Common bacteria in diarrhea
Reading File
Finding Sources
Finding Sources
Reading File
Reading File
Reading File
Reading File
Finding Sources
Finding Sources
Reading File
Here is a comprehensive overview of the common bacteria that cause diarrhea, drawn from Harrison's Principles of Internal Medicine (2025), Frameworks for Internal Medicine, Yamada's Gastroenterology, and Quick Compendium of Clinical Pathology.
Common Bacteria in Diarrhea
Bacterial diarrhea is broadly divided into noninflammatory (watery/secretory) and inflammatory (invasive/dysenteric) types based on mechanism.
Noninflammatory (Watery/Secretory) Diarrhea
These bacteria act via toxins without invading the gut wall. Stools are watery, typically without blood or pus, and fever is usually absent or mild.
| Organism | Key Features |
|---|---|
| Vibrio cholerae | Profuse "rice-water" stools; choleratoxin activates adenylyl cyclase, causing massive Cl⁻ secretion; life-threatening dehydration; Asia, Africa, Latin America |
| Enterotoxigenic E. coli (ETEC) | #1 cause of traveler's diarrhea; produces heat-labile (LT) and heat-stable (ST) toxins; rapid-onset watery diarrhea 1-3 days after arrival in endemic areas |
| Enteropathogenic E. coli (EPEC) | Attaches to intestinal epithelium and effaces microvilli (A/E lesion); important in infant diarrhea in developing countries |
| Staphylococcus aureus | Preformed enterotoxin; onset within 30 min - 6 hours; prominent vomiting + cramps; often from improperly stored cooked foods; shortest incubation of all |
| Clostridium perfringens | Toxin-mediated; onset 8-12 hours; watery diarrhea + intense cramps; classically from meat/poultry; resolves in <24 hours |
| Bacillus cereus | Two syndromes: (1) emetic form - vomiting within 30 min - few hours (fried rice classic source); (2) diarrheal form - watery diarrhea 6-15 hours post-ingestion |
| Clostridioides difficile | Antibiotic-associated; toxins A (enterotoxin) + B (cytotoxin); ranges from mild diarrhea to fulminant pseudomembranous colitis; spore-forming gram-positive rod |
| Listeria monocytogenes | Mainly affects immunocompromised, elderly, pregnant; watery diarrhea; gram-positive rod; transmitted via unpasteurized dairy, deli meats |
Inflammatory (Invasive/Dysenteric) Diarrhea
These bacteria invade the intestinal mucosa. Classically cause bloody/mucoid stools, fever, tenesmus, and neutrophils in stool. Campylobacter, Shigella, Salmonella, E. coli (invasive strains) are the leading causes.
| Organism | Key Features |
|---|---|
| Shigella spp. | Classic dysentery pathogen; invades colonic epithelium + spreads cell-to-cell; Shiga toxin (in S. dysenteriae) can cause HUS; small infectious dose (10-100 organisms) |
| Campylobacter jejuni | Most common bacterial cause of diarrhea in many developed countries; watery then bloody diarrhea; poultry, unpasteurized milk; incubation 2-5 days; post-infectious complication: Guillain-Barre syndrome |
| Salmonella spp. (non-typhoidal) | Undercooked poultry/eggs; fever + nausea + diarrhea (6-48 hrs); bacteremia risk in sickle cell, immunocompromised; can cause reactive arthritis post-infection |
| Enterohemorrhagic E. coli (EHEC/STEC) O157:H7 | Shiga toxin-producing; undercooked ground beef; bloody diarrhea without fever is classic; most important complication: hemolytic uremic syndrome (HUS) - microangiopathic hemolytic anemia + thrombocytopenia + AKI; diagnosed on sorbitol-MacConkey agar |
| Yersinia enterocolitica | Causes mesenteric adenitis mimicking appendicitis; milk, pork; incubation up to 7 days; cold enrichment technique for culture |
| Enteroinvasive E. coli (EIEC) | Invades colonic epithelium similar to Shigella; dysentery syndrome |
| Aeromonas and Vibrio parahaemolyticus | Seafood-associated; watery or bloody diarrhea |
Quick Summary Table: Noninflammatory vs. Inflammatory
| Feature | Noninflammatory | Inflammatory |
|---|---|---|
| Stool | Watery, large volume | Small volume, bloody/mucoid |
| Fever | Absent or low | Usually present |
| Fecal leukocytes | Absent | Present |
| Site | Small bowel | Large bowel (colon) |
| Key organisms | ETEC, V. cholerae, S. aureus, C. perfringens, B. cereus, C. difficile | Shigella, Campylobacter, Salmonella, EHEC, Yersinia |
Incubation Time (Onset After Exposure)
| Organism | Onset |
|---|---|
| S. aureus | <6 hours |
| C. perfringens | 8-16 hours |
| B. cereus | 10-16 hours |
| Salmonella | 6-48 hours |
| ETEC | 1-3 days |
| EHEC | 1-8 days |
| Campylobacter jejuni | 2-5 days |
| Shigella | 4-7 days |
- Quick Compendium of Clinical Pathology, p. 98
- Frameworks for Internal Medicine, p. 197
- Harrison's Principles of Internal Medicine 22E (2025), Ch. 138
Differentiate small bowel and large bowel diarrhea
Finding Sources
Finding Sources
Reading File
Finding Sources
The textbook table from Family Medicine gives an excellent breakdown. Let me now present the full comparison.
Small Bowel vs. Large Bowel Diarrhea
About 90% of acute community-acquired infectious diarrhea in the US is small bowel diarrhea, while only 5-10% represents large bowel diarrhea (the dysentery syndrome). The distinction is both conceptually and clinically important, though there is considerable overlap.
Comparison Table
| Parameter | Small Bowel Diarrhea | Large Bowel Diarrhea |
|---|---|---|
| Medical synonym | Noninflammatory diarrhea | Inflammatory diarrhea (dysentery) |
| Stool character | Watery, large volume | Semiformed/small volume, mucus + blood |
| Stool frequency | Infrequent (few times/day) | Frequent (many times/day) |
| Tenesmus | Absent | Often present (painful rectal spasms) |
| Pain on defecation | Usually absent | Often present |
| Site of pain | Periumbilical or diffuse (midabdomen) | Lower abdominal / hypogastric |
| Fever | Absent or mild | Usually present (suggests invasion) |
| Blood/mucus in stool | Absent | Often present |
| Fecal leukocytes | Absent | Present |
| Urgency | May occur due to large volume | Marked urgency with small-volume output |
| Dehydration risk | High (large fluid losses) | Lower (small volume per episode) |
| Diagnostic yield of stool culture | Low (discouraged routinely) | Higher yield - cultures indicated |
| Antimotility agents | Generally safe | Contraindicated (can worsen colitis, risk HUS in STEC) |
Pathophysiology
Small Bowel Diarrhea
The small bowel secretes excessive fluid or fails to absorb it. Because the colon still functions normally as a reservoir, it can store a large volume of fluid until it becomes overdistended - this then prompts an urgent but infrequent bowel movement. The result is large-volume, watery stools.
Mechanisms include:
- Secretory: Toxins (cholera, ETEC) activate adenylyl cyclase → increased cAMP → Cl⁻ secretion and Na⁺/water follows
- Osmotic: Unabsorbed solutes draw water into the lumen (e.g., lactase deficiency, Giardia)
- Malabsorptive: Villous damage (rotavirus, Giardia, celiac) reduces absorptive surface area
Large Bowel Diarrhea
The colon is directly inflamed - its reservoir function is lost. The irritated mucosa cannot absorb water and produces mucus and exudate. Each spasm of the inflamed colon expels small amounts of stool, mucus, and blood. Tenesmus arises from rectal inflammation and the constant urge to defecate.
Mechanisms include:
- Inflammatory/invasive: Bacteria invade the mucosa (Shigella, Campylobacter, Salmonella, EIEC)
- Cytotoxic: Toxins destroy colonocytes (C. difficile toxin B, Shiga toxin)
Causative Organisms
| Small Bowel (Noninflammatory) | Large Bowel (Inflammatory) |
|---|---|
| Vibrio cholerae | Shigella spp. |
| ETEC | Campylobacter jejuni |
| Staphylococcus aureus | Non-typhoidal Salmonella |
| Clostridium perfringens | EHEC (O157:H7) |
| Bacillus cereus | Clostridioides difficile |
| Viruses (rotavirus, norovirus) | Yersinia enterocolitica |
| Giardia lamblia | Entamoeba histolytica |
Key Clinical Clue
Bloody diarrhea = large bowel source until proven otherwise. Think: Shigella, Campylobacter, EHEC, Salmonella, C. difficile. Fecal leukocytes support an inflammatory (large bowel) process.
"Rice-water" stools = classic small bowel (secretory) diarrhea, most notably cholera.
- Textbook of Family Medicine 9e, Table 15-7, p. 276
This is a shared conversation. Sign in to Orris to start your own chat.