BIMM 121

General Purpose Media

Non-selective, rich (TSA, nutrient broth, TSB)

Selective Media

Kills organisms you don’t want (MacConkey, S. thermophilus agar, MRS)

Enriched Media

Supports organisms you want, enhances the growth of fastidious organisms (S.thermophilus agar, MRS, blood agar)

Differential Media

Distinguishes grown organisms visually (KB media, MacConkey)

What is a MacConkey agar?

A selective and differential media used to isolate gram negative lactose fermentors

What bacteria might be differentiated using MacConkey agar?

Coliform and Enterobacteriaceae

What is in the MacConkey agar that makes it selective?

Bile salt and crystal violet

What is in the MacConkey agar that makes it differential?

Lactose and pH indicator

What is coliform?

gut dwelling bacteria whose presence indicates fecal contamination

Gram Negative

Thin peptidoglycan layer in cell wall surrounded by outer membrane that doesn’t retain crystal violet dye

Gram positive

thicker peptidoglycan layer that holds onto purple stains can retain crystal violet

Cell morphology

size, shape, arrangement

colony morphology

number, color, edges/margins, elevation, texture

What is the purpose of MRS agar

selects lactic acid bacteria

what is the purpose of streptococcus agar

allows streptococcus to grow but not lactobacillus

How does MRS agar work?

Enriched for lactobacillus bulgaricus and selective with a low pH

How does streptococcus agar work?

enriched for streptococcus thermophilus and selective by containing sucrose

What is in milk?

water, proteins, vitamins, lactose fats, and minerals

Streptococcus thermophilus

Gram positive bacteria that contains chains of cocci

lactobacillus bulgaricus

gram positive bacteria that contains chains of bacilli

What do the bacteria in yogurt do and what changes do they cause in the yogurt?

They ferment the lactose into lactic acid causing the pH to lower and casein to denature

How is commercial yogurt made?

Uses defined mixtures and only a few microbes

How is heirloom yogurt made?

By adding old yogurt into new milk

What are probiotics

Live bacteria that provides health benefits when consumed

What is CRISPR

Bacteria’s immune system

What is the goal of the yogurt experiment?

To compare the history of phage infection on the S. thermophilus in commercial and heirloom yogurts

How does CRISPR protect bacteria

It cuts out a small piece of the virus’s genome and inserts it into its own

What is PCR

Polymerase chain reaction used to amplify a small dna segment into millions

What is an amplicon?

the product of PCR

What is an oligo?

A small segment of DNA

What is a primer

starting point for biosynthesis in PCR

Describe the denaturation step

95-98C hydrogen bonds break cause the strands to separate

Describe the annealing step

50-65C where hydrogen bonds form between primers and template

Describe the Extension step

58-72C polymerase finds the ends of the short double stranded DNA regions ofdna where primers are bounded and moves in 5’ to 3’ direction

What is included in the master mix

forward and reverse primers, nucleotide, template, polymerase, and buffer

What is the positive control for the PCR experiment?

S. thermophilus colony from pure culture

What are the two controls for light on the microscope?

brightness dial and condenser diaphragm

What is the definition of resolution?

the ability of a microscope to clearly distinguish 2 very small objects that are placed together as two separate entities

What is the definition of parfocal

A specimen in focus at one objective is also in focus at the next with minor adjustments

When do you use brightfield microscopy?

for color and stained samples

When would use phase contrast microscopy?

When viewing live or transparent specimens

Why should wet mounts be fresh?

Lose motility when cover slip is added due to lack of oxygen and evaporation of water

What are the steps f the scientific method?

Preliminary observation, formulate a good scientific question, background, formulate a hypothesis, test, analyze results, report results

What features are needed for a successful clinical trial

need statistical power, placebo controlled, double blind, random assignment

What is in the loading dye

color to track the progress of the gel and glycerol to weigh down the solution

What is in the running buffer

Tris buffer, acetic acid buffer, and EDTA

What does the tris buffer do?

buffers pH and provides ions for current

What does the acetic acid buffer do

buffers pH and provides ions for current

WHat does the EDTA buffer do?

It is a chelator of cations to bind to and prevents DNases from using cations (Mg)