Microbio Lab 2

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Lab 12: bacteriostatic

Back 1

capable of stopping the growth of bacteria

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Lab 12: bactericidal

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capable of causing bacterial cell death

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Lab 12: Disinfectants

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chemical agents used on nonliving surfaces

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Lab 12: Antiseptics

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chemical agents gentle enough to be used on living tissues.

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Lab 12: Why is Gram negative more resistant than gram positives to chemical control agents. Give an example of genus bacteria.

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Gram negative's outer membrane makes it more resistant to chemical control agents.

For ex: Mycobacterium are difficult to control because of their waxy lipid in cell wall. Clostridium for their endospores. Pseudomonas have plasmids that can inactivate many chemical agents.

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Lab 12: What is the oxidizing agents we used? And how does it work on bacteria?

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We used Hydrogen Peroxide (H2O2). It pulls electrons off proteins and membranes and cause the bacterial cell to lyse. Also breaks disulfide bonds.

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Lab 12: What is the halogens used? And how does it work on bacteria?

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Bleach and sodium hydrochlorite is what we used. It pulls electrons off proteins and membranes, causing the cell to lyse.

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Lab 12: What is the alcohol used? And how does it work on bacteria?

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Ethanol, isopropanol is what we used. It dissolved lipids in cell membranes and cause proteins to denature.

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Lab 12: What is the phenols used? And how does it work on bacteria?

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We used Amphyl. It denatures proteins and dissolve lipids.

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Lab 12: What were the bacteria used in this experiment?

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Bacillus subtilis (gram + spore former)
E. coli (gram -)

Staphylococcus aureus (gram +)

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Lab 13: UV light can form what covalent bonds?

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They can cause Thymines to covalently bond and create "Thymine dimers".

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Lab 13: Is UV light a weak or strong radiation?

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It is a weak radiation. It's long wavelength makes it difficult to penetrate objects. It can go through cells and membranes.

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Lab 13: How does bacteria decrease UV absorption?

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1. pigmentation

2. capsule

3. spore formation

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Lab 14: Another name for disc diffusion?

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kirby bauer test

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Lab 14: What ager did we use and why?

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Mueller Hinton agar. It doesn't inhibit activity of certain antibiotics.

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Lab 14: Antibiotic Resistant

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-Penicillin will tell you that it works with Gram (+)

-Ampicillin will effect both +/- and inhibit both gram +/-

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Lab 14: What can you not tell by disc diffusion? In other words, what information does it not tell you?

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Doesn't determine MIC (minimal inhibitory concentration). Only E-test determines MIC.

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Lab 15: What are the control for the Pathogenic Cocci experiment?

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Micrococcus luteus, or nonpathogenic selective media.

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Lab 15: Biochemical test growth medium can either be what? Define the two.

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Selective: encourage growth of some bacteria while inhibiting growth of others.

(ex: mannitol salt agar selects for salt tolerant bacteria)
Differential: allows differentiation of two bacteria growing on same plate.
(ex: bacteria can grow on MSA plate, if they can they will ferment mannitol changing from pink --> yellow)

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Lab 15: Mannitol Salt Agar

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-selective and differential

-determine if bacteria can ferment sugar mannitol while in presence of 7% NaCl salt (is the bacteria halogenphile?)
-yellow = positive for mannitol fermentation
-pink = negative for mannitol fermentation

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Lab 15: Glucose Fermentation Test

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-selective is glucose, differential is phenol red

-Red --> yellow = positive for glucose ferm. pH drops, it is acidic.

-Red only = negative for glucose ferm.

-durham tube traps gas bubble

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Lab 15: Esculin Hydrolysis Test

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-converting esculin to esculetin.

-black= positive result

-esculetin reacts with ferric citrate.

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Lab 15: Hemolysis/Blood Agar

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A: Beta
B: Alpha
C: Gamma

Streptococcus produce enzymes that lyse RBC

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Lab 15: Coagulase test

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solid serum = positive

ex: staph. aureus gives you (+) results, staphococcus epidermidis gives you (-) results

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Lab 16: Eosin Methylene Blue Agar (EMB)

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-is selective (lactose) and differential (dye)
-test to see if bacteria can ferment lactose.

-works on enterobacteriacea

-inhibit Gram (+) growth (ex: Serratia, Proteus, Shigella)

-positive ferm = pink colonies (klebsiella, slow ferm)

-vigorous ferm = green (E. coli)

-negative ferm = grey (serratia, proteus, shigella, salmonella)

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Lab 16: MacConkey Agar

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-test for enteric bacteria (gram neg rod)

-selective (lactose, bile salts, crystal violet)

-differentiate ( neutral red)

-positive (lac ferm) = brick red colonies

-negative (no lac ferm)

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Lab 16: Citrate Test

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-Test to see if bacteria can use citrate as a carbon source. Alkaline is produce giving a alkaline pH.

-selective ingredient (citrate), differential (bromthymol blue)

-Green = negative result

-Blue = positive result

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Lab 16: Urease

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-it is a differential test (ph indicator phenol red), to see if bacteria can hydrolyze urea with enzyme urease.
-positive = dark purple due to ammonia production

-negative = yellow

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Lab 16: Liquid medium

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-yellow + gas (durham tube) = positive

-lactose = gas in tube

-glucose = no gas

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Lab 16: Sim test

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-SIM (Sulfur - indole - motility)

-motility: growth call “swarming”

-indole: red ring is the presence of tryptophanase

-H2S production: black = positive result, presence of H2S

-(A) E. coli is (-) for black, (+) for indole

-P. mirabilis is (+) sulfur reduction, (+) motility

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What is ELISA?

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-ELISA is a test that use antibody and color change to detect a substance.

2 molecules interact: antibody + antigens

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What is a plaque?

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Clearance of bacteria due to bacteriaphage. Virus kills bacteria population.