Explain how bacteria can be both harmful and helpful.

The species of bacteria that colonize our respiratory and digestive systems help set up checks and balances in the immune system. White blood cells police the body, looking for infections, but they also limit the amount of bacteria that grow there. Likewise, bacteria keep white blood cells from using too much force. Bacteria also help out by doing things cells are ill-equipped to do. For instance, bacteria break down carbohydrates (sugars) and toxins, and they help us absorb the fatty acids which cells need to grow. Bacteria help protect the cells in your intestines from invading pathogens and also promote repair of damaged tissue. Most importantly, by having good bacteria in your body, bad bacteria don’t get a chance to grow and cause disease.

Some species of bacteria in your body can result in diseases, such as cancer, diabetes, cardiovascular disease, and obesity. Usually, these diseases happen only when the normal microbiome is disrupted, but that can occur even from antibiotics. Antibiotics kill bacteria, and some of those will be good bacteria that we need to protect our health. When that happens, the bad bacteria that normally are kept in check have room to grow, creating an environment ripe for disease.

Bad bacteria can exist at low levels in your body without causing harm or can grow too much and wreak havoc. Staphylococcus aureus can cause something as simple as a pimple or as serious as pneumonia or toxic shock syndrome. P. gingivalis can cause gum disease, and was recently linked to pancreatic cancer (read our article find out more). Similarly, when not suppressed by good bacteria, Klebsiella pneumonia can cause colitis, and subsequently lead to colorectal cancer.

In addition to allowing disease-causing bacteria to flourish, the elimination of good bacteria throws  the immune system out of whack. The result can be simple allergies or very debilitating autoimmune diseases. Without the right balance of bacteria, your body might suffer from constant inflammation.

Inflammation is the body’s alarm system, which calls white blood cells to heal a wound or to get rid of infection. Chronic inflammation, however, can make the body more susceptible to autoimmune diseases and cancer, such as causing inflammatory bowel disease which if uncontrolled can cause colon cancer.

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