Introduction to MicroB

Medical/Clinical Microbiology

The study of the aetiology of infections, characteristics of pathogens, mode of spread, pathogenesis, laboratory diagnosis, antimicrobial treatment, control/prevention of infection, and immune response to infection.

Branches of Microbiology

The four main branches are Bacteriology, Parasitology, Virology, and Mycology.

Endogenous Infection

An infection caused by microorganisms that are already part of the host’s own normal flora (microbiota) when they invade a site where they are not usually found or when host immunity is compromised.

Exogenous Infection

An infection caused by pathogens acquired from an external source outside the host’s body (e.g., from the environment, another person, or an animal).

Zacharias Jansen

A Dutch spectacle maker credited with the first fabrication of the microscope.

Marcello Malpighi (1628–1694)

Italian scientist and first to extensively examine biological materials with a microscope

Robert Hooke (1665)

Examined cork under a microscope and observed that plant materials are composed of small compartments he called “cells.”

Anton van Leeuwenhoek (1632–1723)

Dutch scientist who assembled hundreds of microscopes (some magnifying 270x) and first described bacteria and protozoa

Spontaneous Generation

The disproven belief, introduced by Aristotle (~350 BC), that living organisms could arise from nonliving matter (e.g., mice from dirty hay, maggots from meat).

Francesco Redi (1626–1697)

First to formally challenge spontaneous generation

Lazzaro Spallanzani (1729–1799)

Repeated Needham’s broth experiments with sealed flasks

Rudolf Virchow (1858) – Biogenesis

Introduced the concept of biogenesis: living cells can only arise from pre-existing living cells

Louis Pasteur – Swan-Neck Flask Experiment

Placed nutrient broths in long-necked bent flasks

Pasteur’s Three Key Discoveries

(1) Microorganisms can be present in nonliving matter

Germ Theory of Disease

The theory, arising from Pasteur’s work, that microorganisms are responsible for causing the physical and chemical changes that lead to infectious disease.

John Snow (1813–1858)

Physician who mapped cholera cases during a London epidemic and traced them to a contaminated water pump

Miasma Theory

The disproven belief that disease was caused by “bad air” from decaying matter

Joseph Lister

Applied the germ theory to surgery in the 1860s

Semmelweis (1840)

Demonstrated that physicians transmitting puerperal (childbed) fever from patient to patient could be stopped by disinfecting their hands between patients.

Florence Nightingale (1820–1910)

English nurse who pioneered cleanliness and antiseptic techniques in nursing

Robert Koch

First scientist to establish the actual cause of a disease

Koch’s Postulate 1

The same pathogen must be present in every case of the disease.

Koch’s Postulate 2

The pathogen must be isolated from the diseased host and grown in pure culture.

Koch’s Postulate 3

The pathogen from the pure culture must cause the disease when inoculated into a healthy susceptible host.

Koch’s Postulate 4

The pathogen must be re-isolated from the inoculated animal and shown to be identical to the original pathogen.

Limitations of Koch’s Postulates

Do not apply to organisms found in both sick and healthy people (e.g., Vibrio cholerae)

Edward Jenner (1749–1823)

English physician who developed the first vaccine by inoculating humans with cowpox material to prevent smallpox

Vaccination / Immunity

The process (named after vacca = cow, in honour of Jenner’s work) of inoculating with attenuated or killed microorganisms to produce immunity

Pasteur’s Attenuated Vaccines

Pasteur discovered that neglected (aged) cultures of fowl cholera were weakened (attenuated) but still made chickens immune

Discovery of Penicillin – Alexander Fleming (1881–1955)

Scottish biologist who observed that Penicillium notatum mould destroyed Staphylococcus colonies on contaminated plates