Microbial World and You Notes

Microbes in Our Lives

• Microorganisms are organisms too small to be seen without magnification.

• "Germ" refers to a rapidly growing cell.

• Most microbes are not pathogenic (disease-causing).

• Microbes decompose organic waste.

• Microbes are producers in the ecosystem through photosynthesis.

• Microbes produce industrial chemicals like ethyl alcohol and acetone.

• Microbes produce fermented foods like vinegar, cheese, and bread.

• Microbes produce products used in manufacturing and treatment, such as insulin.

• Knowledge of microorganisms allows humans to:

  • Prevent food spoilage.

  • Prevent disease occurrence.

  • Use aseptic techniques to prevent contamination in medicine and microbiology laboratories.

Naming and Classifying Microorganisms

• Carolus Linnaeus established the system of scientific nomenclature.

• Each organism has two names: the genus and the specific epithet.

• Scientific names are italicized or underlined.

• The genus is capitalized, and the specific epithet is lowercase.

• Scientific names are "Latinized" and used worldwide.

• Scientific names may be descriptive or honor a scientist.

Scientific Names

• Staphylococcus aureus:

  • Describes the clustered arrangement of cells (staphylo-) and the golden color of the colonies.

• Escherichia coli:

  • Honors the discoverer, Theodor Escherich, and describes the bacterium’s habitat, the large intestine (colon).

• After the first use, scientific names may be abbreviated with the first letter of the genus and the specific epithet:

  • S. aureus is found on the skin, and E. coli is found in the large intestine.

Types of Microorganisms

Bacteria

• Prokaryotic

• Have peptidoglycan cell walls (unique to bacteria).

• Reproduce via binary fission.

• Use organic chemicals, inorganic chemicals, or photosynthesis for energy.

Archaea

• Prokaryotic

• Lack peptidoglycan

• Live in extreme environments.

  • Methanogens

  • Extreme halophiles

  • Extreme thermophiles

Fungi

• Eukaryotes

• Have chitin cell walls

• Use organic chemicals for energy

• Molds and mushrooms are multicellular, consisting of masses of mycelia composed of filaments called hyphae.

• Yeasts are unicellular.

Protozoa

• Eukaryotes

• Absorb or ingest organic chemicals

• May be motile via pseudopods, cilia, or flagella

Algae

• Eukaryotes

• Have cellulose cell walls

• Use photosynthesis for energy

• Produce molecular oxygen and organic compounds

Viruses

• Acellular

• Consist of a DNA or RNA core

• The core is surrounded by a protein coat.

• The coat may be enclosed in a lipid envelope.

• Viruses are replicated only within a living host cell.

Multicellular Animal Parasites

• Eukaryotes

• Multicellular animals

• Parasitic flatworms and roundworms are called helminths.

• Microscopic stages in life cycles.

Classification of Microorganisms

• Three domains:

  • Bacteria

  • Archaea

  • Eukarya

    • Protista

    • Fungi

    • Plantae

    • Animalia

A Brief History of Microbiology

• Ancestors of bacteria were the first life on Earth.

• The first microbes were observed in 1673.

The First Observations

• In 1665, Robert Hooke reported that all living things were composed of little boxes or “cells”.

• In 1858, Rudolf Virchow said “all cells arise from preexisting cells”.

• Cell Theory: All living things are composed of cells and come from preexisting cells.

• 1673-1723, Anton von Leeuwenhoek described live microorganisms from teeth scrapings, rainwater, and his own feces.

The Debate Over Spontaneous Generation

• Spontaneous generation: Living organisms arise from nonliving matter; a “vital force” forms life.

• Biogenesis: Living organisms arise from preexisting life.

Evidence Pro and Con

• 1668: Francisco Redi filled jars with decaying meat.

  • 3 jars covered with fine net: No maggots

  • 3 open jars: Maggots appeared

  • Conclusion: Biogenesis

• 1745: John Needham put boiled nutrient broth into covered flasks.

  • Nutrient broth heated, then placed in sealed flask: Microbial growth

  • Conclusion: Spontaneous generation

• 1765: Lazzaro Spallanzani boiled nutrient solutions in flasks, then sealed flasks.

  • Nutrient broth placed in flask, heated, then sealed: No microbial growth

  • Conclusion: Biogenesis

• 1861: Louis Pasteur demonstrated that microorganisms are present in the air.

  • Nutrient broth placed in flask, heated, not sealed: Microbial growth

  • Nutrient broth placed in flask, heated, then sealed: No microbial growth

  • Pasteur’s S-shaped flask kept microbes out but let air in, supporting biogenesis.

The Golden Age of Microbiology (1857-1914)

• Discoveries included the relationship between microbes and disease, immunity, and antimicrobial drugs, beginning with Pasteur’s work.

Fermentation and Pasteurization

• Pasteur showed that microbes (yeasts) are responsible for fermentation (conversion of sugar to alcohol to make beer and wine).

• Microbial growth also causes food spoilage.

• Bacteria that use alcohol and produce acetic acid spoil wine by turning it to vinegar (acetic acid).

• Pasteur demonstrated that spoilage bacteria could be killed by heat not hot enough to evaporate the alcohol in wine; this is called pasteurization.

The Germ Theory of Disease

• 1835: Agostino Bassi showed a silkworm disease was caused by a fungus.

• 1865: Pasteur demonstrated that another silkworm disease was caused by a protozoan.

• 1840s: Ignaz Semmelwise advocated hand-washing to prevent transmission of puerperal fever.

• 1860s: Joseph Lister used a chemical disinfectant to prevent surgical wound infections, based on Pasteur’s work.

• 1876: Robert Koch proved that a bacterium causes anthrax and provided Koch’s postulates to prove that a specific microbe causes a specific disease.

Vaccination

• 1796: Edward Jenner inoculated a person with cowpox virus, protecting them from smallpox.

• Vaccination is derived from vacca for cow.

• The protection is called immunity.

The Birth of Modern Chemotherapy

• Treatment with chemicals is chemotherapy.

• Chemotherapeutic agents used to treat infectious disease can be synthetic drugs or antibiotics.

• Antibiotics are chemicals produced by bacteria and fungi that inhibit or kill other microbes.

• Quinine from tree bark was long used to treat malaria.

• 1910: Paul Ehrlich developed salvarsan, a synthetic arsenic drug, to treat syphilis.

• 1928: Alexander Fleming discovered penicillin, the first true antibiotic, made by Penicillium fungus, which killed S. aureus.

• 1940s: Penicillin was tested clinically and mass-produced.

Modern Developments in Microbiology

• Bacteriology: The study of bacteria

• Mycology: The study of fungi

• Parasitology: The study of protozoa and parasitic worms

• Recent advances in genomics (the study of an organism’s genes) have provided new tools for classifying microorganisms.

• Immunology: The study of immunity; vaccines and interferons are being investigated to prevent and cure viral diseases.

• Rebecca Lancefield proposed using immunology to identify some bacteria according to serotypes (variants within a species) in 1933.

• Virology: The study of viruses

• Recombinant DNA is DNA made from two different sources. Paul Berg inserted animal DNA into bacterial DNA in the 1960s, causing the bacteria to produce an animal protein.

• Recombinant DNA technology or genetic engineering involves microbial genetics and molecular biology.

Using Microbes

• George Beadle and Edward Tatum showed that genes encode a cell’s enzymes (1942).

• Oswald Avery, Colin MacLeod, and Maclyn McCarty showed that DNA was the hereditary material (1944).

• Francois Jacob and Jacques Monod discovered the role of mRNA in protein synthesis (1961).

Microbes and Human Welfare

Microbial Ecology

• Bacteria recycle carbon, nutrients, sulfur, and phosphorus that can be used by plants and animals.

• Bacteria degrade organic matter in sewage.

Bioremediation

• Bacteria degrade or detoxify pollutants such as petroleum and mercury.

Microbes and Human Disease

• Bacteria were once classified as plants, leading to the term flora for microbes. This term has been replaced by microbiota.

• Microbes normally present in and on the human body are called normal microbiota.

• Normal microbiota prevent growth of pathogens.

• Normal microbiota produce growth factors such as folic acid and vitamin K.

• Resistance is the ability of the body to ward off disease.

• Resistance factors include skin, stomach acid, and antimicrobial chemicals.