Bacteria

Is this milk still good? Have you ever asked a question like that while in your kitchen? The answer to this and other food safety questions rests in knowing which type of and how much bacteria are present in the foods you eat and on the surfaces in your home. Your challenge is to collect samples of bacteria from a number of food items and surfaces in a virtual kitchen and then determine which type of bacteria are present in each sample. It's time for you to start swabbing.

Planning and Carrying Out Investigations

Bacteria Brochure

What are bacteria?

"Bacteria" is the plural form of the word bacterium. Bacteria are microscopic, single-celled organisms that do not have a nucleus. They also lack other organelles such as mitochondria, the endoplasmic reticulum, and the Golgi apparatus. Bacteria are considered to be microscopic because they cannot be seen without a microscope.

What do bacteria look like?

Bacteria have three main distinct shapes: coccus, bacillus, and spirillum. Coccus bacteria have a spherical shape like a grape, bacillus bacteria are rod-shaped like a tiny little submarine, and spirillum bacteria are spiral-shaped like a spring. Most bacteria live alone, but some are found in clusters.

What is gram staining?

Gram staining is a laboratory technique used to identify bacteria. A stain is applied to a sample of bacteria. Bacteria with a thick cell wall made up of 50 to 90% peptidoglycan stain purple or violet and are called gram positive bacteria. Bacteria with thinner cell walls consisting of only about 10% peptidoglycan are called gram negative, and they stain pink or red.

Are bacteria good or bad?

Most bacteria are beneficial, but some are harmful. Beneficial bacteria are called benign bacteria and harmful bacteria are called pathogens. We need benign bacteria to survive. Without them, we would die. In addition to digesting our food in our intestines, benign bacteria also live on our skin and in our mouths. Benign bacteria are important because they protect us from pathogens that can cause disease or produce poisons called toxins.

Where are bacteria located?

Bacteria are located almost everywhere in nearly every environment, including inside your body, on your skin, in soil, inside and outside of animals, in oceans, deserts, hot springs, snow, and kitchen tables.

How do bacteria reproduce?

Bacteria can reproduce very fast. In fact, some types of bacteria can reproduce as quickly as every twenty minutes. Bacteria reproduce in two ways: asexually and sexually. Asexual reproduction means that there is only one parent and the offspring will be an exact duplicate of the parent. When a bacterium reproduces asexually, it undergoes a process called binary fission, where the parent bacterium splits into two cells. Sexual reproduction involves two parents undergoing a process called conjugation, where the two parents join together and exchange genetic material. Once this happens, the bacteria go through binary fission to produce an offspring with new genetic makeup. Sexual reproduction produces offspring that has traits from both parents.

How do bacteria survive?

Bacteria have to obtain and break down food, and protect themselves from the environment. Some bacteria are autotrophs, which means they use light and chemical energy to synthesize their food. Bacteria that are not autotrophic are called heterotrophs, which means they consume other substances, like other organisms, milk, meat, and decaying material. Bacteria break down food to produce energy in a process called respiration. Most bacteria are aerobic, which means that they need oxygen to survive. However, some bacteria will die if they come in contact with oxygen. These bacteria are called anaerobic bacteria.

Some potential kitchen bacteria

Bacillus cereus B. cereus bacteria are rod-shaped, peritrichous, and gram-positive. These facultative anaerobes can be found in rice and soil. Eating foods contaminated with B. cereus can cause food poisoning. Typical symptoms are diarrhea, abdominal cramps, and vomiting. Campylobacter coli C. coli bacteria are spiral-shaped, gram-negative, and can be either monotrichous or ampitrichous. These microaerophilic bacteria can be found in many mammals and birds. C. coli is a common cause of foodborne disease, such as gastroenteritis. Campylobacter jejuni C. jejuni bacteria are spiral-shaped, gram-negative, and can be either monotrichous or ampitrichous. These microaerophilic bacteria can be found in many mammals and birds. C. jejuni is one of the most common causes of foodborne disease, such as gastroenteritis. C. jejuni infections have also been associated with Guillain-Barre syndrome. Clostridium botulinum C. botulinum bacteria are rod-shaped, peritrichous, and gram-positive. These anaerobes can be found in canned goods, meat products, and seafood. C. botulinum can cause botulism, a rare but serious illness. Escherichia coli E. coli bacteria are rod-shaped, peritrichous, and gram-negative. These facultative anaerobes normally live in the intestines of humans and animals without causing any problems, but certain strains can cause food poisoning. Some of the items that harmful E. coli can be found in are: raw or undercooked meat and seafood, unwashed vegetables, and food handled by people with unclean hands. Helicobacter pylori H. pylori bacteria are spiral-shaped, lopotrichous, and gram-negative. These microaerophilic bacteria only grow in the stomach and are responsible for many cases of ulcers and stomach inflammation. Consuming food or water that has not been cleaned properly can cause H. pylori infections in humans. Lactococcus lactis L. lactis bacteria are sphere-shaped, atrichous, and gram-positive. These facultative anaerobes are non-pathogenic and are widely used in the production of dairy products, like milk and cheese. Wisconsin chose L. lactis as its official state microbe. Legionella pneumophillia L. pneumophillia bacteria are rod-shaped, monotrichous, and gram-negative. These aerobic bacteria can be found in water delivery systems. Breathing in the mist of contaminated water can lead to infection in humans. L. pneumophillia causes most cases of Legionnaires' Disease. Listeria monocytogenes L. monocytogenes bacteria are rod-shaped and gram-positive, and they produce peritrichous flagella at room temperature. These facultative anaerobic bacteria can be found in unpasteurized milk, raw meat, raw seafood, and raw vegetables. L. monocytogenes can cause listeriosis. Salmonella enterica S. enterica bacteria are rod-shaped, peritrichous, and gram-negative. These aerobic bacteria can be found in raw or undercooked eggs, meat, and poultry, and on contaminated surfaces. S. enterica bacteria can cause enteric fever and acute gastroenteritis. Staphylococcus aureus S. aureus are atrichous, gram-positive, sphere-shaped bacteria that form clusters. These facultative anaerobic bacteria normally live on human skin and in nasal passages of healthy humans. However, certain strains can cause skin problems, pneumonia, and food poisoning. Harmful S. aureus bacteria can be found in poultry, eggs, desserts, and on contaminated surfaces. Sponges used to clean surfaces can also become contaminated. S. aureus food poisoning causes a variety of symptoms, such as nausea, vomiting, fever, and diarrhea. Vibrio cholerae V. cholerae bacteria are monotrichous, gram-negative, and have a curved, rod shape. These facultative anaerobic bacteria can be found in seafood, raw vegetables, and contaminated water. V. cholerae can cause cholera in humans. Vibrio vulnificus V. vulnificus bacteria are monotrichous, gram-negative, and have a curved, rod-shaped. These facultative anaerobes can be found in seafood, especially shellfish. Eating food contaminated with V. vulnificus can cause body aches, chills, fever, and blistering skin lesions. Yersinia entercolitica Y. entercolitica bacteria are rod-shaped, peritrichous, and gram-negative. These facultative anaerobic bacteria are commonly found in pigs, and they can also be found in meat, seafood, vegetables, and poultry. Y. entercolitica can cause yersiniosis in humans.