Humans possess an excellent natural defense system to fight against undesirable microorganisms. When these microorganisms get inside the body, a whole series of cells and messages come into play to coordinate the efforts to eliminate the intruders. This army that protects us is called the immune system. Combat units of the immune system

Think of your immune system as an army made up of the following six combat units: 1) Macrophages

Target: anything they find in their path.

Role: to ingest harmful microorganisms; to activate helper T lymphocytes (TH1 and TH2) 2) B lymphocytes

Target: microorganisms and infected cells

Role: to secrete antibodies that attach to microorganisms or cells thereby helping to destroy them 3) Cytotoxic T lymphocytes

Target: infected cell

Role: to kill infected cells 4) NK cells (natural killer)

Target: infected cells

Role: to kill cells that appear to be abnormal 5) T helper type 1 lymphocytes (TH1)

Character: Captain of the cytotoxic T lymphocytes (bearing a small crest of a marksman on their sweaters)

Ro Read More

Humans possess an excellent natural defense system to fight against undesirable microorganisms. When these microorganisms get inside the body, a whole series of cells and messages come into play to coordinate the efforts to eliminate the intruders. This army that protects us is called the immune system.

Combat units of the immune system

Think of your immune system as an army made up of the following six combat units:

1) Macrophages

Target: anything they find in their path.

Role: to ingest harmful microorganisms; to activate helper T lymphocytes (TH1 and TH2)

2) B lymphocytes

Target: microorganisms and infected cells

Role: to secrete antibodies that attach to microorganisms or cells thereby helping to destroy them

3) Cytotoxic T lymphocytes

Target: infected cell

Role: to kill infected cells

4) NK cells (natural killer)

Target: infected cells

Role: to kill cells that appear to be abnormal

5) T helper type 1 lymphocytes (TH1)

Character: Captain of the cytotoxic T lymphocytes (bearing a small crest of a marksman on their sweaters)

Role: to activate cytotoxic T lymphocytes

6) T helper type 2 lymphocytes (TH2)

Character: Captain of the B lymphocytes (bearing a small crest of Robin Hood on their sweaters)

Role: to activate B lymphocytes

Recognizing the intruder

Each T and B lymphocyte has been trained intensively to recognize molecules that belong to its own organism (the self). Therefore, when it sees a molecule that it does not know (the non-self), it automatically knows that it’s an intruder and sounds the alarm.

Macrophages are able to rid the body of a great number of microorganisms – those whose surfaces contain molecules that the macrophages can bind to. Macrophages are particularly attracted to infected cells and microorganisms covered in antibodies. The collaboration between macrophages and the antibody-producing B lymphocytes increases the effectiveness of the fight against the intruder.

In the case of NK cells, the situation is slightly different since they do not recognize the intruder but rather the effect of the intruder. If the cell appears abnormal, it’s probably because it contains an intruder…This diseased cell must thus be killed before it allows any new intruders to escape!


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

Our defenses against germs: the immune system

Armand-Frappier Museum

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


Vaccines

Do you know why you can only catch chicken pox once in your lifetime? Actually, it is possible for the chicken pox virus to re-infect a person who has already had the disease…But his immune system will recognize and eliminate the virus so rapidly that the symptoms of the disease will never be felt. Vaccine production uses this principle to our advantage.

The goal of a vaccine is to show our body what the harmful microorganism looks like without, however, giving it the disease. To do this, we inject a healthy person with living weakened microorganisms, dead microorganisms, microorganisms that resemble the harmful microorganism, or fragments of microorganisms. The body will recognize the strange molecules and will eliminate them without getting infected. A very important step in this elimination is the production of memory cells that will remember the intrusive molecules. Later, if the real microorganism appears, the body will recognize it immediately thanks to these memory cells. This is how the body avoids disease!

Vaccines may be used against all types of harmful microorganisms, including vir Read More
Vaccines

Do you know why you can only catch chicken pox once in your lifetime? Actually, it is possible for the chicken pox virus to re-infect a person who has already had the disease…But his immune system will recognize and eliminate the virus so rapidly that the symptoms of the disease will never be felt. Vaccine production uses this principle to our advantage.

The goal of a vaccine is to show our body what the harmful microorganism looks like without, however, giving it the disease. To do this, we inject a healthy person with living weakened microorganisms, dead microorganisms, microorganisms that resemble the harmful microorganism, or fragments of microorganisms. The body will recognize the strange molecules and will eliminate them without getting infected. A very important step in this elimination is the production of memory cells that will remember the intrusive molecules. Later, if the real microorganism appears, the body will recognize it immediately thanks to these memory cells. This is how the body avoids disease!

Vaccines may be used against all types of harmful microorganisms, including viruses and bacteria. Some examples are the influenza vaccine (caused by the influenza virus), the one against hepatitis B (also caused by a virus) or the one against meningococcus (caused by a bacteria responsible for meningitis).

Antibiotics

Antibiotics are molecules produced by microorganisms to defend themselves against other microorganisms. We have simply used these antibiotics to increase our protection against microbes. It should be specified that antibiotics are only effective against bacteria (such as the bacteria that cause tuberculosis, salmonellosis and pneumonia). Viruses are not at all affected by antibiotics. There are, however, some anti-viral agents that can be used to treat viral infections such as those caused by the herpes or HIV viruses. Moreover, antifungal and antipaludism treatments are available to fight diseases caused respectively by fungi or parasites such as those that causes malaria.

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

Vaccination

Photo : Barbara Bélanger

© Barbara Bélanger, Armand-Frappier Museum


Antibiotic treatment on bacteria

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


For centuries, man has been fighting problems of food preservation.

Some pathogenic microorganisms can develop in food and be subsequently ingested by humans. To avoid consumption of spoiled food, numerous techniques have been developed to preserve the freshness of food longer and ensure a better control of its quality.

Food preservation methods, old and current, were established according to one or several of the following principles: Prevent contamination Inhibit microbial growth and metabolism (microbiostatic activity) Kill the microorganisms (microbiocide activity)

Here are seven preservation techniques that rely on one or the other of these principles. Aseptic manipulation and treatment High temperatures Low temperatures Read More

For centuries, man has been fighting problems of food preservation.

Some pathogenic microorganisms can develop in food and be subsequently ingested by humans. To avoid consumption of spoiled food, numerous techniques have been developed to preserve the freshness of food longer and ensure a better control of its quality.

Food preservation methods, old and current, were established according to one or several of the following principles:

  • Prevent contamination
  • Inhibit microbial growth and metabolism (microbiostatic activity)
  • Kill the microorganisms (microbiocide activity)

Here are seven preservation techniques that rely on one or the other of these principles.

  1. Aseptic manipulation and treatment
  2. High temperatures
  3. Low temperatures
  4. Dehydration
  5. High osmotic pressure
  6. Chemical additives
  7. Irradiation

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

The various stages of food processing and packaging are potential sources of contamination. Some foods can be sterilized, put into sterile containers, and sealed under aseptic conditions. These products can then be stored at room temperature.
The various stages of food processing and packaging are potential sources of contamination. Some foods can be sterilized, put into sterile containers, and sealed under aseptic conditions. These products can then be stored at room temperature.

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

Canning
At the beginning of the 19th century, the Frenchman Nicolas Appert invented canning, also called appertisation, a preservation method that is still one of the most widely used today. Stored at room temperature, the contents of the can are stable for at least a year. The food is placed in the containers, which are sealed and immersed in boiling water (100 to 120°C). This process does not guarantee a sterile product but it kills the anaerobic bacteria Clostridium botulinum capable of forming spores that produce a deadly toxin.
Pasteurization
Pasteurization, invented in the 19th century by Louis Pasteur, was first used to ensure that milk could be consumed safely. It is still used today for the preservation of other beverages and foods. The process involves heating the product continuously at 62.8°C for 30 minutes or 71.1°C for 15 seconds, then cooling it rapidly. This time-temperature relationship was determined to kill the bacteria Mycobacterium tuberculosis (which causes tuberculosis) et Coxiella burnetii (which causes Q fever), two pathogenic microorganisms Read More
  • Canning
At the beginning of the 19th century, the Frenchman Nicolas Appert invented canning, also called appertisation, a preservation method that is still one of the most widely used today. Stored at room temperature, the contents of the can are stable for at least a year. The food is placed in the containers, which are sealed and immersed in boiling water (100 to 120°C). This process does not guarantee a sterile product but it kills the anaerobic bacteria Clostridium botulinum capable of forming spores that produce a deadly toxin.
  • Pasteurization
Pasteurization, invented in the 19th century by Louis Pasteur, was first used to ensure that milk could be consumed safely. It is still used today for the preservation of other beverages and foods. The process involves heating the product continuously at 62.8°C for 30 minutes or 71.1°C for 15 seconds, then cooling it rapidly. This time-temperature relationship was determined to kill the bacteria Mycobacterium tuberculosis (which causes tuberculosis) et Coxiella burnetii (which causes Q fever), two pathogenic microorganisms that can be found in milk.
  • Sterilization
The milk is sterilized by being kept at an extremely high temperature of 148.9°C for 1 or 2 seconds. The milk does not develop a “cooked” flavor, its nutritional quality is preserved, it requires no refrigeration, and can be stored indefinitely.

3. Low temperatures

Refrigerating or freezing food, even if the temperature is extremely cold, cannot kill microorganisms. Temperatures approaching 0°C and lower delay the growth and the metabolism of microorganisms. In fact, prepared frozen food (a temperature of -32°C is used to avoid the formation of ice crystals) is increasingly popular. However, as soon as the food is defrosted, the microorganisms start to grow again, which is why it is highly recommended to never refreeze food which has been previously frozen and then thawed out.


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

Refrigerating or freezing food, even if the temperature is extremely cold, cannot kill microorganisms. Temperatures approaching 0°C and lower delay the growth and the metabolism of microorganisms. In fact, prepared frozen food (a temperature of -32°C is used to avoid the formation of ice crystals) is increasingly popular. However, as soon as the food is defrosted, the microorganisms start to grow again, which is why it is highly recommended to never refreeze food which has been previously frozen and then thawed out.
Refrigerating or freezing food, even if the temperature is extremely cold, cannot kill microorganisms. Temperatures approaching 0°C and lower delay the growth and the metabolism of microorganisms. In fact, prepared frozen food (a temperature of -32°C is used to avoid the formation of ice crystals) is increasingly popular. However, as soon as the food is defrosted, the microorganisms start to grow again, which is why it is highly recommended to never refreeze food which has been previously frozen and then thawed out.

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

Hot
Applying heat to food evaporates the water it contains; this inhibits the growth of microorganisms but does not, however, kill them. Cold
The food is first frozen, then a powerful vacuum is applied so that the ice is converted directly to water vapor. This leaves the food and the microorganisms dehydrated. Contrary to dehydration using heat, this process does not alter the shape or the properties of the food that can thus be reconstituted.

  • Hot
Applying heat to food evaporates the water it contains; this inhibits the growth of microorganisms but does not, however, kill them.
  • Cold
The food is first frozen, then a powerful vacuum is applied so that the ice is converted directly to water vapor. This leaves the food and the microorganisms dehydrated. Contrary to dehydration using heat, this process does not alter the shape or the properties of the food that can thus be reconstituted.

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

Addition of sugar
Water is removed from microbial cells when they are placed in solutions containing large quantities of sugar. This inhibits the microorganisms’ growth but does not kill them. Yeasts and fungi are more resistant than bacteria to high osmotic pressure. This is why it is more common to see jellies and jams contaminated with microscopic fungi rather than bacteria after being exposed to air. Condensed milk is also preserved due to high concentrations of lactose and sucrose, which also remove water from microbial cells. Addition of salt
Water is also removed from microbial cells when they are placed in solutions containing large quantities of salt. The salting of food, in addition to improving its flavor, prevents the microorganisms from reproducing.
  • Addition of sugar
Water is removed from microbial cells when they are placed in solutions containing large quantities of sugar. This inhibits the microorganisms’ growth but does not kill them. Yeasts and fungi are more resistant than bacteria to high osmotic pressure. This is why it is more common to see jellies and jams contaminated with microscopic fungi rather than bacteria after being exposed to air. Condensed milk is also preserved due to high concentrations of lactose and sucrose, which also remove water from microbial cells.
  • Addition of salt
Water is also removed from microbial cells when they are placed in solutions containing large quantities of salt. The salting of food, in addition to improving its flavor, prevents the microorganisms from reproducing.

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

Addition of organic acids
Only a few organic acids are legally accepted as food preservatives. Sorbic and propionic acids are used to inhibit the growth of fungi in bread. Nitrites and nitrates
Nitrites and nitrates are added to meat to preserve their color and inhibit the growth of anaerobic bacteria. This practice is considered controversial because of the possible role of nitrates and nitrites as mutagenic or carcinogenic agents. Substances produced during manufacturing
In some cases, chemical preservatives are produced during the manufacturing of the product or during the preservation process. Sauerkraut and pickles, which are prepared by fermentation, are thus preserved by acetic (vinegar), lactic, and propionic acids produced by the fermentiscible microorganisms. Smoking food generates antibacterial compounds that penetrate and preserve the meat.

  • Addition of organic acids
Only a few organic acids are legally accepted as food preservatives. Sorbic and propionic acids are used to inhibit the growth of fungi in bread.
  • Nitrites and nitrates
Nitrites and nitrates are added to meat to preserve their color and inhibit the growth of anaerobic bacteria. This practice is considered controversial because of the possible role of nitrates and nitrites as mutagenic or carcinogenic agents.
  • Substances produced during manufacturing
In some cases, chemical preservatives are produced during the manufacturing of the product or during the preservation process. Sauerkraut and pickles, which are prepared by fermentation, are thus preserved by acetic (vinegar), lactic, and propionic acids produced by the fermentiscible microorganisms. Smoking food generates antibacterial compounds that penetrate and preserve the meat.

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

Food that is "radiating freshness"


Irradiation is a relatively new method of food preservation. It consists of exposing the food to the direct action of electromagnetic radiation, which increases its shelf life. The irradiation lasts only the time it takes to expose the food to the rays and it does not render the products radioactive. This preservation process is gaining in popularity because it could help us with one of our greatest global challenges, i.e., to feed a world population that is constantly growing. By adequate food preservation, we could effectively reduce the loss of perishables, as well as lower the incidence of serious diseases caused by microorganisms such as toxoplasmosis, salmonellosis, listeriosis, chlolera, etc. Nonionizing
Nonionizing radiation uses ultraviolet rays. If the exposure time and the intensity are sufficient, the microorganisms present in the food product exposed to the UV will be killed. However, this type of radiation has a limited power of penetration and it thus only used for controlling surface microorganisms, such as in bakeries or meat processing rooms, for example. Read More

Food that is "radiating freshness"


Irradiation is a relatively new method of food preservation. It consists of exposing the food to the direct action of electromagnetic radiation, which increases its shelf life. The irradiation lasts only the time it takes to expose the food to the rays and it does not render the products radioactive. This preservation process is gaining in popularity because it could help us with one of our greatest global challenges, i.e., to feed a world population that is constantly growing. By adequate food preservation, we could effectively reduce the loss of perishables, as well as lower the incidence of serious diseases caused by microorganisms such as toxoplasmosis, salmonellosis, listeriosis, chlolera, etc.

  • Nonionizing
Nonionizing radiation uses ultraviolet rays. If the exposure time and the intensity are sufficient, the microorganisms present in the food product exposed to the UV will be killed. However, this type of radiation has a limited power of penetration and it thus only used for controlling surface microorganisms, such as in bakeries or meat processing rooms, for example.
  • Ionizing
Ionizing radiation can use Cobalt-60, a source of gamma rays, which are similar in nature to light but at much higher energy levels. The rays destroy some bonds in the DNA of the microorganisms, which can no longer reproduce and then die.

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

Marinade

Photo : Nicole Catellier

© Nicole Catellier, Cinémanima 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 .

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