Diarrhoea is a common symptom of bacterial infections of the digestive system. That is why it is very difficult to identify the exact source of an infection, but the causes of infection may be different. In this post, we describe the most common bacteria in the digestive tract.

Enteroinvasive Escherichia coli (Shigella spp.)

Shigella spp./Enteroinvasive Escherichia coli (EIEC) causes an inflammation that causes symptoms clinically reminiscent of bacterial dysentery. Bacteria actively penetrate the cells of the colon epithelium, causing ulceration of the mucosa and diarrhoea. Due to the invasive mechanism of action, metabolic features (inability to ferment lactose) and genetic features (presence of a large plasmid), EIEC strains are related to Shigella. The ShET-2 toxin encoded by the plasmid gene is responsible for the excretion of fluid into the intestinal lumen and blocking its reabsorption, which is the cause of watery diarrhoea. Shigella spp. is a bacillus that evolved from the genus Escherichia and causes symptoms of shigellosis – dysentery. They are highly infectious pathogens that do not die in the acidic stomach contents. They colonize the distal part of the small intestine and colon, causing inflammation and ulceration. Usually, the infection clears up on its own without treatment. In a few cases (especially in infants), absorption from the intestine into the bloodstream of Shiga exotoxin (ShT) causes the infection to become generalized (coma, convulsions, haemolytic uremic syndrome). ShT inhibits the protein biosynthesis in cells, which leads to their death.
Clinical symptoms: watery diarrhoea, presence of mucus and blood in the stools, abdominal pain, fever and malaise, and sometimes nausea and vomiting.

Campylobacter genus

Campylobacter spp. is a bacillus that cause acute diarrhoea called campylobacteriosis, diagnosed mainly in childhood. The disease provides partial immunity, therefore the frequency and percentage of symptomatic infections decrease with age. For this reason, many infections in adults are asymptomatic or very mild. Bacteria of the genus Campylobacter are found in the digestive tract of many slaughtered animals, therefore the most common route of infection is the consumption of poorly heat-treated meat.

Clinical symptoms: watery diarrhoea, often bloody, persistent abdominal pain, fever, headache, muscle aches and malaise.

Yersinia

Yersinia enterocolitica causes a disease called yersiniosis. After penetrating the lumen of the small intestine, bacteria enter the lymphatic system at the end of the ileum, where they multiply and then penetrate the blood. Most infections affect children under 5 years of age. Infections range from mild diarrhoea through severe infections with fever and severe abdominal pain suggesting appendicitis, to systemic infections (e.g. Reiter’s syndrome, erythema nodosum). The Yersinia genus is an invasive pathogen with intoxicating properties – they produce Yst enterotoxin. The infection is spread through food (undercooked pork), milk and water. Most cases of the disease occur in autumn and winter.

Clinical symptoms: in young children: mild fever, cramping abdominal pain, loose stools, often with an admixture of mucus and/or blood, and vomiting, in older children and adults: abdominal pain located on the right side and fever.

Vibrio

Vibrio spp. in healthy people may cause mild symptoms of gastroenteritis, while in people with chronic diseases such as liver disease, alcoholism, diabetes, haemochromatosis and HIV/AIDS, may cause sepsis. Most of the Vibrio strains responsible for human infections synthesize a heat-residual cytotoxin and are capable of invading intestinal epithelial cells. Vibrio cholerae is particularly dangerous because, after reaching the small intestine, it colonizes the intestinal mucosa and synthesizes the heat-labile enterotoxin LT, which disrupts the functioning of enterocytes and is responsible for the massive loss of water and electrolytes. Massive water loss quickly leads to dehydration, the development of metabolic acidosis, hypokalemia and shock. If untreated, 40-60% of the cases are fatal.

Clinical symptoms – mild form: rapid, watery diarrhoea, nausea, abdominal pain, less frequently: vomiting, fever, headache, chills; acute form: haemorrhagic gastroenteritis, bloody diarrhoea.

Clostridium difficile

The Clostridium difficile strain carrying the toxin B gene is the etiological factor of colitis pseudomembranaceae. When the natural microbiota is destroyed with antibiotic therapy, C. difficile bacilli multiply and colonize the intestine. The following toxins are responsible for the pathogenic effect of C. difficile in the gastrointestinal tract: toxin A (enterotoxin), and toxin B (cytotoxic). Toxins are responsible for the symptoms that occur.

Clinical symptoms: enteritis, increased production of intestinal mucus and fluid, damage to the intestinal mucosa, severe diarrhoea, colitis.

Aeromonas

Aeromonas spp. are bacteria commonly found in fresh and salt water. They cause gastroenteritis, usually after consuming contaminated water or food, and can cause wound infections from contact with contaminated water. In healthy people, they cause only diarrhoea, while in immunocompromised people, they can cause opportunistic systemic infection.

Clinical symptoms: diarrhoea.

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