What Are Five Ways Bacteria Can Be Harmful?

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A human body contains approximately 10 times as many bacteria as cells, according to the American Society for Microbiology. While most bacteria are relatively harmless or actually beneficial, there are some species that are detrimental to the human body.

Food Poisoning

Bacteria are the cause of many foodborne illnesses resulting from undercooked or unwashed food. Examples of these are Escherichia coli (E. coli) found in beef and unwashed vegetables and Salmonella enterica commonly found in chicken.

Wound Infection

Bacteria may also cause sepsis in untreated wounds and cuts. If left untreated, these infections can lead to loss of limbs and even death. Examples of these types of bacteria include Clostridium perfringens (gangrene) and Staphylococcus aureus (MRSA).

Other Infections

Bacteria may also enter the body through other means than cuts and lesions, resulting in a variety of infections and health problems. Helicobacter pylori is thought to be one of the leading causes of ulcers in humans. Respiratory problems, such as pneumonia and some sexually transmitted diseases, are also caused by bacterial strains.


Many forms of bacteria are found in untreated water which can result in severe harm to the human digestive tract and its local flora. Ingestion of these strains of bacteria may lead to flu-like symptoms, including diarrhea, vomiting and stomach cramps.


There are several strains of bacteria that act as plant pathogens. These strains may rapidly spread throughout crop populations, resulting in severe food shortages and economic issues for both consumers and farmers.