A Brief History of Microbiology

1. A Brief History of Microbiology 1

2. The Early Years of Microbiology • What Does Life Really Look Like? • Antoni van Leeuwenhoek • Began making and using simple microscopes • Often made a new microscope for each specimen • Examined water and visualized tiny animals, fungi, algae, and single-celled protozoa: "animalcules" • By end of 19th century, these organisms were called microorganisms; now they are also called microbes

3. Figure 1.1 Antoni van Leeuwenhoek.

4. Figure 1.2 Reproduction of Leeuwenhoek's microscope. Lens Specimen holder

5. Figure 1.3 The microbial world.

6. The Early Years of Microbiology • How Can Microbes Be Classified? • Carolus Linnaeus developed taxonomic system for naming plants and animals and grouping similar organisms together • Leeuwenhoek's microorganisms are now grouped into six categories: • Bacteria • Archaea • Fungi • Protozoa • Algae • Small multicellular animals

7. The Early Years of Microbiology • How Can Microbes Be Classified? • Bacteria and Archaea • Prokaryotic (lack nuclei) • Much smaller than eukaryotes • Found everywhere there is sufficient moisture; some have been isolated from extreme environments • Reproduce asexually • Bacterial cell walls contain peptidoglycan; some lack cell walls • Archaeal cell walls are composed of polymers other than peptidoglycan

8. Figure 1.4 Cells of the bacterium Streptococcus (dark blue) and two human cheek cells. Prokaryotic bacterial cells Nucleus of eukaryotic cheek cell

9. The Early Years of Microbiology • How Can Microbes Be Classified? • Fungi • Eukaryotic (have membrane-bound nucleus) • Obtain food from other organisms • Possess cell walls • Include • Molds – multicellular; grow as long filaments; reproduce by sexual and asexual spores • Yeasts – unicellular; reproduce asexually by budding; some produce sexual spores

10. Figure 1.5 Fungi. Hyphae Spores Budding cells

11. The Early Years of Microbiology • How Can Microbes Be Classified? • Protozoa • Single-celled eukaryotes • Similar to animals in nutrient needs and cellular structure • Live freely in water; some live in animal hosts • Asexual (most) and sexual reproduction • Most are capable of locomotion by • Pseudopods – cell extensions that flow in direction of travel • Cilia – numerous short protrusions that propel organisms through environment • Flagella – extensions of a cell that are fewer, longer, and more whiplike than cilia

12. Figure 1.6 Locomotive structures of protozoa. Cilia Nucleus Pseudopods Flagellum

13. The Early Years of Microbiology • How Can Microbes Be Classified? • Algae • Unicellular or multicellular • Photosynthetic • Simple reproductive structures • Categorized on the basis of pigmentation and composition of cell wall • Scientists and manufacturers use many algae-derived products

14. Figure 1.7 Algae.

15. The Early Years of Microbiology • How Can Microbes Be Classified? • Other Organisms of Importance to Microbiologists • Parasites • Viruses

16. Figure 1.8 An immature stage of a parasitic worm in blood. Red blood cell

17. Figure 1.9 A colorized electron microscope image of viruses infecting a bacterium. Virus Bacterium Viruses assembling inside cell

18. The Early Years of Microbiology • Tell Me Why • Other Organisms of Importance to Microbiologists

19. The Golden Age of Microbiology • Scientists searched for answers to four questions • Is spontaneous generation of microbial life possible? • What causes fermentation? • What causes disease? • How can we prevent infection and disease?

20. The Golden Age of Microbiology • Does Microbial Life Spontaneously Generate? • Some philosophers and scientists of the past thought living things arose from three processes: • Asexual reproduction • Sexual reproduction • Nonliving matter • Aristotle proposed spontaneous generation • Living things can arise from nonliving matter

21. The Golden Age of Microbiology • Does Microbial Life Spontaneously Generate? • Redi's experiments • When decaying meat was kept isolated from flies, maggots never developed • Meat exposed to flies was soon infested • As a result, scientists began to doubt Aristotle's theory

22. Figure 1.10 Redi's experiments.

23. The Golden Age of Microbiology • Does Microbial Life Spontaneously Generate? • Needham's experiments • Scientists did not believe that animals could arise spontaneously, but that microbes could • Needham's experiments with beef gravy and infusions of plant material reinforced this idea

24. The Golden Age of Microbiology • Does Microbial Life Spontaneously Generate? • Spallanzani's experiments • Results contradicted Needham's findings • Concluded that • Needham failed to heat vials sufficiently to kill all microbes or had not sealed vials tightly enough • Microorganisms exist in air and can contaminate experiments • Spontaneous generation of microorganisms does not occur • The debate continued until the experiments conducted by Louis Pasteur

25. Figure 1.11 Louis Pasteur.

26. The Golden Age of Microbiology • Does Microbial Life Spontaneously Generate? • Pasteur's experiments • Performed investigations of spontaneous generation • When the "swan-necked" flasks remained upright, no microbial growth appeared • When the flask was tilted, dust from the bend in the neck seeped back into the flask and made the infusion cloudy with microbes within a day

27. Figure 1.12 Pasteur's experiments with "swan-necked flasks."

28. The Golden Age of Microbiology • Does Microbial Life Spontaneously Generate? • The scientific method • Debate over spontaneous generation led in part to development of scientific method • Observation leads to question • Question generates hypothesis • Hypothesis is tested through experiment(s) • Results prove or disprove hypothesis • Accepted hypothesis can lead to theory/law • Disproved hypothesis is rejected or modified

29. Figure 1.13 The scientific method, which forms a framework for scientific research.

30. The Golden Age of Microbiology • What Causes Fermentation? • Spoiled wine threatened livelihood of vintners • Some believed air caused fermentation; others insisted living organisms caused fermentation • Vintners funded research of methods to promote production of alcohol and prevent spoilage during fermentation • This debate also linked to debate over spontaneous generation

31. Figure 1.14 How Pasteur applied the scientific method in investigating the nature of fermentation.

32. The Golden Age of Microbiology • What Causes Fermentation? • Pasteur's experiments • Led to the development of pasteurization • Process of heating liquids just enough to kill most bacteria • Began the field of industrial microbiology • Intentional use of microbes for manufacturing products

34. The Golden Age of Microbiology • What Causes Fermentation? • Buchner's experiments • Demonstrated fermentation does not require living cells • Showed enzymes promote chemical reactions • Began the field of biochemistry

35. The Golden Age of Microbiology • What Causes Disease? • Pasteur developed germ theory of disease • Robert Koch studied disease causation (etiology) • Anthrax • Examined colonies of microorganisms

36. Figure 1.15 Robert Koch.

37. The Golden Age of Microbiology • What Causes Disease? • Koch's experiments • Simple staining techniques • First photomicrograph of bacteria • First photomicrograph of bacteria in diseased tissue • Techniques for estimating CFU/ml • Use of steam to sterilize media • Use of Petri dishes • Techniques to transfer bacteria • Bacteria as distinct species

38. Figure 1.16 Bacterial colonies on a solid surface (agar). Bacterium 7 Bacterium 6 Bacterium 8 Bacterium 5 Bacterium 9 Bacterium 4 Bacterium 3 Bacterium 10 Bacterium 2 Bacterium 11 Bacterium 1 Bacterium 12

39. The Golden Age of Microbiology • What Causes Disease? • Koch's postulates • Suspected causative agent must be found in every case of the disease and be absent from healthy hosts • Agent must be isolated and grown outside the host • When agent is introduced into a healthy, susceptible host, the host must get the disease • Same agent must be found in the diseased experimental host

41. Figure 1.17 Results of Gram staining. Gram-positive Gram-negative

42. The Golden Age of Microbiology • How Can We Prevent Infection and Disease? • Many great advances in disease prevention came after it was shown that microbes can cause disease • Modern principles of hygiene not widely practiced in the mid-1800s • Healthcare associated infections were common • Six health care practitioners were instrumental in changing health care delivery methods

43. The Golden Age of Microbiology • How Can We Prevent Infection and Disease? • Semmelweis and handwashing • Ignaz Semmelweis required medical students to wash their hands in chlorinated lime water • Resulted in higher patient survival rates • Lister's antiseptic technique • Joseph Lister advanced antisepsis in health care settings • Sprayed wounds, surgical incisions, and dressings with carbolic acid (phenol)

44. The Golden Age of Microbiology • How Can We Prevent Infection and Disease? • Nightingale and nursing • Florence Nightingale introduced cleanliness and antiseptic techniques into nursing practice • Advocated for hospital and public health policy reform • Snow and epidemiology • John Snow mapped cholera epidemic in London in 1854 • His work was the foundation for infection control and epidemiology

45. Figure 1.18 Florence Nightingale.

46. The Golden Age of Microbiology • How Can We Prevent Infection and Disease? • Jenner's vaccine • Edward Jenner developed a vaccine against smallpox • Demonstrated the validity of vaccination • Began the field of immunology • Ehrlich's "magic bullets" • Paul Ehrlich worked to identify "magic bullets" that would destroy pathogens but not harm humans • Discoveries began the field of chemotherapy

47. Figure 1.19 Some of the many scientific disciplines and applications that arose from the pioneering work of scientists just before and around the time of the Golden Age of Microbiology.

48. The Golden Age of Microbiology • Tell Me Why • Some people consider Pasteur or Koch to be the Father of Microbiology, rather than Leeuwenhoek. Why might they be correct?