Microorganism: generally caused by the bacillus Clostridium perfringens

Disease: gangrene

Occurrence of the disease

History: gangrene is a common battlefield disease, since it is associated with wound infections.

Current situation: gangrene is relatively rare in industrialized countries.

Mechanism of action of the microorganism: the microorganism enters the host through wounded tissue. The bacteria produce a poisonous toxin that destroys affected tissue. The bacterium responsible for gangrene is anaerobic, that is, it can grow only in the absence of oxygen. In untreated cases, the mortality rate is from 40 to 60%.

Symptoms of the disease: severe pain in infected areas, caused by death of muscle tissue; edema (accumulation of fluid in tissues); and discharge.

Incubation period: less than three days

Contagious period: person-to-person transmission has never been observed.

Hosts: most humans have this type of bac Read More

Microorganism: generally caused by the bacillus Clostridium perfringens

Disease: gangrene

Occurrence of the disease

History: gangrene is a common battlefield disease, since it is associated with wound infections.

Current situation: gangrene is relatively rare in industrialized countries.

Mechanism of action of the microorganism: the microorganism enters the host through wounded tissue. The bacteria produce a poisonous toxin that destroys affected tissue. The bacterium responsible for gangrene is anaerobic, that is, it can grow only in the absence of oxygen. In untreated cases, the mortality rate is from 40 to 60%.

Symptoms of the disease: severe pain in infected areas, caused by death of muscle tissue; edema (accumulation of fluid in tissues); and discharge.

Incubation period: less than three days

Contagious period: person-to-person transmission has never been observed.

Hosts: most humans have this type of bacteria in their large intestines. Furthermore, this organism is found in soil around the world.

Transmission: contamination of a wound by gangrene bacteria, from the soil or from the large intestine.

Discoverer of the microorganism: Welch and Nuttall in 1892.

Treatment: administration of antitoxin and antibiotics such as penicillin and tetracycline. The use of oxygen can also prevent the growth of the bacteria, since this species cannot tolerate oxygen. Amputation of affected limbs is often necessary in order to prevent the spread of the disease throughout the body.

Geographical distribution of the microorganism: worldwide

Prevention: ensure cleanliness of wounds following surgery.

Vaccine: not available


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

Clostridium perfringens

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


Microorganism: the bacillus Clostridium botulinum, serotypes A and G.

Disease: botulism (food poisoning)

Occurrence of the disease

Current situation: in 1999, fewer than 15 cases were reported in Canada.

Mechanism of action of the microorganism: C. botulinum is capable of forming spores, which are a very resistant form of the bacterium. When the bacteria or the spores enter the body, often through contaminated food or through a wound a toxin (a poison) produced by the bacteria proceeds to the nervous system, where it blocks a specific molecule known as acetylcholine. This molecule is responsible for the transmission of messages between nerve cells. In blocking acetylcholine, the disease interferes with the transmission of messages in the nervous system, which eventually will cause paralysis.

Symptoms of the disease: disturbed vision, difficulty in swallowing and speaking, muscular weakness, nausea, and vomiting.

Incubation period: 12 to 36 hours

Contagiou Read More

Microorganism: the bacillus Clostridium botulinum, serotypes A and G.

Disease: botulism (food poisoning)

Occurrence of the disease

Current situation: in 1999, fewer than 15 cases were reported in Canada.

Mechanism of action of the microorganism: C. botulinum is capable of forming spores, which are a very resistant form of the bacterium. When the bacteria or the spores enter the body, often through contaminated food or through a wound a toxin (a poison) produced by the bacteria proceeds to the nervous system, where it blocks a specific molecule known as acetylcholine. This molecule is responsible for the transmission of messages between nerve cells. In blocking acetylcholine, the disease interferes with the transmission of messages in the nervous system, which eventually will cause paralysis.

Symptoms of the disease: disturbed vision, difficulty in swallowing and speaking, muscular weakness, nausea, and vomiting.

Incubation period: 12 to 36 hours

Contagious period: the disease is generally not spread from person to person.

Hosts: spores of the bacterium C. botulinum are found in soil around the world.

Transmission: infection generally occurs when food is not heated sufficiently during the canning process to kill the spores of C. botulinum.

Discoverer of the microorganism: Van Ermengem in 1896.

Treatment: intravenous antitoxin administered as quickly as possible.

Geographical distribution of the microorganism: worldwide

Prevention: strict adherence to safety regulations in the food industry, and education of the public concerning safe methods of home canning. Honey should not be given to infants before one year of age. Avoid using the contents of cans that appear swollen, or that have a bad odor. A person who suspects that he or she has eaten contaminated food should go immediately to a hospital for stomach pumping.

Vaccine: not available.


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

Clostridium botulinum

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


Microorganism: the bacterium Bacillus anthracis

Disease: anthrax, or charbon

Occurrence of the disease

History: anthrax has a very interesting history. In the past, this disease was often associated with people who worked with sheep’s wool. Around 1850, more careful research enabled John Bell, an English doctor, to identify the bacterial origin of the disease. The bacterium responsible, Bacillus anthracis, was isolated for the first time by Robert Koch in 1876. In 1881, three researchers including Louis Pasteur demonstrated the possibility of immunization against anthrax using weakened cultures of the bacterium.

Current situation: this disease is most widespread in tropical countries, among persons who work with livestock. Fewer than ten cases per year are reported in the United States.

Mechanism of action of the microorganism: the bacteria can infect the skin, the lungs, and even the intestines. The symptoms of the disease are caused by an exotoxin produced by the bacteria that poisons surro Read More

Microorganism: the bacterium Bacillus anthracis

Disease: anthrax, or charbon

Occurrence of the disease

History: anthrax has a very interesting history. In the past, this disease was often associated with people who worked with sheep’s wool. Around 1850, more careful research enabled John Bell, an English doctor, to identify the bacterial origin of the disease. The bacterium responsible, Bacillus anthracis, was isolated for the first time by Robert Koch in 1876. In 1881, three researchers including Louis Pasteur demonstrated the possibility of immunization against anthrax using weakened cultures of the bacterium.

Current situation: this disease is most widespread in tropical countries, among persons who work with livestock. Fewer than ten cases per year are reported in the United States.

Mechanism of action of the microorganism: the bacteria can infect the skin, the lungs, and even the intestines. The symptoms of the disease are caused by an exotoxin produced by the bacteria that poisons surrounding tissue.

Anthrax bacteria have a very resistant form known as spores; this enables them to remain alive for many decades in soil or animal products.

Symptoms of the disease: the disease usually develops in a cut or scratch on the skin, which blackens as the infection develops. Symptoms appear such as headache, fever, and nausea. Death occurs in 20% of untreated cases. Pulmonary anthrax can also occur, following inhalation of the anthrax bacterium. Symptoms of pulmonary anthrax are fever and anaphylactic shock; death occurs within 48 hours. If the bacteria are swallowed, nausea and vomiting cause death in 60% of cases.

Incubation period: usually between one and seven days.

Contagious period: person-to-person transmission is very rare. However, soil contaminated with spores of the bacterium can remain infectious for decades.

Hosts: infected animals. Carcasses of infected animals can end up in the soil, thereby shedding anthrax bacteria. This is why B. anthracis can be found in soil in many parts of the world. The bacterium can also be found in products derived from animal carcasses.

Transmission: transmission to humans can occur through direct contact or through an intermediary made from infected animals, such as sheep’s wool. Anthrax can also be spread through soil contaminated by infected animals, or through plant fertilizers that contain the bones of infected animals.

Discoverer of the microorganism: Koch in 1876.

Treatment: some antibiotics such as penicillin G in combination with streptomycin.

Geographical distribution of the microorganism: generally speaking, anthrax is rare in industrialized countries. Regions where the bacterium is considered endemic are found in South and Central America, eastern and southern Europe, in Asia, and in Africa.

Prevention: vaccination of livestock and of workers at risk, such as members of the armed forces.

Vaccine: acellular vaccine. This vaccine does not contain complete bacteria, but antigenic components of the bacterium.


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

Bacillus anthracis

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


Microorganism: the bacterium Yersinia pestis

Disease: plague

Occurrence of the disease

History: during the Middle Ages, this disease was known as the Black Death, because of the black stains it produced in the skin.

Current situation: in the United States, this disease is rare (around 25 cases per year) and the mortality rate is 15%. Canada has not had a single case of plague for many years.

Mechanism of action of the microorganism: the bacteria multiply in the blood and block the natural defenses of the infected person.

Symptoms of the disease: the first symptoms of plague are non-specific. These include fever, muscle aches, chills, nausea, sore throat, and headache. As the disease progresses, there is swelling of the lymph nodes. These swellings are known as buboes. Subcutaneous hemorrhages appear, causing black patches on the skin. Untreated plague is fatal in 50 to 60% of cases, within three to five days. In some cases the microorganisms may invade the lungs.

Incu Read More

Microorganism: the bacterium Yersinia pestis

Disease: plague

Occurrence of the disease

History: during the Middle Ages, this disease was known as the Black Death, because of the black stains it produced in the skin.

Current situation: in the United States, this disease is rare (around 25 cases per year) and the mortality rate is 15%. Canada has not had a single case of plague for many years.

Mechanism of action of the microorganism: the bacteria multiply in the blood and block the natural defenses of the infected person.

Symptoms of the disease: the first symptoms of plague are non-specific. These include fever, muscle aches, chills, nausea, sore throat, and headache. As the disease progresses, there is swelling of the lymph nodes. These swellings are known as buboes. Subcutaneous hemorrhages appear, causing black patches on the skin. Untreated plague is fatal in 50 to 60% of cases, within three to five days. In some cases the microorganisms may invade the lungs.

Incubation period: from one to seven days

Contagious period: under appropriate conditions, fleas can transmit the disease over the course of months.

Transmission: this disease is spread by rodents and their fleas; the fleas can spread the disease to other animals, including humans. The microorganism is actually transmitted through the bite of an infected flea.

Hosts: wild rodents such as squirrels. Domestic cats may sometimes be a source of infection.

Discoverer of the microorganism: Kitasato and Yersin in 1894

Treatment: certain antibiotics such as streptomycin or tetracycline

Geographical distribution of the microorganism: most mountainous and rural high-altitude regions of Africa, Asia, and South America.

Prevention: vaccine

Vaccine: there is a vaccine made from killed bacteria; it is administered in three doses.

In regions where the disease is endemic, vaccination may be recommended if direct contact with rodents might occur.


© Dennis Kunkel Microscopy, Inc.

Yersinia pestis

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


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.

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