Microbes in our Lives

• Microbiology is the study of living organisms that are too small to be seen with the unaided eye.
• Microorganisms (microbes) are organisms that are too small to be seen with the unaided eye.
• “Germ” refers to a rapidly growing cell.

Microorganisms are important in the maintenance of an ecological balance on Earth.

Some microorganisms live in humans and other animals and are needed to maintain the animal’s health.

Some microorganisms are used to produce foods and chemicals.

Some microorganisms cause disease.

Naming and Classifying Microorganisms

In a nomenclature system designed by Carolus Linnaeus (1735), each living organism is assigned two names.

The two names consist of a genus and a specific epithet, both of which are underlined or italicized. Examples: Escherichia coli or Escherichia coli, Staphylococcus aureus or Staphylococcus aureus.

Types of Microorganisms

Bacteria

Bacteria are unicellular organisms. Because they have no nucleus, the cells are described as prokaryotic.

The three major basic shapes of bacteria are bacillus, coccus, and spiral.

Most bacteria have a peptidoglycan cell wall; they divide by binary fission; and they may possess flagella.

Bacteria can use a wide range of chemical substances for their nutrition.

Archaea

Archaea have prokaryotic cells; they lack peptidoglycan in their cell walls.

Archaea include methanogens, halophiles, and extreme thermophiles.

Fungi

Fungi (mushroom, molds, and yeasts) have eukaryotic cells (with a true nucleus).

Most fungi are multicellular.

Fungi obtain nutrients by absorbing organic material from their environment.

Protozoa

Protozoa are unicellular eukaryotes.

Protozoa obtain nourishment by absorption or ingestion through specialized structures.

Algae

Algae are unicellular or multicellular eukaryotes that obtain nourishment by photosynthesis.

Algae produce oxygen and carbohydrates that are used by other organisms.

Viruses

Viruses are non cellular entities that are parasites of cells.

Viruses consist of a nucleic acid core (DNA or RNA) surrounded by a protein coat. An envelope may surround the coat.

Multicellular Animal Parasites

The principal groups of multicellular animal parasites are flatworms and roundworms, collectively called helminths.

The microscopic stages in the life cycle of helminths are identified by traditional microbiological procedures.

Classification of Microorganisms

All organisms are classified into the Domains Bacteria, Archaea, and Eukarya.

Eukarya includes Protists, Fungi, Plants, and Animals.