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Enteric Bacteria

What Are They, Effects on Health, and More

Author: Ali Syed, PharmD

Editors: Alyssa Haag, Ahaana Singh, Józia McGowan, DO, FACOI, FNAOME, CS

Illustrator: Jillian Dunbar

Copyeditor: Joy Mapes


What is enteric bacteria?

Enteric bacteria are bacteria that typically exist in the intestines of animals and humans. Enteric bacteria can be either harmless, such as gut flora or microbiota, or pathogenic, which means that they cause disease.

In general, all bacteria are classified depending on their type of cell wall (i.e., gram positive or gram negative) and their shape (i.e., rod, circular, or spiral shaped). Specifically, gram-positive bacteria have several layers of peptidoglycan, a material made of sugars and amino acids, in their cell wall, whereas gram-negative bacteria have only one peptidoglycan layer. There are various types of enteric bacteria that can be further classified according to their cell wall type and shape. 

What are the different types of enteric bacteria?

The intestines of all humans and animals are colonized by a large number of enteric bacteria. The majority of enteric bacteria are harmless and help maintain a healthy intestinal tract, and these are generally referred to as gut flora or human microbiota. However, other enteric bacteria are pathogenic, causing illness. For example, most strains of Escherichia coli (E. coli) are harmless, but the pathogenic strains of E.coli produce toxins that may lead to foodborne illnesses with various outcomes. For example, Escherichia coli O157:H7 is an enterohemorrhagic E.coli (EHEC) that can cause bloody diarrhea in infected individuals. Conversely, enterotoxigenic E.coli (ETEC) can cause non-bloody diarrhea. 

E. coli is one of the most studied species of Enterobacteriaceae within the microbiota. Enterobacteriaceae, a large family of gram-negative, rod-shaped bacteria, is the enteric bacteria family most frequently studied in medical microbiology. In addition to playing a significant role in the intestines, Enterobacteriaceae may be found in the genitourinary tract and can, in some cases, cause urinary tract infections. Klebsiella, Proteus, and Enterobacter are also notable Enterobacteriaceae species. 

Other types of pathogenic enteric bacteria include Salmonella, Shigella, Yersinia, Campylobacter jejuni (C. jejuni), and Clostridium difficile (C. diff), which is a gram-positive bacteria. The Shigella species has many pathogenic subtypes, including Shigella boydii (S. boydii), Shigella dysenteriae (S. dysenteriae), Shigella flexneri (S. flexneri), and Shigella sonnei (S. sonnei). 

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How does enteric bacteria enter the body?

Most often, enteric bacteria enters the body orally, generally through the consumption of food or water that is contaminated with animal or human feces. Other means of transmission include direct contact with contaminated water in swimming pools or lakes, contaminated surfaces, or feces from animals or individuals who harbor the bacteria.

The main mechanism through which E. coli O157:H7, Salmonella, and C. jejuni enter the body is through contaminated consumable products, including unpasteurized milk, undercooked meat, foods prepared in unsanitary conditions, and contaminated drinking water. Shigella can also enter the body through contaminated food and water, as well as through direct person-to-person or person-to-infected-animal contact. Yersinia pestis (Y. pestis) -- the cause of bubonic, septicemic, and pneumonic plague -- may be transmitted to humans by small infected mammals (e.g., rodents) and their fleas. C. diff bacteria are typically found in feces and may enter human bodies through direct contact with contaminated surfaces, particularly in healthcare environments. Infection with C. diff may also result from disruption of normal intestinal microbiota through antimicrobial use, such as taking prescription antibiotics, which can allow C. diff to colonize and overgrow, resulting in illness.

What happens when bacteria enter the body?

When pathogenic bacteria enter the body, they begin to multiply and cause infection. In response to infection, an individual’s immune system works to eliminate the pathogenic bacteria. In most individuals, the immune system is able to fight off the infection, so illness does not result. However, when the immune system cannot clear the infection, cells in the body can become damaged, and an individual may experience signs and symptoms of illness. 

The signs and symptoms of a bacterial illness vary depending on the specific type of bacteria involved and the particular location of infection. Some commonly experienced symptoms associated with enteric bacteria include fever, body ache, vomiting, diarrhea, and abdominal pain. 

Treatment for individuals infected with pathogenic bacteria varies depending on the type of bacteria causing the illness. In general, treatment may involve hydration and antimicrobial therapy, possibly including prescription antibiotic medication. Factors to consider when considering antimicrobial therapy include the type of pathogenic bacteria, the site of infection, and other individual-specific factors, such as the individual’s age, allergies, past medical history, and medication history. 

What are the most important facts to know about enteric bacteria?

Enteric bacteria are bacteria that exist in the intestines of animals and humans. Enteric bacteria are typically harmless and help maintain a healthy intestinal environment. However, certain strains of enteric bacteria may be pathogenic, causing illness in humans. Once bacteria enter the body, the immune system of some individuals can fight off the infection. However, in other individuals, the immune system cannot clear the infection, so illness occurs. Specific symptoms of an enteric bacteria infection vary based on the type of bacteria involved and the specific location of infection. Common signs and symptoms include fever, diarrhea, vomiting, and abdominal pain. Treatment for individuals infected with pathogenic bacteria usually involves keeping them hydrated and, depending on the type of bacterial infection, considering antimicrobial therapy.

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Related links

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Resources for research and reference

Centers for Disease Control and Prevention. (2014). E. coli (Escherichia coli): Questions and answers. Retrieved February 8, 2021, from https://www.cdc.gov/ecoli/general/index.html

Centers for Disease Control and Prevention. (2019, November 26). Plague: Frequently asked questions. Retrieved May 8, 2021, from https://www.cdc.gov/plague/faq/index.html 

Dekker, J., & Frank, K. (2015). Salmonella, Shigella, and Yersinia. Clinics in Laboratory Medicine, 35(2): 225-246. DOI: 10.1016/j.cll.2015.02.002

Kebede, A., Aragie, S., & Shimelis, T. (2017). The common enteric bacterial pathogens and their antimicrobial susceptibility pattern among HIV-infected individuals attending the antiretroviral therapy clinic of Hawassa university hospital, southern Ethiopia. Antimicrobial Resistance and Infection Control, 6: 128. DOI: 10.1186/s13756-017-0288-7

The National Academies of Sciences. (n.d.). How infection works: Encountering microbes; Entering the human host. In What You Need To Know About Infectious Disease. Retrieved on February 6, 2021, from http://needtoknow.nas.edu/id/infection/encountering-microbes/entering-the-human-host/ 

Todar, K. (2020). Bacterial pathogens of humans. In Todar's Online Textbook of Bacteriology.  Retrieved February 7, 2021, from http://textbookofbacteriology.net/medical_3.html

Todar, K. (2020). Structure and function of bacterial cells. In Todar's Online Textbook of Bacteriology.  Retrieved May 8, 2021, from http://www.textbookofbacteriology.net/structure_5.html 

University of California, Davis. (2020, February 12). Enteric bacteria. In UC Davis Safety Services: Occupational Health Surveillance System (OHSS). Retrieved February 7, 2021, from 

https://safetyservices.ucdavis.edu/units/occupational-health/surveillance-system/enteric-bacteria