DMITRI IVANOVSKY (1864-1920)
Dmitri Ivanovsky was a Russian botanist and one of the founding fathers of the field of virology. He discovered the filterable nature of viruses, which allowed them to pass through porcelain filters that prevented the passage of bacteria. This discovery of his was notable in the field of microbiology because it set the foundation for the development of virology. In 1892, he filtered infectious extract from tobacco plants infected with mosaic disease using bacterial filters (which are sieves that excluded bacteria from samples), and found to his greatest surprise that the filtrate was still fully infectious. It was discovered later that diseases in plants and animals was caused by some submicroscopic agents that were smaller than bacteria, and that were retained in the filtrates after passing through the bacterial filters.
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Dmitri’s work ushered in the field of virology which explained a new type of infectious agents called “viruses” – that are capable of permeating porcelain filters, something which bacteria could never do. Dmitri’s findings were studied further by other scientists like Frederick Loefller (1852 -1915), a German bacteriologist who discovered the organism causing diphtheria (Corynebacterium diphtheriae) and the cause of foot and mouth disease (Aphthovirus). F.D Herelle (1873-1949), a French-Canadian microbiologist and F.W Twort (1877–1950), an English bacteriologist who independently discovered bacterial viruses known as “bacteriophages or phages” were other scientists that built on Dmitri’s research. These scientists discovered that this agent (filterable viruses) was quite different from cellular organisms like bacteria whose structure and development are already known. But in 1935, Wendell Stanley (1904-1971) crystallized virus and found that it is made up of protein and nucleic acids.
PAUL EHRLICH (1854-1915)
Paul Ehrlich was a German physician who pioneered the field of antimicrobial chemotherapy, and also contributed to the fields of immunology and haematology. Ehrlich coined the term “chemotherapy” and also developed the concept of “selective toxicity as it relates to antimicrobial agents in the early 1900s”. Selective toxicity is “the ability of an agent to inhibit or kill pathogenic microorganisms without any untoward effect to the host taking it”. Through his work, Ehrlich showed that antimicrobial agents must be selectively toxic in order to be therapeutically effective for use.
Paul Ehrlich tested large numbers of chemical dyes for over a decade in his quest for a “magic bullet” that would kill only microorganisms, and this led him to discover the first ever effective antimicrobial drug “salvarsan”. Salvarsan is a synthetic arsenic compound which was used as at the time to treat and cure syphilis. Salvarsan (the 606th chemical compound he tried) was the most successful drug for the treatment of the sexually transmitted infection (STI) known as syphilis, and which is caused by the spirochaete, Treponema pallidum. His work in this area laid an important foundation for the era of chemotherapy.
Chemotherapy is the use of chemicals that selectively inhibit or kill pathogens without causing damage to the victim. Ehrlich’s work further made it clear that the causative agents of many illnesses were microorganisms, and that chemicals may exist that kill the microbe, but not the patient, thus curing the illness. The discovery of salvarsan (arsphenamine) as an effective therapeutic agent against T. pallidum infection as at the time, paved the way for the discovery and development of other antimicrobial agents (or chemicals) that can be used to combat infectious diseases.
GERHARD DOMAGK (1895-1964)
Gerhard Domagk was a German pathologist and bacteriologist who reported in early 1930s that prontosil (a red dye used for staining leather) was active against pathogenic Staphylococci and Streptococci in mice. Domagk’s discovery of prontosil was yet another breakthrough in the area of antimicrobial chemotherapy after Ehrlich’s discovery of salvarsan; and this marked the first discovery of sulpha antibiotics, which are chemically synthesized antimicrobial agents. It was later that the two French scientists, Jacques and Therese Trefonel discovered in the same year that prontosil was broken down within the body of the host to sulphanilamide (the active component of sulpha drug) which was the true active factor that exhibited antibacterial activity against pathogenic bacteria.
Domagk was credited with the discovery of Sulfonamidochrysoidine (KI-730) – the first commercially available synthetic antibiotic (which was marketed under the brand name, Prontosil) for which he received the Nobel Prize for Medicine or Physiology in 1939. Sulpha drugs were the first widely used growth factor analogs shown to specifically inhibit the growth of bacteria. Gerhard Domagk’s discovery of the sulpha drugs helped to launch a second wave of research on chemotherapeutic agents – which led to the discovery of other hundreds of new antibiotics for the treatment of several infectious diseases in humans and animals.
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