The Golden Age of Microbiology Discovering the Cause of Disease Packet #3
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?
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.
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.
Figure 1.10 Redi s experiments.
Does Microbial Life Spontaneously Generate? Needham s experiments Scientists agreed that large animals could not arise spontaneously, but believed microbes could. Needham s experiments with beef gravy and infusions of plant material reinforced this idea.
Does Microbial Life Spontaneously Generate? Spallanzani s experiments His experiments contradicted Needham s findings. Concluded that: Needham failed to heat vials sufficiently to kill all microbes or had not sealed them tightly enough. Microorganisms exist in air and can contaminate experiments. Spontaneous generation of microorganisms does not occur; all living things arise from other living things. Critics said sealed vials did not allow enough air for organisms to survive and that prolonged heating destroyed the life force.
Figure 1.11 Louis Pasteur.
Does Microbial Life Spontaneously Generate? Pasteur s experiments Performed experiments with swan-necked flasks When the 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.
Figure 1.12 Pasteur s experiments with swan-necked flasks.
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 leads to theory/law Disproved hypothesis is rejected or modified
Figure 1.13 The scientific method, which forms a framework for scientific research.
Dr. Bauman s Microbiology Video Tutor For more information, listen to Dr. Bauman describe the steps of the scientific method and discuss several examples.
What Causes Fermentation? Spoiled wine threatened livelihood of many grape growers. Wine makers funded research of methods to promote production of alcohol and prevent spoilage during fermentation. The debate over the cause of fermentation reactions was also linked to the debate over spontaneous generation.
What Causes Fermentation? Pasteur s experiments Some scientists believed air caused fermentation; others insisted that living organisms caused fermentation. Pasteur conducted a series of experiments that addressed the cause of fermentation.
Figure 1.14 How Pasteur applied the scientific method in investigating the nature of fermentation.
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
Table 1.1 Some Industrial Uses of Microbes
What Causes Fermentation? Buchner s experiments Demonstrated fermentation DOES NOT require living cells Showed enzymes promote chemical reactions Buchner s work began the field of biochemistry.
What Causes Disease? Pasteur developed the germ theory of disease. Some diseases caused by specific germs called pathogens
Figure 1.15 Robert Koch.
What Causes Disease? Koch s experiments Robert Koch studied causative agents of disease (etiology). Demonstrated a bacterium causes anthrax Examined colonies of microorganisms
What Causes Disease? Koch s experiments Simple staining techniques First photomicrograph of bacteria First photograph of bacteria in diseased tissue Techniques for estimating bacterial number in a solution Use of steam to sterilize growth media Use of Petri dishes Laboratory techniques to transfer bacteria Bacteria as distinct species
Figure 1.16 Bacterial colonies on a solid surface (agar).
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 to a healthy, susceptible host, the host must get the disease. Same agent must be found in the diseased experimental host.
Table 1.2 Other Notable Scientists of the Golden Age of Microbiology and the Agents of Disease They Discovered
What Causes Disease? Gram s stain The most widely used staining technique One of the first steps to identify a bacterium
Figure 1.17 Results of Gram staining.