Chapter 1

History and Koch

Four questions asked in order over two centuries: can we see them, where do they come from, do they cause disease, and what do we do about it. Chapter 1 is those four questions and the people who answered them.

Two centuries on one rule

Fig. 1Position is the year of birth; colour is the question each figure was working on. The crowd around 1820–1850 is the germ theory arriving all at once.

Who did what

If a name comes up on the exam, it comes up attached to one specific contribution. Learn the pairing, not the biography.

Seeing them at all

Before anyone could argue about microbes, someone had to see one.

Who	When	Credited with	What they actually did
Robert Hooke	b. 1635	Named the cell	His drawings of cork through a microscope introduced the word "cell" and started cell theory.
Antonie van Leeuwenhoek	b. 1632	First saw living microbes	Ground his own lenses and described the "animalcules" in pond water, saliva and scrapings from his own teeth.

Where do they come from?

A two-century argument, settled by an experiment that let air in but kept dust out.

Who	When	Credited with	What they actually did
Francesco Redi	1626–1697	First challenge to spontaneous generation	Covered jars of meat so flies could not reach them. No maggots appeared, so the maggots came from flies, not the meat.
John Needham	b. 1713	Argued for spontaneous generation	Boiled broth still grew microbes, which he took as proof they arose on their own — his flasks were open to the air.
Lazzaro Spallanzani	b. 1729	Argued against it	Boiled broth in sealed flasks and nothing grew. Critics said he had excluded the "vital force" in air.
Louis Pasteur	b. 1822	Settled the question	His swan-necked flasks let air in but trapped dust in the bend. The broth stayed sterile for months, and grew only when the neck was broken or tipped. Spontaneous generation was wrong.

Do they cause disease?

Establishing that a particular microbe causes a particular disease — not merely that it is present.

Who	When	Credited with	What they actually did
Robert Koch	b. 1843	Linked one microbe to one disease	Found the cause of anthrax and established the etiologic relationship between a microbe and a specific disease. His postulates are the standard for proving causation.

What do we do about it?

The practical consequence: wash, sterilise, vaccinate, and treat.

Who	When	Credited with	What they actually did
Joseph Lister	1827–1912	Antiseptic surgery	Sprayed carbolic acid in the operating theatre and cut surgical deaths sharply.
Ignaz Semmelweis	1818–1865	Handwashing	Showed that doctors washing their hands between the mortuary and the delivery ward stopped childbed fever. He was ignored in his lifetime.
Florence Nightingale	1820–1910	Sanitation and nursing	Used statistics to show that sanitary conditions, not battle wounds, killed most soldiers.
John Snow	1813–1858	Epidemiology	Traced a cholera outbreak to the Broad Street pump and removed its handle — the founding act of epidemiology.
Edward Jenner	1749–1823	Vaccination	Used cowpox material to protect against smallpox, giving us the word vaccine, from vacca, a cow.
Paul Ehrlich	1854–1915	Chemotherapy	Searched for a "magic bullet" that would kill a microbe without harming the patient, and found salvarsan for syphilis.

Koch’s postulates

Four steps, in this order. They prove an etiologic relationship — that one microbe causes one disease, rather than merely turning up alongside it.

1The microorganism must be observed in every case of the disease.
2It must be isolated and grown in pure culture.
3The pure culture, when inoculated into an animal, must reproduce the disease.
4The microorganism must be recovered from the diseased animal.

What they cannot do

Some pathogens cannot be grown in pure culture — viruses, Mycobacterium leprae, Treponema pallidum. Some diseases have no suitable animal model, and for others it would be unethical to infect anyone. The postulates set a standard; they do not always reach it.

Also Koch’s

The postulates get the attention, but the techniques underneath them were his too.

Simple staining techniques
The first photomicrograph of bacteria
The first photomicrograph of bacteria in diseased tissue
Using steam to sterilise media
Using Petri dishes
Techniques for transferring bacteria
The idea of bacteria as distinct species

What counts as alive

Chapter 1 opens with this, and it is worth a mark because growth and reproduction are not the same thing.

Growth

Increase in size

Reproduction

Increase in number

Responsiveness

The ability to respond to changes in the environment

Metabolism

Controlled chemical reactions

Growth is an increase in size; reproduction is an increase in number. A cell forming an endospore is doing neither — one cell becomes one spore, so the population never rises. That distinction turns up on the exam in more than one place.