Microorganism: Treponema pallidum is the bacterium responsible for syphilis.

Disease: syphilis

Occurrence of the disease

History: many hypotheses have been proposed to account for the origin of syphilis in Europe. Some authors mention that Christopher Columbus and his crew may have contracted syphilis during their voyage to the West Indies (1492). Others think that syphilis existed many centuries ago in Africa and that it appeared in Europe during the population migrations (1500). During the 16th century, the Italian physician Franscatoro wrote a poem in which he described syphilis "seeds" transmissible by sexual contact. During the 18th century, the term "venereal" was attributed to sexually transmissible diseases, referring to the Roman goddess of love, Venus.

Current situation: fewer than 50 cases of syphilis were reported in Quebec in 1998.

Mechanism of action of the microorganism: the microorganism enters the body through the mucous membranes or scratches on the skin. It then travels Read More

Microorganism: Treponema pallidum is the bacterium responsible for syphilis.

Disease: syphilis

Occurrence of the disease

History: many hypotheses have been proposed to account for the origin of syphilis in Europe. Some authors mention that Christopher Columbus and his crew may have contracted syphilis during their voyage to the West Indies (1492). Others think that syphilis existed many centuries ago in Africa and that it appeared in Europe during the population migrations (1500). During the 16th century, the Italian physician Franscatoro wrote a poem in which he described syphilis "seeds" transmissible by sexual contact. During the 18th century, the term "venereal" was attributed to sexually transmissible diseases, referring to the Roman goddess of love, Venus.

Current situation: fewer than 50 cases of syphilis were reported in Quebec in 1998.

Mechanism of action of the microorganism: the microorganism enters the body through the mucous membranes or scratches on the skin. It then travels to lymph nodes of the infected region and spreads throughout the body.

Symptoms of the disease: rash, hair loss, discomfort, and fever. In untreated cases, syphilis can attack the heart, nerves, eyes, and liver. Mental retardation, blindness, an unsteady gait, and dementia have also been observed. Many of these symptoms have been associated with famous people such as Al Capone and Adolf Hitler.

Incubation period: an average of three weeks

Contagious period: the contagious period is associated with the presence of lesions. The disease is rarely transmitted after the first year of infection.

Hosts: humans

Transmission: syphilis is a contagious disease that can be contracted by sexual contact; it can also be transmitted from an infected mother to her child.

Treatment: antibiotics such as penicillin

Geographical distribution of the microorganism: worldwide

Prevention: use of a condom

Vaccine: not available


© Armand-Frappier Museum, 2008. All rights reserved.

Treponema pallidum

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


Microorganism: the bacterium Clostridium tetani

Disease: tetanus

Occurrence of the disease

Current situation: a hundred cases of tetanus are reported each year in the United States. The majority of reported cases occur among intravenous drug users. In Canada there were two cases of tetanus reported in Ontario in 1998.

Prevention: control measures are difficult to implement as the bacteria are widely present in soil.

Mechanism of action of the microorganism: when the bacteria die they produce a toxic substance (neurotoxin) which damages the cells of the nervous system of the infected individual.

Symptoms of the disease: cramps and muscle contractions around a wound and stiffness in the jaw muscles are the first symptoms. At a more advanced stage the disease causes contractions of the facial muscles, which develops into an inability to open the mouth. The later symptoms include contraction of the muscles from the heel to the back resulting in a curvature of the body. Death may result fr Read More

Microorganism: the bacterium Clostridium tetani

Disease: tetanus

Occurrence of the disease

Current situation: a hundred cases of tetanus are reported each year in the United States. The majority of reported cases occur among intravenous drug users. In Canada there were two cases of tetanus reported in Ontario in 1998.

Prevention: control measures are difficult to implement as the bacteria are widely present in soil.

Mechanism of action of the microorganism: when the bacteria die they produce a toxic substance (neurotoxin) which damages the cells of the nervous system of the infected individual.

Symptoms of the disease: cramps and muscle contractions around a wound and stiffness in the jaw muscles are the first symptoms. At a more advanced stage the disease causes contractions of the facial muscles, which develops into an inability to open the mouth. The later symptoms include contraction of the muscles from the heel to the back resulting in a curvature of the body. Death may result from involuntary contractions of the respiratory muscles.

Incubation period: normally three to 21 days but may start in as little as one day and last for several months.

Contagious period: this disease is not transmissible from one human to another.

Hosts: the intestine of several animal species.

Transmission: the bacteria may only enter an organism by means of open wounds. The death rate varies between 30% and 90%.

Discoverer of the microorganism: Nicolaier (1885)

Treatment: treatment for this disease is not particularly effective, which is why vaccination against tetanus is so important. If you are injured and you feel a stiffness in the muscles surrounding the wound, it is important to disinfect the area immediately, obtain a booster shot of the vaccine, and begin a course of penicillin. Immediate treatment is crucial.

Geographical distribution of the microorganism: this bacterium can be found in hospitals, in the soil, in dust, and in the excrement of humans and farm animals.

Prevention: The tetanus vaccine is combined with other vaccines. The T of DPT represents the vaccine against tetanus. Several injections and booster shots are required because the immune system forgets the information obtained from previous inoculations (DPT-Polio-Hib at 2, 4, 6 and 18 months, vaccine DPT-Polio at 4 and 6 years and d2T5 at 14 to 16 years and at 10-year intervals for adults).

Vaccine: the vaccine consists of the inactivated toxin produced by the bacterium. Following the injection of the six recommended doses, the tetanus vaccine is approximately 90% effective.

Side effects of the vaccine: in 60% of cases the child feels a little discomfort or pain at the site of the injection and in 50% of cases fever may appear within 48 hours of the injection.


© Armand-Frappier Museum, 2008. All rights reserved.

Clostridium tetani

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


Microorganism: the bacterium Mycobacterium tuberculosis

Disease: tuberculosis

Occurrence of the disease

History: Tuberculosis is a very old disease. In fact, lesions caused by tuberculosis have been found on human skeletons dating from 3000 BC. Until the 1800s, people believed that tuberculosis was a divine punishment. In Europe, between 1780 and 1831, large migrations of rural populations into the cities caused a major increase in the incidence of tuberculosis. At that time, one death in seven was caused by tuberculosis. Deplorable sanitation, malnutrition, and child labor were also factors favoring the spread of the disease. In 1878, the bacteriologist Robert Koch discovered the bacterium responsible for tuberculosis; he received the Nobel Prize for this work. In 1924, Calmette and Guérin produced BCG, the first vaccine against this terrible disease.

Current situation: Large-scale vaccination against tuberculosis has not been done in Quebec since 1975, since the incidence of the disease is low. However, although the incidenc Read More

Microorganism: the bacterium Mycobacterium tuberculosis

Disease: tuberculosis

Occurrence of the disease

History: Tuberculosis is a very old disease. In fact, lesions caused by tuberculosis have been found on human skeletons dating from 3000 BC. Until the 1800s, people believed that tuberculosis was a divine punishment. In Europe, between 1780 and 1831, large migrations of rural populations into the cities caused a major increase in the incidence of tuberculosis. At that time, one death in seven was caused by tuberculosis. Deplorable sanitation, malnutrition, and child labor were also factors favoring the spread of the disease. In 1878, the bacteriologist Robert Koch discovered the bacterium responsible for tuberculosis; he received the Nobel Prize for this work. In 1924, Calmette and Guérin produced BCG, the first vaccine against this terrible disease.

Current situation: Large-scale vaccination against tuberculosis has not been done in Quebec since 1975, since the incidence of the disease is low. However, although the incidence of the disease was very low during the 1970s, there were 1,798 cases reported in Canada during 1998. Worldwide, the number of cases of tuberculosis reported has grown throughout the 1980s to reach eight million persons per year; three million of these will die.

Forecast: we must watch this disease very carefully; if not controlled, it could once again cause major devastation.

Mechanism of action of the microorganism: bacteria enter a person’s body when she or he breathes contaminated air. Once in the lungs, the bacteria multiply, which causes an immune reaction. If the cells of the immune system are incapable of eliminating the bacteria, there will be formation of tubercles. These tubercles in the lungs are very dangerous, as they can liquefy and create holes, or harden and form masses.

The bacterium responsible for tuberculosis can also cause foci of infection at other places in the body, causing “miliary tuberculosis.” Tuberculosis can also evolve into meningitis or into scrofula (infection of the lymph nodes).

Symptoms of the disease: cough, weight loss, spitting up of blood

Incubation period: two to six weeks

Contagious period: the contagious period lasts as long as bacteria are present in the lungs.

Hosts: humans and, occasionally, other mammals

Transmission: tuberculosis spreads in the same way as influenza, that is, through droplets containing microorganisms that are present in the air when an infected person coughs.

Discoverer of the microorganism: Robert Koch in 1882.

Treatment: certain antimicrobial drugs such as isoniazid and pyrazinamide. It is also possible to use the antibiotic streptomycin if the bacteria are resistant to isoniazid.

Geographical distribution of the microorganism: worldwide; however, industrialized countries are much less affected by this disease than are developing countries.

Prevention: isolation of patients so that they do not infect others, as well as regular hand washing. There is also a vaccine that can be administered as prevention.

Vaccine: BCG (Bacille Calmette-Guérin) is a live vaccine with limited effectiveness. It is made from a bacterium similar to that which causes tuberculosis, but which normally infects cattle.


© Armand-Frappier Museum, 2008. All rights reserved.

Mycobacterium tuberculosis

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


Microorganism: the bacterium Salmonella typhi

Disease: typhoid fever

Occurrence of the disease

History: "Typhoid Mary": Between 1896 and 1906, a cook infected with typhoid fever unknowingly infected 28 individuals while preparing their meals. Mary Mallon was a healthy carrier of the disease. In other words, she had no symptoms but could nevertheless transmit the disease. Mary had worked as a cook for seven different families in the New York area. When the 28 cases of typhoid fever were reported from these seven families, Mary was arrested by the Health Department of New York City. She was brought to a hospital where physicians examined her feces and found them to contain the typhoid bacteria. Mary was released but was prohibited from cooking for any other families. However, Mary changed her name and began to work again as a cook. During a period of five years she infected many other victims and was arrested a second time. The police kept her in a secure place until her death in 1938.

Current situation: currently, 17 million Read More

Microorganism: the bacterium Salmonella typhi

Disease: typhoid fever

Occurrence of the disease

History: "Typhoid Mary": Between 1896 and 1906, a cook infected with typhoid fever unknowingly infected 28 individuals while preparing their meals. Mary Mallon was a healthy carrier of the disease. In other words, she had no symptoms but could nevertheless transmit the disease. Mary had worked as a cook for seven different families in the New York area. When the 28 cases of typhoid fever were reported from these seven families, Mary was arrested by the Health Department of New York City. She was brought to a hospital where physicians examined her feces and found them to contain the typhoid bacteria. Mary was released but was prohibited from cooking for any other families. However, Mary changed her name and began to work again as a cook. During a period of five years she infected many other victims and was arrested a second time. The police kept her in a secure place until her death in 1938.

Current situation: currently, 17 million cases including 600,000 deaths are reported each year around the world. In the United States, 2,484 cases were reported in 1950 compared to fewer than 500 today. Most cases are from southeast Asia and northeast Africa. In Canada, 82 cases of typhoid fever were reported in 1998.

Mechanism of action of the microorganism: bacteria are taken in by mouth and travel to the intestine. The microorganisms infiltrate the cells lining the intestine and eventually end up in the blood and the liver.

Symptoms of the disease: as suggested by its name, typhoid fever causes fever but it also cause severe headache, abdominal pain, and weight loss.

Incubation period: from three days to a month

Contagious period: the contagious period lasts as long as there are bacteria in the feces, which usually corresponds to the period between a week after the infection begins until recovery (approximately three months after the onset of the infection). However, two to five per cent of infected individuals become chronic carriers.

Hosts: humans and less often domestic animals

Geographical distribution of the microorganism : many African and Asian countries as well as Central and South America

Transmission: spread is mostly through contaminated water. The bacteria are present in the feces of infected individuals until three months after the infection. Moreover, two to five per cent of infected individuals become healthy carriers, which means that they can transmit the disease during their entire life through their feces. These individuals have no symptoms.

Discoverer of the microorganism: Eberth in 1880

Treatment: typhoid fever bacteria are becoming more and more resistant to drugs. However, a drug called ciprofloxacin is still effective.

Prevention: recommended preventive measures include pasteurizing milk, purifying water, isolation of infected individuals, and prohibiting infected individuals from handling food. Regular hand washing and disposal of human feces in sanitary containers protected from flies are also effective prevention measures. In fact, flies can transmit the disease because they often land on human feces.

Vaccine: there are two types of vaccines against typhoid fever. One of them is live and attenuated; it is administered orally and requires a booster seven years later. The other is inactivated and a booster is required after three years.

Vaccination is recommended but not required.


© Armand-Frappier Museum, 2008. All rights reserved.

Salmonella typhi

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


Microorganism: the bacterium Rickettsia prowazekii

Disease: typhus

Occurrence of the disease

History: in 1906, Howard T. Ricketts discovered the bacteria responsible for typhus, which was transmitted by lice. While pursuing his work in the laboratory, and despite his careful technique, he was bitten while transferring some lice. In 1910, Ricketts died of typhus and the bacterium he studied was named Rickettsia in his honor.

Mechanism of action of the microorganism: as soon as the Rickettsia get into the bloodstream, they infect the cells of the blood vessels.

Symptoms of the disease: headaches, fever, muscle aches, and skin rashes.

Incubation period: one to two weeks, typically 12 days

Contagious period: transmission from humans to lice can occur between two to three days after the fever has diminished. The lice invariably die in the two weeks following the infection but their feces are only contagious between two and six days following ingestion of infec Read More

Microorganism: the bacterium Rickettsia prowazekii

Disease: typhus

Occurrence of the disease

History: in 1906, Howard T. Ricketts discovered the bacteria responsible for typhus, which was transmitted by lice. While pursuing his work in the laboratory, and despite his careful technique, he was bitten while transferring some lice. In 1910, Ricketts died of typhus and the bacterium he studied was named Rickettsia in his honor.

Mechanism of action of the microorganism: as soon as the Rickettsia get into the bloodstream, they infect the cells of the blood vessels.

Symptoms of the disease: headaches, fever, muscle aches, and skin rashes.

Incubation period: one to two weeks, typically 12 days

Contagious period: transmission from humans to lice can occur between two to three days after the fever has diminished. The lice invariably die in the two weeks following the infection but their feces are only contagious between two and six days following ingestion of infected blood.

Hosts: humans, lice, and possibly squirrels

Transmission: the disease is transmitted through the bite of a rickettsia-infected louse. The bacteria contained in the contaminated feces of the louse enter the bloodstream at the site of the bite or of the injury caused when the person scratches himself. An infected person can then infect new lice, which can then continue to transmit the disease.

Treatment: antibiotics such as doxycycline, tetracycline, or chloramphenicol

Geographical distribution of the microorganism: louse-infected places, typically in certain mountainous regions of Mexico, Central and South America, central and east Africa, and in several Asian countries.

Prevention: reducing louse infestations with insecticides and minimizing contacts with infected people.

Vaccine: not available


© Armand-Frappier Museum, 2008. All rights reserved.

Transmission of typhus

Illustration by Bruno Laporte

© Illustration by Bruno Laporte


Microorganism: the bacterium Bordetella pertussis.

Disease: whooping cough (also known as "pertussis").

Occurrence of the disease

Current situation: every year, approximately 100,000 people die from whooping cough around the world. In 1998, 4,850 cases of whooping cough were reported in Quebec, and 8,797 cases in Canada. In the United States, fewer than ten deaths are reported every year.

Mechanism of action of the microorganism: the bacteria enter the body through the respiratory tract, and attach themselves to the cells lining the lungs, where they produce toxic substances known as toxins. These toxins are responsible for the effects of the disease.

Symptoms of the disease: the initial symptoms resemble those of a cold, but a prolonged and persistent cough develops subsequently. Later effects include pneumonia, convulsions, and serious neurological complications.

Incubation period: seven to 14 days.

Contagious period: approximately three weeks fro Read More

Microorganism: the bacterium Bordetella pertussis.

Disease: whooping cough (also known as "pertussis").

Occurrence of the disease

Current situation: every year, approximately 100,000 people die from whooping cough around the world. In 1998, 4,850 cases of whooping cough were reported in Quebec, and 8,797 cases in Canada. In the United States, fewer than ten deaths are reported every year.

Mechanism of action of the microorganism: the bacteria enter the body through the respiratory tract, and attach themselves to the cells lining the lungs, where they produce toxic substances known as toxins. These toxins are responsible for the effects of the disease.

Symptoms of the disease: the initial symptoms resemble those of a cold, but a prolonged and persistent cough develops subsequently. Later effects include pneumonia, convulsions, and serious neurological complications.

Incubation period: seven to 14 days.

Contagious period: approximately three weeks from the onset of cough. Antibiotic therapy can reduce the contagious period to approximately five days from the onset of treatment.

Hosts: humans are probably the only hosts.

Transmission: inhalation of airborne bacteria in saliva droplets produced by infected individuals.

Discoverers of the microorganism: Bordet and Gengou in 1906.

Treatment of the disease: antibiotics such as erythromycin, tetracycline, and chloramphenicol.

Geographical distribution of the microorganism: worldwide. Over the last four decades, there has been a marked decline in the incidence of whooping cough in countries, such as Canada, that have instituted immunization programs.

Prevention: the DTP-Polio-Hib vaccine at two, four, six, and 18 months and the DTP-Polio vaccine at four and six years. These vaccines contain a diphtheria vaccine combined with other vaccines (the "P" in the name of the vaccine stands for "pertussis"). Several booster injections are necessary.

Vaccine: the vaccine contains dead whooping cough bacteria (Bordetella pertussis). After the five recommended boosters have been administered, the vaccine is effective in 85% of cases.

Side effects of the vaccine: sixty per cent of children experience some pain at the site of injection, and 50% experience fever within 48 hours of the injection. The incidence of side effects has dropped considerably since the introduction of an acellular vaccine in 1998.


© Armand-Frappier Museum, 2008. All rights reserved.

Whooping cough

Illustration by Bruno Laporte

© Illustration Bruno Laporte


Learning Objectives

The learner will:
  • familiarize himself with the vocabulary used in microbiology;
  • explain the relationship between developments in imaging technology and the current understanding of the cell;
  • identify which microorganisms are infectious, how the immune system fights against them, and the reinforcements of modern medicine;
  • describe the benefits of microorganisms.

Teachers' Centre Home Page | Find Learning Resources & Lesson Plans