Microorganisms: Beneficial & Harmful

Microorganisms — also called microbes — are living things so tiny you need a microscope to see them. They live almost everywhere on Earth: in soil, water, air, food, and even inside your body. Some microbes help us, while others can make us sick.

The Main Groups of Microbes

• Bacteria — single-celled organisms shaped like rods, balls, or spirals.
• Viruses — even smaller than bacteria; they need a living host to multiply.
• Fungi — includes yeasts and molds; some are microscopic, others grow into mushrooms.
• Protozoa — single-celled microbes that often live in water or soil.

Beneficial Microbes

Many microbes are useful — without them, life as we know it would not work. Yeast helps bread rise and ferments sugar into bubbles. Lactobacillus turns milk into yogurt and cheese. Friendly bacteria in your gut help you digest food and absorb vitamins. Decomposers break down dead leaves and animals so the soil can be reused. Nitrogen-fixing bacteria living on plant roots add the nutrients crops need to grow.

• Yeast — makes bread rise and ferments fruit into juices.
• Lactobacillus — turns milk into yogurt and cheese.
• Gut bacteria — help digest food and protect against illness.
• Nitrogen-fixing bacteria — feed plants by enriching the soil.
• Penicillium — a fungus used to make the antibiotic penicillin.

Harmful Microbes

Some microbes are pathogens — they cause disease. Salmonella in undercooked food can give you food poisoning. The influenza virus brings on the flu. Streptococcus bacteria can cause a sore throat. Athlete's foot is caused by a fungus that grows on warm, damp skin. Washing your hands, cooking food properly, and getting vaccines all help keep harmful microbes away.

• Salmonella — bacteria that cause food poisoning.
• Influenza virus — causes the flu, with fever and coughing.
• Pathogenic E. coli — some strains cause stomach illness.
• Streptococcus — bacteria that can cause sore throat.
• Athlete's foot fungus — causes itchy skin between the toes.