Introduction to *Escherichia coli* (*E. coli*)
📌 *E. coli* is a well-researched member of the Enterobacteriaceae family, commonly found in the gastrointestinal (GI) tract of humans and animals as a commensal.
🦠 While generally harmless, certain strains of *E. coli* can cause illnesses such as food poisoning, urinary tract infections (UTIs), and pneumonia.
🌍 The primary habitat is the human GI tract, with secondary habitats including water, soil, and food.

Pathogenic *E. coli* Strains and Associated Illnesses
🔬 **STEC (Shiga Toxin-Producing *E. coli* / O157:H7): Causes bloody diarrhea and Hemolytic Uremic Syndrome (HUS) via Shiga toxin damaging vascular endothelial cells.
💧 ETEC (Enterotoxigenic *E. coli*): Responsible for traveler's diarrhea and watery diarrhea in children, producing heat-stable (ST) and heat-labile (LT) toxins that disrupt electrolyte absorption.
🦠 EIEC (Enteroinvasive *E. coli*):** Causes disease similar to shigellosis by invading epithelial cells, leading to inflammation, fever, and watery diarrhea.

Laboratory Identification and Culturing
🧪 *E. coli* is identified as oxidase-negative, catalase-positive, and indole-positive.
🟢 MacConkey Agar: *E. coli* ferments lactose, producing pink colonies.
⚫ EMB Agar: *E. coli* colonies exhibit a characteristic green metallic sheen.
🧬 Culturing often involves enrichment culture followed by subculturing on selective agar like EMB to isolate based on colony morphology and indicator color.

Versatility and Applications of *E. coli*
🧬 *E. coli* is a versatile organism, growing rapidly (doubling time around 30 minutes), making it an ideal model organism for genetics research.
🔬 Biotechnology: It is widely used in molecular biology to express proteins and produce compounds by accepting foreign genes via plasmids.
🍎 Food & Medicine: Used in the production of fermented foods (yogurt, cheese) and pharmaceuticals like antibiotics (e.g., using *E. coli* for large-scale drug production).

Treatment and Indicator Role
💊 Treatment for *E. coli* infections typically involves antibiotics such as beta-lactams (e.g., cefixime) or aminoglycosides (e.g., amikacin), depending on drug resistance profiles.
🚻 **UPEC (Uropathogenic *E. coli*):** Responsible for most UTIs, which are more prominent in females due to anatomical structure facilitating contamination.
🌊 *E. coli* serves as a key indicator bacteria in the coliform test to detect fecal contamination in water and food sources.

Key Points & Insights
➡️ Specific *E. coli* strains like STEC cause severe symptoms by releasing Shiga toxin, necessitating careful food handling, especially with undercooked ground beef.
➡️ The rapid growth and genetic adaptability of *E. coli* make it an economically viable tool in biotechnology for producing complex molecules and drugs at scale.
➡️ Laboratory identification relies on key biochemical tests: catalase positive and oxidase negative, alongside distinctive colony colors on selective media (pink on MacConkey, green metallic on EMB).
➡️ Poor hygiene is the primary underlying factor for outbreaks caused by most pathogenic *E. coli* types associated with food and waterborne illnesses.

📸 Video summarized with SummaryTube.com on Oct 15, 2025, 11:14 UTC