
- Selective by inibiting gram-positives
- Differential by lactose fermentation
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Blood Agar
- Contains 5% sheep blood in a TSA base
- Differential by ability to hemolyze RBC's
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Zone of Inhibition
No immediate growth aroudn the disinfectant/antibiotic disk
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MIC
Lowest antibiotic concentration that prevents visible bacterial growth
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Penicillin
- Beta-lactam
- Inhibits cell wall synthesis
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Erythromycin
- Macrolide
- Inhibitor of protein synthesis
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Ciprofloxacin
Inhibits DNA replication
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Sulfamethoxazole and TMP
Interuption of metabolic pathways
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MOA of UV
Causes a thymine dimer and bacterial ribosome misreads DNA
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How does bacteria repair after UV exposure?
It makes an enzyme called photolyase that fixes the mutation by using non-uv light
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What organism was used in the UV experiment?
Serratia marcescens
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What was observed with:
no lid?
shade?
lid?
No growth/white colony
No growth under shade
full growth
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Psychrophiles
Optimal 15° C can grow 0° to 20°
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Mesophiles
Grow best at 20° to 40° C
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Thermophiles
Grow above 45°C
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Hyperthermophiles
Grow above 80°C
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What media was used to determine O2 requirements?
Thioglycollate tube
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Obligate aerobes
Need oxygen to grow
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Facultative anaerobes
Will grow anywhere in medium but don't need oxygen
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Obligate anaerobes
Can't grow in oxygen will be at bottom of medium
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Acidophiles
grow well below pH 5.5
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Neutrophiles
will grow between pH of 5.5 to 8.5
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Alkaliphiles
grow well above pH of 8.5
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Phenol Red Durham Tube
Used to determine the ability of some bacteria to ferment a particular carbohydrate has Durham tube in bottom to collect gas bubbles
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What would the results look like in a Durham Tube?
Yellow/no bubbles=Acid/no gas
Yellow/bubbles=Acid/gas
Pink/no bubbles=Alkaline/no gas
Pink/bubbles=Alkaline/gas
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Triple Sugar Iron Tube
- Contains lactose, sucrose, and glucose
- pH indicator is Phenol red
- Purpose of FeSO4 is to see if the organism generate H2S causes black precipitate
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What would results look like in a TSI tube?
Yellow slant/yellow butt=glucose and lactose and/or sucrose were fermented
Red slant/yellow butt=only glucose was fermented
Red slant/red butt=none of the sugars were fermented
Cracks or bubbles in yellow agar=gas was a byproduct of fermentation
Black precipitate formed=H2S was produced
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E. coli
What media will it grow on?
What is the gram rxn?
- EMB(metallic green) and MAC
- Gram-negative
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S. aureus
What media will it grow on?
What is the gram rxn?
- PEA, MSA(yellow), Blood Agar(beta hemolytic)
- Gram-positive
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S. epidermidis
What media will it grow on?
What is the gram rxn?
- PEA, MSA, Blood Agar(gamma hemolytic)
- Gram-positive
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Bacillus subtilis
What media will it grow on?
What is the gram rxn?
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Shigella flexneri
What media will it grow on?
What is the gram rxn?
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Enterobacter aerogenes
What media will it grow on?
What is the gram rxn?
- EMB(lavendar)
- Gram-negative
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