# EMB (Eosin Methylene Blue) Agar **Purpose:** Selective and differential medium. * **Selective:** Inhibits Gram-positive bacteria. * **Differential:** Differentiates lactose fermenters. ### Green metallic sheen * Strong lactose fermentation * Classic organism: **E. coli** ### Colony colors * **Green metallic sheen:** Strong lactose fermenter (E. coli) * **Purple/black colonies:** Lactose fermenter (Enterobacter, Klebsiella) * **Colorless colonies:** Non-lactose fermenter (Salmonella, Shigella) --- # MacConkey Agar ### Contains * Lactose * Neutral red indicator * Crystal violet * Bile salts ### Purpose * Selects for Gram-negative bacteria * Differentiates lactose fermenters ### Results **Pink/red colonies** * Lactose fermenter **Colorless colonies** * Non-lactose fermenter --- # TSIA (Triple Sugar Iron Agar) ### Tests for * Glucose fermentation * Lactose fermentation * Sucrose fermentation * Gas production * Hydrogen sulfide (H₂S) ### Sugars present * Glucose (0.1%) * Lactose (1%) * Sucrose (1%) ### Color meanings Yellow = Acid (A) Red = Alkaline (K) Black = H₂S production Cracks/lifting = Gas production ### Interpretations **A/A** * Yellow slant * Yellow butt * Ferments glucose + lactose and/or sucrose **K/A** * Red slant * Yellow butt * Ferments glucose only **K/K** * Red slant * Red butt * No sugar fermentation ### Proper inoculation * Stab the butt once. * Streak the slant as you remove the needle. --- # Mannitol Salt Agar (MSA) ### Purpose Selective and differential. ### Selective * 7.5% salt selects for **Staphylococcus**. ### Differential * Mannitol fermentation ### Results Yellow media * Mannitol fermented * Acid produced Red/Pink media * No mannitol fermentation ### Species **Staphylococcus aureus** * Yellow * Pathogenic **Staphylococcus epidermidis** * Pink/red * Usually non-pathogenic --- # Blood Agar ### Classification **Both enriched and differential** ### Hemolysis **Beta** * Complete hemolysis * Clear zone **Alpha** * Partial hemolysis * Green zone **Gamma** * No hemolysis * No color change --- # Kirby-Bauer Test Purpose: Determine antibiotic susceptibility. ### Measure Diameter of the **zone of inhibition** (mm). Large zone * Sensitive Small/no zone * Resistant --- # UV Light ### Mechanism UV damages DNA by forming **thymine dimers**. ### Most harmful wavelength **254 nm (UV-C)** ### Interpretation Less bacterial growth = UV more effective. --- # Urease Test ### Purpose Detect urease enzyme. ### Reaction Urea → Ammonia + CO₂ Ammonia raises pH. ### Color Pink = Positive Yellow/orange = Negative ### Strong urease-positive genus **Proteus** --- # Catalase Test ### Reagent Hydrogen peroxide (3%) ### Positive Bubbles immediately ### Negative No bubbles Reaction: 2H₂O₂ → 2H₂O + O₂ The bubbles are oxygen gas. --- # Passive (Indirect) Agglutination ### Definition Antibodies bind to antigen-coated particles, causing visible clumping. Positive = Clumping Negative = Smooth suspension --- ## High-Yield Organisms to Memorize | Organism | Key Feature | | ------------------------------ | ------------------------------------------------- | | **E. coli** | Green metallic sheen on EMB | | **Proteus** | Strong urease positive | | **Staphylococcus aureus** | MSA turns yellow (mannitol fermenter) | | **Staphylococcus epidermidis** | MSA stays pink | | **Salmonella** | Non-lactose fermenter; often H₂S positive on TSIA | | **Shigella** | Non-lactose fermenter; H₂S negative | ## Last-minute memorization * **EMB** → Green sheen = **E. coli** * **MacConkey** → Pink = lactose fermenter * **MSA** → Yellow = mannitol fermenter (**S. aureus**) * **Blood agar** → Beta = clear, Alpha = green, Gamma = none * **TSIA** → Yellow = acid, Red = alkaline, Black = H₂S * **Kirby-Bauer** → Bigger zone = more susceptible * **Urease** → Pink = positive (**Proteus**) * **Catalase** → Bubbles = positive * **UV** → 254 nm causes thymine dimers

Newton's First Law of Motion

An object at rest stays at rest, and an object in motion stays in motion unless acted upon by a net external force.

Kinetic Energy

The energy an object possesses due to its motion, calculated as $KE = \frac{1}{2}mv^2$.

Potential Energy

The energy stored in an object due to its position or arrangement, commonly associated with gravitational energy as $PE = mgh$.

Law of Conservation of Energy

The total energy in a closed system remains constant; energy can neither be created nor destroyed.

Work

The transfer of energy that occurs when a force is applied over a distance, calculated as $W = F \times d \times \text{cos}(\theta)$.

Power

The rate at which work is done or energy is transferred, calculated as $P = \frac{W}{t}$.

Friction

A force that opposes motion between two surfaces in contact.

Mass

A measure of the amount of matter in an object, typically measured in kilograms (kg).

Acceleration

The rate of change of velocity of an object, expressed in meters per second squared (m/s²).

Velocity

The speed of an object in a specific direction, calculated as the change in position over time.