Science, Tech, Math › Science Bacteria: Friend or Foe? Share Flipboard Email Print These are multiple Helicobacter pylori which are Gram-negative, microaerophilic bacteria found in the stomach. Science Picture Co/Subjects / Getty Images Science Biology Basics Cell Biology Genetics Organisms Anatomy Physiology Botany Ecology Chemistry Physics Geology Astronomy Weather & Climate By Regina Bailey Biology Expert B.A., Biology, Emory University A.S., Nursing, Chattahoochee Technical College Regina Bailey is a board-certified registered nurse, science writer and educator. Her work has been featured in "Kaplan AP Biology" and "The Internet for Cellular and Molecular Biologists." our editorial process Regina Bailey Updated June 24, 2018 Bacteria are all around us and most people only consider these prokaryotic organisms to be disease-causing parasites. While it is true that some bacteria are responsible for a large number of human diseases, others play a vital role in necessary human functions such as digestion. Bacteria also make it possible for certain elements such as carbon, nitrogen, and oxygen to be returned to the atmosphere. These bacteria ensure that the cycle of chemical exchange between organisms and their environment is continuous. Life as we know it would not exist without bacteria to decompose waste and dead organisms, thus playing a key role in the flow of energy in environmental food chains. Are Bacteria Friend or Foe? The decision as to whether bacteria are friend or foe becomes more difficult when both the positive and negative aspects of the relationship between humans and bacteria are considered. There are three types of symbiotic relationships in which humans and bacteria coexist. The types of symbiosis are termed commensalism, mutualism, and parasitism. Symbiotic Relationships Commensalism is a relationship that is beneficial to the bacteria but does not help or harm the host. Most commensal bacteria reside on epithelial surfaces that come in contact with the external environment. They are commonly found on the skin, as well as in the respiratory tract and the gastrointestinal tract. Commensal bacteria acquire nutrients and a place to live and grow from their host. In some instances, commensal bacteria may become pathogenic and cause disease, or they may provide a benefit for the host. In a mutualistic relationship, both the bacteria and the host benefit. For example, there are several kinds of bacteria that live on the skin and inside the mouth, nose, throat, and intestines of humans and animals. These bacteria receive a place to live and feed while keeping other harmful microbes from taking up residence. Bacteria in the digestive system assist in nutrient metabolism, vitamin production, and waste processing. They also aid in the host's immune system response to pathogenic bacteria. Most of the bacteria that reside within humans are either mutual or commensal. A parasitic relationship is one in which the bacteria benefit while the host is harmed. Pathogenic parasites, which cause disease, do so by resisting the host's defenses and growing at the expense of the host. These bacteria produce poisonous substances called endotoxins and exotoxins, which are responsible for the symptoms that occur with an illness. Disease-causing bacteria are responsible for a number of diseases including meningitis, pneumonia, tuberculosis, and several types of food-borne diseases. Bacteria: Helpful or Harmful? When all of the facts are considered, bacteria are more helpful than harmful. Humans have exploited bacteria for a wide variety of uses. Such uses include making cheese and butter, decomposing waste in sewage plants, and developing antibiotics. Scientists are even exploring ways for storing data on bacteria. Bacteria are extremely resilient and some are capable of living in the most extreme environments. Bacteria have demonstrated that they are able to survive without us, but we could not live without them.