Theories for explaining diseases in the past

• Miasma theory: diseases were caused by bad air or miasmas emanating from decaying organic matter, filth, or other noxious environments

  • Diseases like cholera, malaria, and the plague were attributed to miasmas

• Humoral theory: rooted in Greek medicine, this theory was based on the balance of four bodily fluids or humors: blood, phlegm, black bile, and yellow bile. An imbalance among these was believed to cause illness

  • Conditions like fever and inflammation were believed to be due to this

• Contagion theory: diseases could be transmitted from one person to another through direct contact or by touching contaminated objects. This was an early recognition of disease transmission but did not specify the exact nature of the pathogen.

  • Smallpox and syphilis were diseases understood through this theory

• Divine retribution: in ancient cultures, illness was thought to be a form of punishments from deities or a result of supernatural forces. Rituals and prayers were used as cures

  • Leprosy and plagues

• Physiological imbalances: some ancient and medieval theories proposed that diseases arose from internal imbalances unrelated to the humoral theory, such as disturbances in the body’s emotional or physical state

  • Epilepsy

Louis Pasteur (1822-1895)

• Breakthrough from previous theories to germ theory

• Fermentation

  • Was hired by a distillery to study why some wine spoiled into vinegar and other into alcohol

• Founder of bacteriology

  • Isolated microorganisms such as yeasts and bacteria

  • Pasteurization: heating substances between 50-60 degrees C

• Supporter of germ theory

  • Experiments showed that bacteria can cause disease and grow in tissues when placed there

  • Saved the silk industry by discovering Pebrine disease

  • Discovered attenuation that is still used in vaccine development

  • Developed vaccine against anthrax (Bacillus anthracis) and rabies (Lyssavirus)

• Influence

  • One guy (Joseph Lister) believed in Pasteur over the idea that air can carry microorganisms

  • He wanted to kill microorganisms through heat and surgery, but this was a problem because it destroys the skin

Joseph Lister (1860s)

• Founder of modern surgery and movement towards aseptic surgical conditions of today

• Surgical infection might be caused by microorganisms

  • Promoted the idea of sterilizing surgical tools, handwashing, and sterilizing using carbolic acid (phenol)

• Studied wound healing and surgical outcomes

  • Operated under the principles of no germs, no infection, no disease

• Carbolic spray

  • Discovered that carbolic acid destroys microorganisms

  • He gradually decreased carbolic acid to prevent deaths

Ignaz Philipp Semmelweis

• Worked in maternity wards at a time when mortality rates ranges as high as 25-30 percent

• Observed death rate of women in first division of clinic was 2-3 times as high as those in second division

  • Students who did surgeries were taught in first division

  • Midwives worked in the second division

• Ordered students wash their hands in chlorinated lime between examinations with sick and healthy patients

  • Mortality dropped to 1.27 percent

• No one believed him and he died from a wound in custody

Robert Koch (1876, Germany)

• Identified the bacterium responsible for anthrax disease

• Had a feud with Pasteur and thought he was a plagiarist

• Founder of pathogenic microbiology

• Discovered and described the TB bacteria in 1882

  • Challenged the idea that all disease was endogenous (disease came from within and that when you get sick, it was active)

• Inspired a generation of scientists to link disease to the microbes

• Henle-Koch Postulates

  • An organism should be considered that cause of an infectious disease if:

    • It occurred in every case of the disease

    • It can be isolated from diseased patients

    • After isolation and growth in culture, it could produce the same disease when inoculated into a healthy animal model

    • It can be isolated again from the new host

• Methods

  • Take a healthy organism, look at the RBCs, see if positive agent is present, if not, look at diseased organism

• Limitations

  • Some pathogens aren’t easily grown in pure culture (prions)

  • Viruses can’t be replicated purely without a host

  • Causative organism might not be present in every stage of the disease

  • If it is ethically unacceptable to expose a host experimentally to prove the pathogenic relationship or if a model host doesn’t exist

• Spurred the golden age of microbiology and led to discovery of many microorganisms

  • Cholera

  • Leprosy

  • Plague

  • Tetanus

  • Tuberculosis

  • Typhoid fever

  • Diphtheria

Further developments

• Fannie Hesse

  • Credited for suggesting a vegetable-derived jelly could have useful lab applications (agar)

• Julius Richard Petri

  • Petri dish invention

Alexander Fleming (1881-1955)

• Scottish physician scientists

• Studied bacteria, one day a culture of Staphylococci was contaminated with the fungus Penicillium notatum, and noticed how it worked as an antibiotic because it killed part of the bacterial colony

  • Isolated the fungus, put it into a beef broth and started testing it on bacterial colonies

• Shared the Nobel Prize with Howard, Florey, and Ernst Chain in 1945 when the ladder two found a way to produce penicillin in large quantities

Selman Waksman (1888-1973)

• Jewish, ukrainian born American

• Coined antibiotics

• Studied soil bacteria, set out to find as many antibiotics in soil microbes called actinomycetes

• Found antibiotics for

  • Actinomycin

  • Clavacin

  • Streptothricin

  • Streptomycin

  • Grisein

  • Neomycin

  • Fradicin

  • Candicidincandid

Sergei Winogradsky (1856-1953)

• Founder of microbial ecology

  • Studied microbiota of the soil

Frederick William Twort & Felix d’Herelle (1915-1917)

• Discovered bacteriophages

• Twort observed and Herelle named it

Avery, MacLeod, McCarty (1944)

• Discovered DNA

Joshua Lederberg & Edward Tatum

• Bacterial conjugation

Gerald Edelman & Rodney Porter

• Structure of antibodies

Paul Reumeberg

• First recombinant DNA in a tube

Luc Antoine Montagnier & Robert Charles Gallo (1983)

• HIV causes AIDS