The Early Years of Microbiology

Microscopy

Magnifying lenses have been utilized since 1267, the combination of 2 magnifying lenses to form a telescope began in 1608. Turned downward, you might recognize that description as a compound light microscope. Historically the invention of the microscope is disputed but the term microscope 1st comes into use in 1625. Robert Hooke using such a compound scope described "cells" in 1665. However, microscopy and microbiology truly become founded with the development of the first simple microscope by Antone van Leeuwenhoek in 1673.

Antone van Leeuwenhoek, a Dutch linen merchant was likely the first to observe living microbes with his simple microscope containing a single magnifying lens that could magnify 300X. Without knowledge of scientific writing he wrote letters to Henry Oldberg, secretary to the Royal Society of London. Those letters were eventually published in Philosophical Transactions of the Royal Society of London where he described the following:

Protozoa - "animalcules"- Green alga - possibly Spirogyra -red blood cells - spermatozoa

Taxonomy - The Classifiaction of Microorganisms

Initially Developed by Carolus Linneaus - now modified tto be grouped inot 6 broad catagories: bacterai, archaea, fungi, algae, & small multicellular animals. These groups are composed of 2 types of cells>

1. Prokaryotic cells are cells that have no nucleus and no internal membrane bound organelles. The bacteria, blue-green algae (cyanobacteria) and Archaea are all prokaryotic. However, modern classification has demonstrated the Archaea are more closely related to Eukaryotic cells by their nucleic acid (16s rRNA) sequences

a. Bacteria have cell walls composed of peptidoglycan, though some lack cell walls. Archaea lack peptidoglycan with cell walls composed of other chemicals and live in extreme environments of extreme heat and pressure.

2. Eukaryotic cells are cells with a membrane bound nucleus and many internal membrane bound organelles.

a. Fungi, are heterotrophs, meaning they obtain food energy by breaking down organic chemicals. They differ from animal cells as they have cell walls of many different chemical compositions. However, peptidoglycan is unique to bacteria.

Microscopic Fungi consist of yeasts and molds. Yeast are single celled, typically ovoid that reproduce asexualy by a process called budding Molds are fungi composed of elongated cells called hyphae that fuse to form a body called a mycelium. Macroscopic fungi include mushrooms and toadstools all are still heterotrophs composed of hyphae. The body of a mushroom is called the mycelium

b. Protozoa - single celled eukaryotes similar to animals. Most are capable of motility and are initially classified by their locomotive structures, pseudopods, cilia, and flagella. They consist of free living organisms while others are considered parasites.

c. Algae - unicellular to multicellular eukaryotes. Like plants algae are autotrophs, meaning that they do not necessarily require organic energy sources, they can produce their own. Photosynthesis is a common form of autotrophism where the energy from sunlight is used to convert carbon dioxide and water to glucose. Large multicellular algae are seaweeds and kelps.

d. others (animals) parasitic worms l the helminthes - may range in size from microcopic to up to 10 meters in length.

e. viruses - are not composed of cells (acellular). All viruses are obligate intracellular parasites that composed of a protein coat called a capsid and some type of nucleic acid, that may be DNA or RNA but not both. They replicate by using their nucleic acid to "take over" the host cell and inducing it to produce viral progeny.

The "Golden Age" of Microbiology

It was obvious to most scientists and physicians that some agent must be responsible for the spread of infectious disease. Early Greek writings speak of the "Vapours of Disease" blaming the spread of disease on gaseous agents. In 1546 Girolamo Fracastoro published De contagione in which he proposed that infections and epidemics are caused by "seminaria" or the seeds of disease. He may have regarded seminaria as living, but he also compared them to the "exhalations from onions". He even suggested direct contact, airborne and fomites (inanimate objects) as methods to spread disease. This is likely the beginning of the "Germ Theory of Disease" although the theory will remain unproven for more than 300 years.

The use of antiseptics and disinfectants

• 1842 Dr. Oliver Wendell Holmes – observed that mothers of home births had fewer infections than those who gave birth in hospitals and demonstrated that Physician and midwives transferred childbed fever from one mother to another.

1846 Dr. Ignaz Semmelweis – correlated infections with physicians coming directly from the autopsy room to the maternity ward and introduced the use of hypochlorite solutions prevent the spread of disease.

•1867 Joseph Lister – introduced aseptic techniques to reduce microbes in medical settings and prevent wound infections which Involved disinfection of hands using chemicals prior to surgery and the use of heat for sterilization.

Epidemiology

1849 John Snow presented his first observations of the transmission of cholera through drinking water. The epidemic of cholera in India had spread to the Soto district of London. The founder of epidemiology, Snow traced the spread of disease to a single well in the district. Once the handle of the pump was removed the epidemic subsided. His findings were published in a book containing the quantifying data in 1855.

Louis Pasteur Considered the Father of Microbial Methods

1) A French chemist Pasteur was hired by the French wine industry to overcome several years of "bad or sour" wine. He first demonstrated that he could sterilize the brew by boiling it. Note in the middle figure above if he did not break off the the top of the flask it remained clear and free of microbial growth. However, breaking off the top of the flasks allowed the entry of airborne microorganisms and the brew became cloudy. This experiment disproved spontaneous generation of microorganisms (abiogenesis). Although Franciso Redi had disproven spontaneous generation for flies in 1688 other scientists were still presenting evidence of spontaneous generation for microbes.

2) 1857 Pastuer paper outlining the process of microbial fermentation is published in which he showed that sugar fermentation by bacteria led to the production of lactic acid and acetic acid (vinegar) However, fermentation by yeast resulted in the production of alcohol and carbon dioxide and resulted in wine that was not sour. The heating process known a Pasteurization inhibited bacterial growth favoring yeast resulting in the consistent production of "good" wine.

3) Since the acids soured wine Pasteur became a supporter of the Germ Theory of Disease and eventually was able to provide proof of the theory although he was not the first to provide the evidence

4) other contributions included that he coined the term virus, produced the 1st vaccine for rabies, became and early pioneer of virology and immunology and a vaccine for cholera.

The Remaining Problem of Endospores

 

Bacterial endospores are resistance mechanisms that allow bacteria to survive harsh conditions. They are not reproductive structures. The tough layered structure, little free water and no measurable metabolism allow bacteria to resist traditional methods of sterilization and disinfection. Once conditions have resolved to support life the endospores germinate to form a single vegetative cell.

Tyndallization (1876)- British physicist John Tyndall develops the process known as Tyndallization. The process involves heating and cooing a medium over 3 days. Since endospores are resistant to heat and vegetative cells are killed the periods of cooling allow endospores to germinate. Subsequent rounds of heating kill the vegetative cells. Tyndall actually performed these experiments to further disprove spontaneous generation. Society gained another method of sterilization that was also useful in the preservation of foods in canning processes.

In 1877 Ferdinand Cohn demonstrated that the endospores are internal cellular structures.

Proof of the Germ Theory

As the legend is told, Koch used the "jelly from and eyeball" (vitreous humor) as culture medium. The use of semisolid media allow the bacteria to grow in colonies.

Colony - a discrete mass of microbial growth that arises from a single cell. Koch could use thin, sterilized needles to touch a specific colony and transfer it to another sterile medium producing a rapid source of pure culture. Koch published pure culture techniques using gelatin has a solidifying agent in 1881. However, the use of gelatin had limitations.

Walter and Fanny Hesse Agar as a solidifying agent

In another legendary moment in microbiology Koch directed Hesse to find and alternative solidifying agent to replace gelatin as some bacteria digest gelatin liquefying it. Further gelatin melts at incubation temperature losing the advantage of solid medium. Hesse and his wife Fanny improve the plate technique in 1882 with the use of agar to solidify medium.

Agar - a polysaccharide derived from Red Algae (Seaweed) added to media as a solidifying agent. Agar is not digestible by most bacteria and does not liquefy at incubation temperatures. The use of agar provides are more dependable rapid source of pure culture. The use of agar allows the association of many bacteria with specific disease processes in an era known as the "Golden Age of Microbiology"

1774 Sir Edward Jenner and the Process of Science in Immunolgoy Results and the Historical Effect of Vaccination against Smallpox

Although the Chinese had been immunizing individuals against smallpox since about 500 AD, Jenner's work represents the 1st known western scientific study of a vaccine. The Chinese method involved blowing the remnants of the dried scabs of smallpox lesions into the nostrils. Jenner's method proved much safer and effective. Its widespread use led to the declaration of smallpox as a dead disease in the late 1970's illustrating the effectiveness of vaccines against infectious disease

 

 

  

 

A Really Brief History of the Discovery of Viruses

1882- Adolf Mayer - Reports Tobacco Mosaic Disease (TMD) using bacteriological methods reports infectious disease in tobacco plants but is unable to demonstrate any infectious agent. Attributes the disease to an unknown form of a bacterium.

1892 - Dimitry Ivanosky shows that the causative agent of TMD filters through candle fibers known to exclude all bacteria (0.2 um). Without realizing he has discovered an new infectious agent, a virus, Ivanovsky attributes the infectivity to endospores as he remained unaware of Mayer's previous work.

1899 - Martinus Beirjerinck - Independently of Mayer and Ivanosky, Beirjerinck passes the infectious fluid of TMD passed through a porcelain filters and concludes that the infectious is a "non-cellular infectious agent" drawing a strong rebuttal from Ivanosky.

1911 - Francis Peyton Rous - discovers a filterable infectious agent in a solid tumor of chickens, a sarcoma. Almost universally rejected at the time, Rous received the Nobel Prize for his work 55 years later in 1966. Still in 1929 viruses were still defined as filterable infectious agents and not distinguished from Rickettsiae or Spirochete

1940 - the first electron microscope photos of viral particles (bacteriophages) are published.

Events Leading to the Discovery of the Structure of DNA

Bacterial Transformation

In 1928 Frederick Griffith Discovers the phenomenon of bacterial transformation.

Griffith had 2 strains of Streptococcus pneumoniae. In figure (a) the encapsulated strain that he dubbed "S" for it smooth colony was fully virulent killing his experimental mice.

A second strain he name 'r' ( figure b) for its rough colony structure lacked a capsule and was therefore avirulent mice live when injected with the 'r' strain.

figure (c) demonstrated that when the virulent 'S' strain was heat killed mice injected with this preparation lived.

In figure (d) surprisingly when heat killed, avirulent 'S' was mixed with live avirulent 'r' the experimental mice died.Upon necropsy of the and culture of the mice in figure (d) Griffith was able to recover both encapsulated virulent 'S' strand and avirulent 'r' strain that lacked a capsule. Griffith's interpretation was that some compound from the 'S' strain had been transformed to the 'r' strain to convert it into the pathogenic form. He coined the term "transformation". In 1944 Oswald Avery demonstrated that the transforming agent was DNA. Intense study of the DNA molecule ensued.

Rosalind Franklin and Maurice Wilkins and the DNA Helix

James Watson and Francis Crick and the Structure of DNA

 

  

 

 

 

 

 

 

 

 

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