Bacterial gastrointestinal illness may result from infection by living bacteria or intoxication by toxins already present in food. This lesson introduces that distinction and examines two important foodborne diseases: staphylococcal food poisoning and shigellosis.
In a foodborne infection, a person ingests microbes that colonize the gut and then produce toxins or otherwise damage host tissues. In a foodborne intoxication, bacteria produce the toxin in food before it is eaten. In both cases, toxins can harm cells lining the gastrointestinal tract, often causing diarrhea, watery stool, abdominal cramps, nausea, and vomiting. Dysentery—diarrhea that may contain blood or mucus—is a more severe presentation.
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How do foodborne infection and intoxication differ?
In infection, ingested microbes colonize the gut and produce toxins or cause tissue injury. In intoxication, bacteria made the toxin in food before it was eaten; viable bacteria need not remain for symptoms to occur.
What causes the rapid onset of staphylococcal food poisoning?
A person ingests preformed *S. aureus* enterotoxin. Symptoms often begin within one to six hours and commonly include nausea, vomiting, cramps, and diarrhea.
Why may reheating fail to make food containing staphylococcal toxin safe?
The enterotoxins are heat stable and resistant to low pH. Heat may kill *S. aureus* without reliably destroying toxin already present.
How does shigellosis spread and damage the intestine?
It spreads mainly by the fecal–oral route. *Shigella* invades intestinal epithelial cells, multiplies inside them, and spreads to adjacent cells, causing inflammation and ulceration.
What is the significance of Shiga toxin in severe shigellosis?
Shiga toxin interferes with protein synthesis in endothelial cells. Vascular injury can cause intestinal hemorrhage and kidney glomerular damage that may lead to HUS.
Quiz questions
How does cholera toxin cause profuse watery diarrhea?Answer: It increases intracellular cAMP, promoting chloride and electrolyte secretion into the intestinal lumen.
Why is serotyping useful when investigating *Salmonella* disease?Answer: Serotypes are associated with different disease patterns and can inform public-health investigations and treatment decisions.
How do Tir and Intimin help EPEC attach to intestinal cells?Answer: EPEC injects Tir into host cells, where it acts as a receptor for bacterial Intimin.
Why are antibiotics generally avoided in EHEC infection?Answer: Bacterial killing may release Shiga-like toxin and increase the risk of hemolytic uremic syndrome.
What can allow *Clostridioides difficile* to overgrow in the gut?Answer: Antibiotic-associated disruption of the normal gut microbiota can permit its overgrowth.
Based on Microbiology by Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Philip Lister, Brian M. Forster (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.