UNIT 2: HISTORY OF MICROBIOLOGY & BACTERIAL GENETICS

Unit 2 Overview:

• 1. History of Microbiology• Video• Koch’s postulates

• 2. Bacterial Growth and Metabolism• Growth Requirements for Bacteria• Bacterial Metabolism• Culturing Bacteria and Sterile Technique

• 3. Bacterial Genetics• Central Dogma in Bacteria• Bacterial Transformation• Bacterial Conjugation

HOW DID MICROBIO BECOME A FIELD?

• 1665: Robert Hooke reported that living things were composed of little boxes, or cells

• 1858: Rudolf Virchow said cells arise from preexisting cells

• Cell theory: All living things are composed of cells and come from preexisting cells

Figure 1.2a

The First Observations• 1673-1723: Antonie van Leeuwenhoek described live microorganisms

• http://www.ucmp.berkeley.edu/history/leeuwenhoek.html

Leeuwenhoek’s microscope

The Debate over Spontaneous Generation ( a very long lasting debate….)

• Spontaneous generation: The hypothesis that living organisms arise from nonliving matter; a “vital force” forms life

• Biogenesis: The hypothesis that the living organisms arise from preexisting life

Conditions Results

Three jars covered with fine net

No maggots

Three open jars Maggots appeared

From where did the maggots come?What was the purpose of the sealed jars?Spontaneous generation or biogenesis?

Evidence Pro and Con• 1668: Francesco Redi filled 6 jars with decaying meat

Conditions Results

Nutrient broth heated, then placed in sealed flask

Microbial growth

From where did the microbes come?Spontaneous generation or biogenesis?

Evidence Pro and Con• 1745: John Needham put boiled nutrient broth into covered flasks

Conditions Results

Nutrient broth placed in flask, heated, then sealed

No microbial growth

Spontaneous generation or biogenesis?

Evidence Pro and Con• 1765: Lazzaro Spallanzani boiled nutrient solutions in flasks

Conditions Results

Nutrient broth placed in flask, heated, not sealed

Microbial growth

Nutrient broth placed in flask, heated, then sealed

No microbial growth

Spontaneous generation or biogenesis?

Evidence Pro and Con• 1861: Louis Pasteur demonstrated that microorganisms are present in the air

Figure 1.3

The Theory of Biogenesis

• Pasteur’s S-shaped flask kept microbes out but let air in

The Golden Age of Microbiology

• 1857–1914• Beginning with Pasteur’s work, discoveries included the relationship between microbes and disease, immunity, and antimicrobial drugs

The Germ Theory of Disease• 1835: Agostino Bassi showed that a silkworm disease was caused by a fungus

• 1840s: Ignaz Semmelweis advocated hand washing to prevent transmission of puerperal fever from one OB patient to another

• 1860s: Applying Pasteur’s work showing that microbes are in the air, can spoil food, and cause animal diseases, Joseph Lister used a chemical disinfectant to prevent surgical wound infections

Thomas Eakins

The Gross Clinic 1875 The Agnew Clinic 1889

Lister and Semmelweis

Fermentation and Pasteurization• Pasteur showed that microbes are responsible for fermentation

• Fermentation is the conversion of sugar to alcohol used to make beer and wine

• Microbial growth is also responsible for spoilage of food

• Bacteria that use alcohol and produce acetic acid spoil wine by turning it to vinegar (acetic acid) and bacteria that utilize lactose to produce lactic acid transform milk into yogurt

Figure 1.4

Fermentation and Pasteurization• Pasteur demonstrated that these spoilage bacteria could be killed by heat that was not hot enough to evaporate the alcohol in wine

• Pasteurization is the application of a high heat for a short time

Pasteurization

• Reduces spoilage organisms and pathogens• Equivalent treatments

• 63°C for 30 min• High-temperature short-time: 72°C for 15 sec• Ultra-high-temperature: 140°C for <1 sec• Thermoduric organisms survive

The Germ Theory of Disease

• 1865: Pasteur believed that another silkworm disease was caused by a protozoan

• 1876: Robert Koch proved that a bacterium causes anthrax and provided the experimental steps, Koch’s postulates, to prove that a specific microbe causes a specific disease

Robert Koch (pronounced “coke”)

- German physician and bacteriologist

- Lived 1843-1910

- Developed a criteria for determining whether a given bacteria is the cause of a given disease:

- Known as Koch’s Postulates

The Germ Theory of Disease

Koch’s Postulates

1. The microorganism must be found in all organisms suffering from the disease, but not in healthy organisms.

2. The microorganism must be isolated from a diseased organism and grown in pure culture.

3. The cultured microorganism should cause disease when introduced into a healthy organism.

4. The microorganism must be again isolated from the inoculated, diseased experimental host and identified as identical to the original specific causative agent.

The Germ Theory of Disease

Koch’s Postulates

Figure 14.3

Koch’s Postulates

Figure 14.3

Procedures Overview

Postulate 1

The microorganism must be found in all organisms suffering from the disease, but not in healthy organisms.

1. Compare yogurt and milk and define the symptoms of “yogurtness”:

- microscopic observations- textures, consistency- smell- pH

Milk simulates a “healthy” sample Yogurt simulates a “diseased” sample

The microorganism must be isolated from a diseased organism and grown in pure culture.

Postulate 2

2. Observe the cultures using a microscope and compare the different types of colonies.

3. Inoculate 3 separate petri dishes:

Heathy individual- milk Diseased individual- yogurt Control bacteria- E.coli (control)

4. Grow cultures overnight at 370C

Postulate 3

The cultured microorganism should cause disease when introduced into a healthy organism.

5. Inoculate fresh milk with bacteria colonies from the petri dishes

6. Incubate overnight 370C

7. Assess symptoms of the subject (pH, smell, texture). Are these the same symptoms of “yogurtness”?

The microorganism must be again isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent

Postulate 4

8. Observe yogurt and milk under the microscope: Can the bacteria be matched to the original culture?

Got Yogurt?