Disease caused by Enterobacteriaceae: E. coli Urinary tract infection, E coli–associated diarrheal diseases: EPEC, ETEC, STEC, EIEC, EAEC.

Question 1

E. coli Urinary Tract Infection (UTI)

Answer 1

E. coli is the most common cause of urinary tract infections, accounting for around 80-90% of all cases. Uropathogenic E. coli (UPEC) strains possess virulence factors such as adhesins (e.g., P pili) that enable attachment to uroepithelial cells, as well as toxins like hemolysin. These factors allow E. coli to colonize the urinary tract, leading to cystitis, pyelonephritis, and, in severe cases, bacteremia. Diagnosis is based on urine culture, with identification of >10^5 CFU/mL of E. coli. Treatment typically involves antibiotics such as trimethoprim-sulfamethoxazole or ciprofloxacin.

Question 2

EPEC (Enteropathogenic E. coli)

Answer 2

EPEC is a major cause of diarrhea in infants, especially in developing countries. It adheres to enterocytes through a type III secretion system (T3SS) and induces a characteristic ‘pedestal’ formation on the intestinal surface. EPEC disrupts the microvilli and causes cell apoptosis, leading to malabsorption and diarrhea. The disease is characterized by watery diarrhea, vomiting, and fever. Diagnosis involves detection of the intimin gene (eae) through PCR or serotyping. Treatment is supportive, with rehydration and sometimes antibiotics.

Question 3

ETEC (Enterotoxigenic E. coli)

Answer 3

ETEC causes traveler’s diarrhea and is associated with contaminated water or food. ETEC produces two major toxins: heat-labile toxin (LT) and heat-stable toxin (ST). LT increases cyclic AMP levels, leading to secretion of electrolytes and water into the intestinal lumen, while ST increases cyclic GMP, causing similar effects. This results in watery diarrhea, cramps, and nausea. Diagnosis is based on detection of LT and ST genes by PCR. Treatment involves rehydration and, in some cases, antibiotics like azithromycin.

Question 4

STEC (Shiga toxin-producing E. coli)

Answer 4

STEC, particularly E. coli O157:H7, produces Shiga toxins (Stx1 and Stx2), which inhibit protein synthesis, leading to cell death. This toxin can cause hemorrhagic colitis, characterized by bloody diarrhea and abdominal pain. In severe cases, it can lead to hemolytic uremic syndrome (HUS), a life-threatening condition marked by hemolysis, thrombocytopenia, and kidney failure. Diagnosis is made by detecting Shiga toxins in stool samples. Supportive care is critical, and antibiotics are generally avoided due to the risk of triggering HUS.

Question 5

EIEC (Enteroinvasive E. coli)

Answer 5

EIEC causes a dysentery-like illness, with symptoms such as bloody diarrhea, fever, and abdominal cramps. EIEC invades and replicates within the epithelial cells of the colon, similar to Shigella species. It induces cell death and inflammation, leading to the classic dysentery presentation. Diagnosis is through stool culture and PCR for invasion-related genes. Treatment is typically supportive, though antibiotics like ciprofloxacin may be used in severe cases.

Question 6

EAEC (Enteroaggregative E. coli)

Answer 6

EAEC causes persistent diarrhea, especially in children and immunocompromised individuals. EAEC adheres to the intestinal mucosa in a distinctive ‘stacked brick’ pattern, producing enterotoxins and cytotoxins that contribute to its pathogenicity. It causes watery diarrhea, abdominal pain, and nausea. Diagnosis involves identifying the aggregative adherence pattern and detecting EAEC-specific virulence genes through PCR. Treatment is supportive, with rehydration and, in some cases, antibiotics.