Microbiology

Microbiology

You don’t have to be a microbiologist or scientist to work in a kitchen or restaurant, but basic knowledge of microbiology will help you to understand why there are regulations for handling food. Microbes are so tiny that they can only be seen with a microscope. They are everywhere: on our bodies, on animals, in water, soil and air. Fortunately, 99% of all microbes are harmless or even beneficial. However, one percent of microbes can cause severe illness and death. We will concentrate on the disease-causing microbes that can be carried by food.

In this module, we will explore two topics:

  • Microbes
  • Bacterial microbes

Learning Objectives

When you have completed this module, you will be able to:

  • Recognize the 4 types of microbes and their role in food contamination.
  • Identify the role of spore-forming-bacteria in causing food poisoning.
  • Recognize common disease-causing bacteria, the conditions in which they multiply and how they can be a danger to the food service industry.

Self Test

Use the Self Test to discover what you already know about the topics covered in this module. That way, you can focus on the topics you are not familiar with.

If you do not feel ready for the Self Test yet, move on to the rest of the module. You may return any time by clicking on the Menu at the top of this page.

Microbes

Microbiology is the study of very small (microscopic) living organisms known as microbes or micro-organisms. These organisms are so tiny that they can only be seen with a microscope.

There are almost as many myths and misconceptions about microbiology as there are micro-organisms! The following exercise, Germ Conquest, will provide an overview of the topics covered in this module.

Germ Conquest

Question: All microbes cause disease.

99% of all microbes are harmless to us or are beneficial to us.

Not all microbes cause disease. 99% of all bacteria are harmless to us or are beneficial to us.

Question: Bacteria need water and sunlight to reproduce.

While bacteria do need water to reproduce, they do not need sunlight.

Bacteria do need water to multiple but they do not need sunlight.

Question: Bacteria reproduce most rapidly between 4 – 60°C (40 – 140°F).

Bacteria reproduce most rapidly between these temperatures. This temperature range is called the Temperature Danger Zone.

Bacteria reproduce most rapidly between these temperatures. This temperature range is called the Temperature Danger Zone.

Question: Insects play no part in transmitting microbes.

Many insects can transmit microbes that cause diseases to people and animals; examples are Lyme Disease from ticks and Malaria from mosquitoes.

Many insects can transmit microbes that cause diseases to people and animals; examples are Lyme Disease from ticks and Malaria from mosquitoes.

Question: The Hepatitis virus can be spread by food.

One type of Hepatitis virus that causes food poisoning can be spread to people from uncooked foods.

One type of Hepatitis virus that causes food poisoning can be spread to people from uncooked foods.

Germ Conquest

Question: Under ideal conditions, bacteria can multiply to more than one million in a 24-hour period.

If bacteria have everything they need to multiply they can grow very quickly.

If bacteria have everything they need to multiply they can grow very quickly.

Question: Sanitizing kills all microbes.

Sanitizing kills most microbes. When you sanitize dishes, you reduce the number of bacteria and spores to a safe level which will not cause people to become ill. The only way to make things completely microbe-free (germ-free) is to sterilize; sterilizing can only be done with special equipment found in hospitals and dental offices.

Sanitizing kills most microbes. When you sanitize dishes, you reduce the number of bacteria and spores to a safe level which will not cause people to become ill. The only way to make things completely microbe-free (germ-free) is to sterilize; sterilizing can only be done with special equipment found in hospitals and dental offices.

Question: Lemon makes food more acidic.

Lemon is acidic and can make food it is added to more acidic.

Lemon is acidic and can make food it is added to more acidic.

Question: Gravy should be slowly reheated in the steam table.

Gravy should be reheated quickly using a stove. Steam tables are not designed for reheating food; they are designed to keep hot food at a high enough temperature that micro-organisms cannot grow.

Gravy should be reheated quickly using a stove. Steam tables are not designed for reheating food; they are designed to keep hot food at a high enough temperature that micro-organisms cannot grow.

Question: A pathogen is a disease-causing microbe.

Microbes that can cause diseases are called “pathogens”.

Microbes that can cause diseases are called “pathogens”.

Microbes - Types

The different types of microbes include: bacteria, viruses, fungi, parasites and protozoa.

Bacteria

Bacteria are very small, single-celled organisms that can only be seen with a microscope . There are thousands of species, which can be found in just about every material and environment. Most bacteria are harmless. E. coli O157:H7 is an example of a strain of bacteria that can make you sick.

Fungi

Fungi are living organisms that are neither animals nor plants and include moulds and yeasts. Aspergillus mould is an example of a harmful fungus. It produces toxins that can cause cancer. This mould can be found in nuts, grains, and the milk of cows that were fed mouldy grains.

Parasites & Protozoa

Parasites live on or in humans and use them to grow. People can get them from contaminated water, eating undercooked meat from a contaminated animal or cross-contamination.

Trichinosis is a type of parasitic infection that can spread through raw or undercooked pork or wild game.

Protozoa are a type of parasite. They live in the digestive tract of people and animals and can cause foodborne illness. They get into food from contaminated water. Giardiasis, also known as Beaver Fever, and cryptosporidiosis are examples of foodborne illness called by protozoa.

Viruses

Viruses are smaller than bacteria and cannot live on their own. Viruses need a host to survive. They get inside the cells of the host and take it over. Hepatitis A is a virus that can spread to humans through contaminated food and water and make them sick.

Microbes - How Microbes Travel

All four types of microbes are found throughout our environment in soil, dust, water or air. They are also in and on humans, animals, birds, fish and insects.

Microbes cannot walk, crawl or fly. They get from place to place when someone or something moves them. You could say they are experts in hitchhiking; they move from place to place by attaching themselves to people, insects, and rodents. Microbes are dropped off as people, insects and rodents touch other surfaces and food. Microbes can also end up in the air and move around in the wind.

Let’s look more closely at one of those “rides”!

Microbes - How Microbes Travel

Flies don’t look harmful, do they? Well, in fact they are worse than cockroaches for the ease with which they can carry microbes. Think about where flies hang out. They are often found on dead animals, feces, and garbage. Microbes attach themselves to the tiny hairs on the fly’s body and mouth parts and are carried to wherever the fly lands.

This is something to keep in mind the next time you see a fly. You never know where it was hanging out before it landed on your food!

Did you know?

Flies cannot eat solid food, so to soften it up, they vomit on it. Then they stomp the vomit in until the food turns into a liquid, usually stomping in a few microbes for good measure. Then, when their food is good and runny, they suck it in, probably dropping some excrement at the same time. When they have finished eating, it’s your turn.

Microbes - Beneficial Microbes

Not all microbes are harmful. In fact, 99% of all microbes are harmless and may even be beneficial. Can you think of any examples of products or processes in which microbes play an important or beneficial role?

There are 7 examples on the next screen. Try to come up with at least two, before you look.

Microbes - Beneficial Microbes

You know now that there are many more good microbes than bad. Here are some examples of processes in which microbes play a beneficial role:

  • Bread making – Bread dough rises with the help of yeast.
  • Wine making – Bacteria are used to ferment the grape juices into wine.
  • Cheese making – Bacteria are used to ferment the milk. Some cheeses (like blue cheese) have moulds in them.
  • Dairy industry – Bacteria are found in yogurt and sour cream.
  • Medicines – Penicillin is made from mould.
  • Digestion – Bacteria in our intestines help us digest food.
  • Breaking down waste – Bacteria break down waste in septic tanks.

So who are the bad guys?

Microbes - Pathogens

The 1% of microbes that can make us sick are called pathogens. There are some bacteria, some viruses and some fungi that can cause disease.

Most people don’t know the term “pathogens” and refer to them as “germs“. Pathogens are germs that cause illness in people. We’ll try to use the term “pathogen”.

Pathogens are found on the skin and in the fecessaliva, urine, blood and other body fluids of people or animals, and also in the environment.

Did you know?

Mould is similar to a tiny plant, with root-like and stem-like structures, and a flower-like top. As mould grows and matures, it sheds spores (like the seeds of a dandelion flower), which are dispersed into the air until they land on something that they can grow in.

As moulds grow, they produce poisons (toxins) that can make people sick if they eat them. This is why you must discard any food that has signs of mould growth.

Microbes - Pathogens

There are many bacterial pathogens that cause foodborne illness. The following chart lists some examples:

Bacteria Source Interesting to know
Salmonella (2000 species) Poultry and raw eggs You will learn more about it in the Foodborne Illness Module.
E. coli 0157:H7 “hamburger disease” Cattle intestines Can cause bloody diarrhea and kidney failure.
Staphylococcus aureus Found on the human body: noses, infected cuts/eyes and pimples Forms a toxin in food that can’t be destroyed by cooking. See the Foodborne Illness Module.
Clostridium perfringens Soil Found on vegetables, cereals, raw meats, and poultry.
Bacillus cereus Soil Found in rice, vegetables, cooked meat and custards. This is a spore-forming bacteria.
Campylobacter jejuni Poultry and cattle intestines Prevention: proper cooking, cleaning and handwashing.
Vibrio parahaemolyticus Grows in silt (soil) in coastal waters where raw fish and shellfish are harvested. It is not recommended to eat raw seafood.
Listeria monocytogenes Luncheon meats (cold cuts), soft cheese Grows well at refrigeration temperatures; can cause miscarriage in pregnant women.

What does that mean to you as an employee in the food industry or in your home?

Microbes - Pathogens

As a food handler, your hands come into contact with raw and cooked foods. That means you risk contaminating the food of others. You can help to reduce the spread of pathogens by washing your hands frequently and ensuring you have no open cuts or wounds that may jeopardize the safety of the food you serve.

Remember: Pathogens cannot be detected in food by smell or taste. Reduce the risk of pathogens in the food by following the safe food handling principles and practices you will learn in this course.

The next few screens will give you a chance to practice what you have learned about pathogens.

Microbes - Exercises

Not all of the following statements about viruses are correct.

Select the TRUE statements about viruses:

Microbes - Exercises

Select the TRUE statements about fungi:

Remember! It is important to discard any food showing signs of mold and yeast growth.

Microbes - Exercises

Select the TRUE statements about bacteria:

Microbes - Exercises

Select the TRUE statements about parasites, including protozoa:

Bacterial Microbes

We’ll begin this section by looking at bacteria in more detail.

Under the right conditions, bacteria divide in 2 every 20 minutes. One bacterium can turn into billions within a 24-hour time period.

What conditions do bacteria need in order to grow?

Bacterial Microbes - FATTOM

There are six factors that affect the growth of bacteria. You can remember the six factors more easily if you remember the first letter of each: FATTOM. Just think of the cartoon of the phantom or think of ‘Fat Tom’, a chef who likes to taste his food!

In the next few slides you will learn about each of the following:

  • Food
  • Acidity
  • Time
  • Temperature
  • Oxygen
  • Moisture

Bacterial Microbes - FATTOM

Food

Bacteria are living organisms that need food. They grow best in food that is moist and high in protein. These foods are considered high-risk foods. Here are some examples:

  • Milk and milk products
  • Sliced melons
  • Garlic-and-oil mixture
  • Poultry: chicken, turkey
  • Meat: beef, pork, lamb and veal
  • Fish and seafood
  • Sprouts
  • Eggs
  • Soy products (like tofu)
  • Cooked rice, beans, grains, vegetables and potatoes
  • Mayonnaise-based salads (like egg, potato and tuna salad)

Bacterial Microbes - FATTOM

Acidity

pH is a measurement of acidity and alkalinity in food. The amount of acidity or alkalinity can be measured with a pH meter. pH scale ranges from 0 to 14.

As you can see from the scale below, foods such as fruit and vinegar are acidic in the 0 to 4.5 range. Although some bacteria can survive in acidic foods, they don’t grow in highly acidic conditions.

Foods such as meat, dairy and even melons are considered to be weakly acidic or neutral, in the 4.5 to 7 range. This is the type of environment bacteria grow very well in.

Foods such as egg whites and soda crackers are alkaline, in the range from 8 to 14. These alkaline foods will not support the growth of bacteria.

Bacterial Microbes - FATTOM

Time

High-risk foods should spend as little time as possible in the Temperature Danger Zone (TDZ); no more than 2 hours. The 2-hour rule gives a good safety margin since you may not know the details of what happened to the food before, during or after the delivery.

Bacterial Microbes - FATTOM

Temperature

 The Temperature Danger Zone (TDZ) is the range from 4°C (40°F) to 60°C (140°F) . Bacteria grow and multiply quickly in food that is kept in the TDZ.

When you handle food, it is important that high-risk foods spend as little time in this temperature range as possible.

High-risk foods should not be in the Temperature Danger Zone (TDZ) for more than 2 hours. The next slide will provide more information on the TDZ.

Keeping food in the refrigerator keeps it out of the TDZ, but this only slows down bacterial growth. Bacteria do not stop growing in the fridge!

Holding food above 60°C (140°F) will stop bacteria from growing and will even kill some.

High cooking temperatures will kill bacteria.

Bacterial Microbes - FATTOM

Oxygen

Some bacteria will only grow where there is oxygen present. They are called aerobic bacteria.

Other bacteria will only grow where there is no oxygen present and are called anaerobic bacteria.

Foodborne illness can be caused by either type; aerobic or anaerobic.

Bacterial Microbes - FATTOM

Moisture

Water activity is a way of measuring the amount of moisture in a food.

Bacteria need water to grow. They will survive in foods that do not have a lot of moisture, but will not grow.

For example, salmonella bacteria survive on an eggshell but they don’t multiply there because of lack of moisture.

Bacterial Microbes - Exercises

Now that you know what bacteria need to multiply, see if you can figure out which of the foods in the following screens have the greatest risk of bacterial growth.

In order to control bacteria in foods, it is important to understand the conditions that bacteria need to grow and multiply. The following exercise demonstrates these conditions. On each page, you will find 2 images of food with a description.

Select which of the two foods has the greatest risk of bacterial growth.

Hard Cheese

Sorry.

A hard cheese like Parmesan is safer than soft cheese like Ricotta, because there is less moisture available for bacteria to grow.

Soft Cheese

Correct!

Soft cheese like Ricotta is more dangerous than hard cheese like Parmesan because there is more moisture available for bacteria to grow.

Bacterial Microbes - Exercises

Select which type of food has the greatest risk of bacterial growth.

Chicken

Correct!

Poultry is more dangerous because it is high in protein and moisture. Chocolate cake is safer because most chocolate cakes don’t have a high protein or moisture content.

Chocolate Cake

Sorry.

Chocolate cake is safer because most chocolate cakes don’t have a high protein or moisture content. Poultry is more dangerous because it is high in protein and moisture.

Bacterial Microbes - Exercises

Select which type of food has the greatest risk of bacterial growth.

Jarred Pickles

Sorry.

Jarred pickles are safer because the pH is too low to support bacterial growth. Whipping cream is more dangerous because of its moisture and protein levels.

Whipping Cream

Correct!

Whipping cream is more dangerous because of its moisture and protein levels. Jarred pickles are safer because the pH is too low to support bacterial growth.

Bacterial Microbes - Exercises

Select which type of food has the greatest risk of bacterial growth.

Homemade garlic in oil

Correct!

Homemade garlic in oil is more dangerous because no oxygen in present around the garlic. This creates a great environment for spore-forming bacteria and can result in botulism. A spray bottle with vegetable oil is safer because it is purchased from a store. Learn more about this in the next section on spore-forming bacteria.

Spray bottle with vegetable oil

Sorry.

A spray bottle with vegetable oil is safer because it is purchased from a store. Homemade garlic in oil is more dangerous because no oxygen in present around the garlic. This creates a great environment for spore-forming bacteria and can result in botulism. Learn more about this in the next section on spore-forming bacteria.

Bacterial Microbes - Exercises

Select which type of food has the greatest risk of bacterial growth.

Bananas

Sorry.

Melons are more dangerous than other fresh fruit because bacteria, such as Salmonella, have been found on the outer skin. When the melon is sliced, the bacteria are dragged to the inside by the knife and are able to survive in the fruit because it is not acidic like most other fruits are. Bacteria do not normally live or grow in acidic environments.

Melons

Correct!

Melons are more dangerous than other fresh fruit. Pathogens such as Salmonella have been found on the outside surface of melons. When the melon is sliced, the bacteria are dragged to the inside with the knife. The flash of melons, unlike other fruits, is not acidic, so pathogens are able to live and grow.

Bacterial Microbes - Exercises

Select which type of food has the greatest risk of bacterial growth.

Cooked Meatballs (Holding temp; 60°C (140°F)

Sorry.

Cooked meatballs kept at an internal temperature of 60°C (140°F) are safer than raw ground beef, because bacteria cannot grow above 60°C. Raw meat may naturally contain bacteria; this is why proper cooking is important. Refrigeration temperatures of 4°C (40°F) only slow the growth of those bacteria. Raw ground beef has everything else bacteria need to grow, like neutral pH, protein and moisture.

Raw Ground Beef (Fridge temp; 4°C (40°F)

Correct!

Ground beef stored in a fridge is more dangerous than cooked meatballs held at 60°C. Raw meat may naturally contain bacteria; this is why proper cooking is important. Refrigeration temperatures of 4°C (40°F) only slow the growth of those bacteria. Raw ground beef has everything else bacteria need to grow, like neutral pH, protein and moisture. Cooked meatballs kept at an internal temperature of 60°C (140°F) are safer than raw ground beef, because bacteria cannot grow above 60°C.

Bacterial Microbes - Spore-forming bacteria


Some bacteria, called spore-forming bacteria, are able to protect themselves from unfavourable conditions by forming a heavy protective layer or coat. Once they are in this protective state, they are called ‘spores‘.

Examples of unfavourable conditions are:

  • Extreme temperature changes (such as freezing and cooking)
  • Dry conditions (such as a lack of water, for example in dry foods such as uncooked rice)
  • Acidic conditions (for example, when food becomes acidic by adding lemon or vinegar, as in a salad dressing)
  • Lack of food
  • Cleaning using chemical sanitizers

When conditions are favourable again, the protective coat is removed and the bacteria can begin to grow again.

Spores themselves do not lead to foodborne illness, but the bacteria protected in the spore can.

Bacterial Microbes - Spore-forming bacteria

Where are spores found?

Spores are found everywhere but mostly in soil and dirt. They get into our food when they are harvested with vegetables, spices and grains. They can also get onto our meat and poultry.

All spore-forming bacteria can only grow in food with very little oxygen.

Which kinds of foods provide the best conditions for spore-forming bacteria to multiply?

Bacterial Microbes - Spore-forming bacteria

Spore-forming bacteria are able to multiply quickly in foods that are:

  • full of protein
  • moist
  • at a pH of 4.5 to 8 (close to neutral)
  • in the temperature danger zone
  • in an absence of oxygen

Examples of spore-forming bacteria are Bacillus cereus and Clostridium botulinum (botulism).

Bacterial Microbes - Spore-forming bacteria

One of the main causes of foodborne illness is spore-forming bacteria. Spores are particularly dangerous to the Food Services Industry because they can survive the cooking temperatures for foods. They can also multiply in improperly cooled or improperly heated foods.

For example, when food takes too long to cool, the temperature drops into the temperature danger zone (TDZ) for much more than 2 hours. This time and temperature combination is ideal for spores to remove their protective layer/protective coat, turn back into bacteria, and multiply.

Most spore-forming bacteria produce a toxin (poison) as they grow. The toxin causes food poisoning.

Try the exercise on the next page, to decide which foods are ideal for the growth of spore-forming bacteria.

Bacterial Microbes - Spore-forming bacteria

Check those items that provide favourable conditions for spore-forming bacteria

Bacterial Microbes - Spore-forming bacteria

A Public Health Inspector says:

Botulism food poisoning is caused by a spore forming bacteria called Clostridium botulinum (C. botulinum). This spore forming bacteria produces the deadliest toxin known to humans. Tiny amounts of the toxin (less than the size of a pin-point) can cause paralysis and death. C. botulinum multiplies in conditions where no oxygen is available. Improperly canned/preserved or vacuum packed food and garlic and oil products provide this condition.

Never use homemade canned goods, garlic and oil products or flavored oils in food service establishments. Always purchase these products from a licensed supplier or manufacturer. The commercial manufacturers have additional preservation methods for reducing the moisture content of foods to prevent botulism spores from turning into active bacteria and producing the deadly toxin.

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