Bacterial gut pathogens (salmonella, campylobacter, EHEC)

Salmonella, shigella, campylobacter, yersinia and enterohaemorrhagic Escherichia coli (EHEC, including E. coli O157) are bacteria that cause acute gut infections with diarrhoea. They are detected in stool – by culture in the laboratory, by detecting their genetic material using PCR or, for EHEC, via the Shiga toxins and their genes. The PCR also picks up enteroinvasive E. coli (EIEC). Clostridioides difficile, which causes diarrhoea mainly after antibiotics, and single-celled parasites are described on their own pages. Detection of these pathogens is notifiable in Germany; the laboratory reports it to the public health office.

How bacterial gut pathogens attack the gut lining

The pathogens are usually taken up via food, water or contact with infected people or animals and have to survive stomach acid. After that they proceed in different ways. Salmonella and yersinia invade the lining mainly in the lower small intestine, yersinia also the lymph nodes of the gut. Shigella and enteroinvasive E. coli infect the cells of the colon lining, multiply inside them and spread from cell to cell; very few shigella are enough for infection. Campylobacter moves through the mucus with its flagella and damages the lining of the small intestine and colon. In all cases the bacteria attract immune cells, the lining becomes inflamed and releases water and salts.

What happens with a salmonella, campylobacter or shigella infection?

Diarrhoea, abdominal cramps, nausea and fever usually begin after a few hours to days. Fluid and salts are lost through the inflamed lining, which can strain the circulation, especially in small children and older people. If the pathogens attack the colon wall, as shigella or campylobacter do, blood and mucus may appear in the stool. Through inflamed lymph nodes in the lower right abdomen, yersinia sometimes cause pain resembling appendicitis. Most infections clear up on their own; salmonella, however, can still be shed in stool for weeks afterwards. Campylobacter is the most frequently reported bacterial cause of diarrhoea in Germany.

What do EHEC and Shiga toxins do in the body?

EHEC attach to the colon lining and produce Shiga toxins. These toxins enter the cells, shut down protein production there and damage the walls of small blood vessels – in the gut this often results in bloody diarrhoea. If the toxins reach the circulation, they can attack the vessels of the kidneys in particular: in haemolytic uraemic syndrome (HUS), red blood cells are destroyed, platelets fall and the kidneys work less well. Children are particularly affected. EHEC is transmitted mainly via raw milk, undercooked beef and contaminated vegetables or sprouts; ruminants often carry the pathogen without symptoms. E. coli O157 is the best-known EHEC type.

No gut pathogens detected – what does it mean?

Without detection, the bacteria tested for are an unlikely cause of the current diarrhoea. Diarrhoea can equally be caused by viruses such as noro- or rotaviruses, by single-celled parasites, by Clostridioides difficile or by non-infectious causes. Because the pathogens are usually shed only during and shortly after the illness, a later stool test mostly no longer shows a past infection. Studies have observed persistent irritable bowel symptoms more often after bacterial gut infections; less often, joint inflammation (reactive arthritis) or – after campylobacter – nerve inflammation (Guillain-Barré syndrome) occurs weeks later.

The interpretation is given in your report.