Microbiology Exercises: Algae, Culture Media, and Handwashing

Algae

Belong to the kingdom Protista and are photosynthetic eukaryotes.

Classification of algae

Based on pigments, carbohydrate food reserves, cell wall composition, and habitat.

Economic Importance of Algae

Includes food & nutrients (e.g., iodine, minerals), used as stabilizers & emulsifiers (e.g., in ice cream, salad dressings), gelling agents (e.g., agar for bacterial culture), and red tide caused by an overgrowth of dinoflagellates.

Rhodophyta

Red Algae.

Chrysophyta

Yellow-Green Algae.

Pyrrophyta

Dinoflagellates.

Chlorophyta

Green Algae.

Phaeophyta

Brown Algae.

Culture media

Provide nutrients for microbial growth.

Types of Media Based on Physical State

Liquid (Broth), Semisolid, Solid (Nutrient agar/blood agar for pure culture isolation).

Liquid Media

Nutrient broth for propagation and fermentation studies.

Semisolid Media

Used for bacterial motility tests.

Solid Media

Nutrient agar/blood agar for pure culture isolation.

Agar slant

Hardened at an angle in a test tube.

Agar deep/butt

Hardened in an upright test tube.

Agar plate

Hardened in a Petri dish.

Autoclaving

121°C, 15 psi for 15+ minutes (kills endospores).

Dry-heat sterilization

Used for sterilizing glassware.

UV radiation

Used for surface sterilization.

Handwashing

The most effective way to prevent infections, especially nosocomial infections.

Transient Microbial Flora

Easily removed by washing.

Resident Microbial Flora

More difficult to remove, requires scrubbing.

Proper Handwashing Technique

Scrubbing with soap removes oil and dirt; brushing for 7-8 minutes maximizes microorganism removal.

Cultural characteristics

Help identify bacterial species.

Gram staining

Differentiates bacteria into Gram-positive (retains crystal violet, purple color) and Gram-negative (stains pink/red with safranin).

Gram-positive

Bacteria that retains crystal violet and appears purple.

Gram-negative

Bacteria that stains pink/red with safranin.