The Causes of Disease: Bacteriology

Dr. P. Warren

Professor, Faculty of Medicine, University of Manitoba

By the mid-nineteenth century, diseased organs could be detected. The identification of the patterns and natural history of various diseases was leading to their being distinguished and identified. That many diseases occurred within families produced the theory that many were the result of an inherited weakness often enhanced by habit. For instance tuberculosis was thought to be the result of too much study in a 'sickly' individual. Other diseases, such as smallpox, were thought to be the result of contagion while others, such as rheumatism, were due to miasmas. The agents responsible for disease awaited clarification. In fact major advances in combating disease had occurred through careful observation and experimentation with no understanding of the underlying pathogenesis of the disease.

The Conquest of Smallpox


Smallpox is one of the most feared diseases we have known- it was distinguished from other diseases with rashes by the Islamic Rhazes. It was a devastating infection - for instance smallpox killed half the Hurons in Canada in the seventeenth century; in eighteenth century Britain, one in four died; and more recently the Icelandic immigrants to Gimli.

It was well known that one only got smallpox once. In the Islamic world, it became the habit to "engraft" people with the dried pustule from smallpox and that this provided protection. In 1718, Lady Mary Montague (1689-1762), wife of the British ambassador to Constantinople and an early leader of feminism, learnt of this practice, called variolation or inoculation, and introduced it to Britain after first having her own children treated.

In 1721, the British Royal Family wished to have their children protected. Was variolation safe? After consulting the Solicitor General the King decided to test it on prisoners first. On August 29, 1721 three male and two female prisoners were inoculated - all developed mild smallpox and recovered. All were pardoned.

It was safe - but was it effective? One of the women was made to share a bed with a ten-year-old boy with smallpox and she survived with no ill effects thus confirming protection. Queen Caroline then had it tested on orphans and again it was safe. At last the Royal children were inoculated. However inoculation never became common for too often a full-blown case of smallpox was produced.

Edward Jenner (1749-1823), a family physician who had been encouraged by John Hunter (1729-83), the great anatomist, in his studies of natural history discovered the safe prevention of smallpox. "But why think? Why not try the experiment" wrote Hunter to Jenner. Jenner was great naturalist and became a fellow of the Royal Society for his work on the nesting behaviour of the cuckoo. Jenner learnt from a dairymaid that she could not catch smallpox because she had had cowpox. This was well known locally. Jenner realized that if true this phenomenon could be used to replace variolation. He inoculated 8 year old James Phipps with cowpox from Sarah Nelmes. Six weeks later he inoculated James with smallpox. No illness developed. Vaccination as his practice was called spread around the world. It was brought to Newfoundland by John Clinch who had corresponded with Jenner in 1796 and was using it the next year.

Jenner's original report of his observation was rejected for publication by the Royal Society as incomplete- he had too few subjects for the result to be certain. But in 1798 he published his fuller studies An inquiry into the causes and Effects of the Variola Vaccinae and the procedure caught on- in 1802 the Government rewarded him with 10,000 pounds. Jenner became famous. The vaccine was carried hard to maintain on long voyages and so it was often transferred on humans. For instance the Spanish shipped it around the world to their colonies on the arms of a succession of orphans. The Hudson's Bay Company vaccinated the aboriginal people- though whether for humanity or simply to preserve the source of their wealth is debated. But some people feared vaccination, and from time to time serious reactions occur to it such as encephalitis. And anti-vaccination movements have continued. Nonetheless vaccination succeeded and in 1989 the WHO declared that smallpox was eradicated from the world.

The Origin of Bacteriology


The discoveries that led to an understanding of most of the diseases the world faced were the culmination of the work of Louis Pasteur (1822-95) who was chemist. His first work was on tartaric acid which founded the science of stereochemistry. His ability was recognized and at age 24 he was awarded a professorship at Lille where fermentation industries were common. Pasteur applied his chemical knowledge to studies of wine, beer and vinegar. He concluded that fermentation was produced by living organisms, not pure chemical reactions.

He showed that the living organisms are carried in the air and that putrefaction and infections had much in common with fermentation. By now microscopes had reasonable resolution. Bacteria had been observed in diseased bodies. Did bacteria arise from spontaneous generation or from without? Pasteur studied these questions by aspirating air through cotton and found that bacteria were caught in the cotton- if the cotton was placed in broth it caused fermentation but if heated first nothing occurred. Such studies led him to consider disease and in 1878 he argued the germ theory of infection to the French Academy of Medicine.



An example of the unraveling of infectious disease is the research on Anthrax that was feared as a major killer of cattle on farms and a considerable hazard to humans. One mystery was that the disease could strike a herd of cattle suddenly out of the blue. In 1849 Pollender (1800-79) had found bacilli in the blood of dead cattle and in 1868 Davaine (1812-82) showed that injection of 1 millionth of a drop of that blood caused anthrax in a cow. The mysteries of anthrax intrigued a family physician, Robert Koch (1843-1910) in Eastern Germany. In 1876 Robert Koch set out to prove that the Anthrax bacilli caused the disease. He studied the blood of local animals that died of anthrax. He produced cultures of the organism. At the same time he had noticed that an old boiled potato was spotted with blobs of different colour and reasoned that each was a colony of a single organism. He realized that cultures could be used to isolate organisms. Koch went on to show with his cultures that anthrax could form spores that were extremely hardy but with appropriate heat (30ยบ C) and oxygen they became active and could infect. The spores could survive for decades in the soil, a particular risk being the burial of its victims in the pasture. Year's later cows grazing on these fields would disturb the anthrax and become infected. Koch presented his studies in 1876 and was rewarded with appointment as a professor to the Institute of Infectious Disease in Berlin.

Parallel with Koch, Pasteur worked with anthrax and performed repetitive diluted cultures of anthrax 1877. He found that this attenuated the bacilli reducing its virulence. Remembering the work on preventing smallpox he used this attenuated strain for immunization. His critics scoffed that this would work. In 1881 Pasteur proved his point in a public exhibit at Pouilly le Fort. He inoculated 24 sheep, 1 goat and 6 cows with the attenuated anthrax and then challenged them and an equal number of controls with virulent bacilli. All immunized animals lived. 21 control sheep, 2 before the eyes of the spectators, and 4 of the cows died. Pasteur triumphed and when he presented the results proposed the name for this protection should be vaccine and vaccination in honour of Jenner's work. Anthrax is viewed as a hazard to be used in germ warfare- it was feared that Saddam Hussein would use it in the Gulf War and Canadian troops were immunized against it. The Sergeant Kipling court-martial for refusal to be immunized is one consequence of this practice.

The Golden Age of Bacteriology


Koch and his assistants used the new technology such as the Zeiss condenser that improved the resolution of the microscope and the dyes of the German chemical industry that gave them stains to find bacteria. As Koch said it was "a period where the gold lay all on the surface: all one had to do was pick it up". Koch identified the organisms for cholera, trypanosomias, and his colleagues Gaffky typhoid and Loeffler diphtheria. Koch moved for his cultures from the potato slices with which his work began to liquid gelatin and then to the agar plates used today and named after his technician Petri.


At this time tuberculosis was the major lethal disease facing Europe - it was debated still if it was hereditary or a contagion. Koch focussed his research onto it. He used various stains and eventually with Methylene blue and Bismarck brown he stained and so identified tubercle bacilli in the tubercles of dead consumptives and then of animals. Culture on his usual media did not succeed. Eventually he mimicked nature - he used blood serum jellied with his wife's agar that she used for jam making and incubated these in test tubes at the body temperature of a guinea pig. He was patient for it was some weeks before the tubes were speckled with colonies. Each colony was pure bacilli. He inoculated many animals- rabbits, mice, guinea pigs, ducks, cats, monkeys- even turtles, eels, frogs and goldfish. The latter lived on, the former mammals succumbed to TB and were riddled with bacilli. Fresh cultures were prepared as before.

These experimental steps that were used to prove that a bacterium cause a disease became known as Koch's Postulates.

Koch's Postulates

1. The given organisms must be found regularly in the diseased tissue of the infected person or animal.

2. The organisms must be capable of being grown in pure culture.

3. The pure culture must produce the disease when administered to the experimental animal.

4. The organism must be found in the experimentally produced diseases and be capable of being recovered again in pure culture.

On March 24, 1882, Robert Koch presented his discovery of the Tubercle bacillus and the proof that it caused tuberculosis. Paul Ehrlich said "that evening was engraved on my memory as the most majestic scientific event that I have ever participated in". On the 10th April he published his discovery and the news of this great discovery swept the world.

On April 22, Tyndall announced the discovery to the English speaking world and on the 3rd May this was reproduced in the New York Times.

The Tuberculin Scandal

In 1890 Koch announced that he had arrested the growth of Mycobacterium tuberculosis with an agent that he called tuberculin: "my experiments with these substances, though lasting more than a year, are not yet concluded, so that all I can say at present is that if guinea pigs are treated they cannot be inoculated with tuberculosis, and guinea pigs which already are in the late stages of the disease are completely cured".

Dazzling publicity and awards followed. Despite Germany's laws on secret remedies Koch did not reveal the nature of tuberculin. There are suspicions that Koch, embroiled in a divorce, had been paid handsomely by a drug company or that the German government, for excessive national pride, forbade him to give the secret. Thousands flocked to Berlin and were treated with tuberculin with no controls- experience showed soon that tuberculin was useless or even dangerous. In 1891 Koch announced that tuberculin was simply a glycerin extract of tubercle bacilli.

It was noted that at the site of injection considerable reactions developed. In due course this phenomenon became the skin test for tuberculosis by von Pirquet (1874-1929) in 1907- also called the Mantoux test.


But some diseases that were thought to be infectious remained mysterious. One was rheumatic fever. In 1882 a surgeon Ogston (1844-1929) found straight lines of cocci and clumps of cocci in skin abscesses and named the former streptococci. In 1887 Klein (1844-1925-) isolated Streptococci from the blood of patients with Scarlet Fever. In 1924 George and Gladys Dick (1881-) identified Strep in the throats of Scarlet Fever patients. Streptococcus was often found in the throat of those who went on the develop rheumatic fever. But despite huge efforts Streptococci could not be found in the blood, joints or heart of those with rheumatic fever. Eventually in 1934 it was determined that rheumatic fever was the consequence of the body's immune reaction to the Streptococcus. An example that immunity to an organism may protect as with vaccination or harm. Incidentally, Dr. F.T. Cadham of Winnipeg was the first to describe an allergic reaction to a microorganism with asthma to molds in 1924.