Chapter 1: The Microbial World and You – Introduction to Microbiology

The Microbial World and You

Introduction to Microbes

Microbiology is the study of microorganisms, which are minute living things too small to be seen with the unaided eye. These organisms play essential roles in the environment, industry, and human health.

• Microbe comes from the Latin word germen, meaning "to sprout" or "to germinate." The term "germ" was first used in the nineteenth century to describe rapidly growing cells that cause disease.

• Microorganisms include bacteria, fungi, protozoa, and microscopic algae.

Roles of Microorganisms in Our Lives

Microorganisms are ubiquitous and have both beneficial and harmful effects on humans and the environment.

• Some are pathogenic (disease-producing).

• Decompose organic waste, recycling nutrients in ecosystems.

• Produce oxygen through photosynthesis (e.g., cyanobacteria, algae).

• Manufacture chemical products such as ethanol and acetone.

• Produce fermented foods (e.g., vinegar, cheese, bread).

• Used in manufacturing (e.g., cellulose) and disease treatment (e.g., insulin).

Knowledge of microorganisms allows humans to:

• Prevent food spoilage.

• Prevent disease occurrence.

• Understand causes and transmission of disease to prevent epidemics.

The Human Microbiome

Definition and Importance

The microbiome (or microbiota) refers to the community of microorganisms living in and on the human body. These microbes are essential for maintaining health and preventing disease.

• The human body contains approximately 30 trillion body cells and 40 trillion bacterial cells.

• The microbiome helps maintain good health, prevents growth of pathogenic microbes, and trains the immune system to distinguish threats.

Acquisition and Colonization

• Microbiota are acquired at birth and throughout life.

• Some microbes colonize the body indefinitely; others are transient.

• Colonization occurs only at body sites that provide appropriate nutrients and environment.

Major Microbiome Research Initiatives

• The Human Microbiome Project (started 2007):

  • Determines the makeup of typical microbiota in various body areas.

  • Studies the relationship between changes in the microbiome and human diseases.

• The National Microbiome Initiative (NMI) (started 2016):

  • Explores the role of microbes in different ecosystems.

Naming and Classifying Microorganisms

Scientific Nomenclature

The system of naming organisms was established by Carl Linnaeus in 1735. Each organism has a two-part name: the genus and the specific epithet (species).

• Names are italicized or underlined.

• The genus is capitalized; the specific epithet is lowercase.

• Names are "Latinized" and used worldwide.

• Names may be descriptive or honor a scientist.

Nomenclature Examples

• Escherichia coli (E. coli):

  • Named after Theodor Escherich, the discoverer.

  • Describes the bacterium's habitat—the large intestine (colon).

• Staphylococcus aureus (S. aureus):

  • Describes clustered (staphylo-) spherical (coccus) cells.

  • Refers to gold-colored (aureus) colonies.

Classification of Microorganisms

Modern classification was developed by Carl Woese in 1978, introducing three domains based on cellular organization.

• Classification is based on differences in cell structure, genetics, and biochemistry.

Additional info: The three domains are Bacteria, Archaea, and Eukarya. This system reflects evolutionary relationships among organisms.