Escherichia coli (E. coli)

• Escherichia coli (E. coli) is linked to gastroenteritis (diarrhea), urinary tract infections (UTIs), meningitis, and sepsis.
• E. coli, a gram-negative rod, is a facultative anaerobe found in the colon and feces.
• E. coli is encapsulated, motile, and ferments lactose, producing pink colonies on MacConkey agar.
• E. coli is oxidase negative and catalase positive and ferments glucose.
• Eosin methylene blue agar shows green-sheen colonies.
• Large numbers of E. coli exist in the GI tract, acting as an opportunistic pathogen causing GI and extraintestinal diseases when the intestines are perforated.
• Most E. coli infections are endogenous, excluding neonatal meningitis and gastroenteritis.
• Transmission occurs from the birth canal to neonates, potentially leading to neonatal meningitis.
• E. coli is a normal part of the human intestinal microbiota; some strains are opportunistic pathogens.
• Traveler’s diarrhea is often caused by ingesting food and water contaminated with human feces.
• Consuming undercooked beef can lead to enterohemorrhagic E. coli O157 infection, as cattle are a reservoir.

Pathotypes & Toxins

• Enterotoxigenic E. coli (ETEC) secretes toxins which leads to traveler’s diarrhea.
• ETEC enterotoxins affect cells in the jejunum and ileum.
• Heat-labile toxin from ETEC increases cAMP causing watery diarrhea.
• Heat-stable toxin from ETEC stimulates guanylate cyclase causing watery diarrhea.
• ETEC-related diarrhea is watery, non-bloody, and of short duration.
• Enteropathogenic E. coli (EPEC) causes infant diarrhea.
• EPEC adheres to host cells via bundle-forming pili, disrupting microvillus structure, leading to malabsorption and diarrhea.
• Enteroaggregative E. coli (EAEC) causes persistent diarrhea, especially in children and immunocompromised individuals.
• EAEC aggregates, adheres to intestinal mucosa, produces enterotoxins and cytotoxins, and causes diarrhea.
• Shiga-like Toxin-Producing E. coli (STEC) causes hemorrhagic colitis (bloody diarrhea) and hemolytic uremic syndrome (HUS).
• STEC removes an adenine from ribosomal RNA, halting protein synthesis, in bloody diarrhea.
• E. coli O157 has a low ID50 (infectious dose) of about 100 organisms.
• STEC can lead to kidney failure, hemolytic anemia, and thrombocytopenia.
• Enteroinvasive E. coli (EIEC) causes dysentery-like illness (bloody diarrhea with mucus and pus).
• EIEC invades the large intestine's epithelium, causing bloody diarrhea with neutrophils in the stool.

Uropathogens

• Uropathogens cause UTIs by colonizing and infecting the urethra, bladder, ureters, or kidneys. Pili and fimbriae help uropathogens adhere to the jejunum and ileum.
• Cranberry juice, containing flavonoids, inhibits pili from binding to receptors.
• Secreted endotoxin (LPS) from E. coli can cause sepsis, leading to fever, hypotension, and DIC (disseminated intravascular coagulation).
• E. coli is a frequent cause of nosocomial UTIs, often due to urinary catheters.
• If only the bladder is impacted, it is called cystitis.
• Kidney infection is called pyelonephritis.

Virulence Factors & Pathogenesis

• Pili mediate adherence of E. coli to cells in the jejunum and ileum.
• Endotoxins secreted by enterotoxigenic E. coli (ETEC) act on jejunum and ileum cells.
• Heat-labile toxin increases cAMP and causes watery diarrhea.
• Heat-stable toxin stimulates guanylate cyclase causing watery diarrhea.
• Enteroinvasive E. coli (EIEC) invades the epithelium of the large intestine, leading to bloody diarrhea accompanied by neutrophils.
• Shiga-like toxin (verotoxin) produced by STEC removes adenine from ribosomal RNA, inhibiting protein synthesis.
• E. coli O157 serotype has a low infectious dose (ID50) of about 100 organisms.
• Shiga-like toxin can cause hemolytic uremic syndrome (HUS) if it enters the bloodstream.
• Certain E. coli strains bind to receptors on the urinary tract epithelium using pili.
• The motility of E. coli facilitates its ascent through the urethra, bladder, ureter, and kidneys.
• Capsule polysaccharide interferes with phagocytosis, whereas endotoxin causes systemic diseases like neonatal meningitis.
• Enteroaggregative E. coli (EAEC) aggregates and binds to intestinal mucosa, releasing enterotoxins and cytotoxins that cause diarrhea.
• Enteropathogenic E. coli (EPEC) binds to host cells using bundle-forming pili, which disrupts microvillus structure resulting in malabsorption and diarrhea.

Clinical Manifestations

• Diarrhea caused by enterotoxigenic E. coli (ETEC) is generally watery, non-bloody, self-limiting, and of short duration.
• ETEC-related diarrhea is often associated with travel, hence the term "traveler's diarrhea."
• Infection with enterohemorrhagic E. coli (EHEC) results in a dysentery-like syndrome characterized by bloody diarrhea, abdominal cramping, and fever.
• Shiga-like toxin-producing E. coli (STEC) strains cause bloody diarrhea, which can be complicated by hemolytic uremic syndrome (HUS).
• Hemolytic uremic syndrome (HUS) is characterized by kidney failure, hemolytic anemia, and thrombocytopenia.
• E. coli is a common cause of community-acquired urinary tract infections (UTIs), primarily in women.
• E. coli is the most frequent cause of nosocomial UTIs, often associated with indwelling urinary catheters.
• If only the bladder is involved, the condition is called cystitis, while infection of the kidney is termed pyelonephritis.
• Along with Group B Streptococcus, E. coli is a major cause of meningitis and sepsis, particularly in neonates.

Diagnosis & Treatment

• Stool, urine, blood, or CSF samples can be used for an E. coli diagnosis, depending on the type of disease suspected.
• Gram staining can be performed on stool or urine samples; cultures on eosin-methylene blue agar can confirm the diagnosis.
• On eosin-methylene blue agar, E. coli colonies have a characteristic green sheen.
• Most E. coli strains do not produce hemolysis on blood agar.
• Culture on MacConkey agar demonstrates pink colonies due to lactose fermentation.
• EHEC O157:H7 strains of E. coli do not ferment sorbitol.
• E. coli are generally indole-positive, catalase-positive, and oxidase-negative.
• Hemolytic uremic syndrome (HUS) can be confirmed by identifying Shiga-like toxin in the blood.
• Antibiotic therapy is generally not indicated for E. coli diarrheal diseases.
• Cystitis can be treated with oral trimethoprim-sulfamethoxazole or nitrofurantoin.
• Pyelonephritis can be treated with ciprofloxacin or ceftriaxone.
• Sepsis can be treated with a third-generation cephalosporin, such as cefotaxime, with or without an aminoglycoside, such as gentamicin.
• For neonatal meningitis treatment, a combination of ampicillin and cefotaxime is typically administered.