Almost every human will experience, at some stage in their life, an episode of diarrhoea due to a bacterial infection of the gastrointestinal tract. There are a variety of protective mechanisms in place, such as the high acid content of the stomach, to reduce the risk of such infections, but bacteria have evolved a variety of virulence factors, such as adhesion molecules and toxins, that enable active infections to take place. Enterotoxins, such as the cholera toxin, can cause a net secretion of water into the small bowel lumen, overwhelming the absorptive capacity of the large bowel. Cytotoxins can cause damage to the large bowel mucosa, leading to marked inflammation and causing bloody diarrhoea. Most cases of gastroenteritis can be treated with rehydration alone, but in some circumstances specific antimicrobial therapy is needed. This article highlights the pathogens implicated, the symptoms that usually result and the way such infections are managed.

Key Concepts:

• Gastrointestinal infections due to bacteria are very common.
  
• Bacteria that cause infection of the gastrointestinal tract have developed a variety of virulence factors, including adhesion molecules and toxin secretion.
  
• Although most bacterial toxins are produced in the gut after infection, some are ingested preformed in food.
  
• Watery diarrhoea is usually the result of enterotoxins acting in the small bowel, causing net secretion of water and electrolytes into the lumen.
  
• Dysentery is bloody diarrhoea caused by bacteria that have caused inflammation in the large bowel mucosa.
  
• Although Campylobacter species are the most common cause of sporadic bacterial food poisoning, more outbreaks are caused by Salmonella species.
  
• Clostridium difficile has, in the past decade, become an important healthcare-associated infection in hospitals in developed countries.
  
• Enterotoxigenic E. coli (ETEC) is a very common cause of travellers’ diarrhoea.
  
• Most cases of diarrhoea due to bacteria can be treated with rehydration therapy alone.
  
• Although some bacterial infections of the gastrointestinal tract require specific antibiotic therapy, empiric therapy should only be given in certain circumstances to vulnerable patients to minimise overuse of antimicrobials.