Escherichia coli
Introduction
Escherichia coli, commonly known as E. coli, is a type of bacterium that normally lives in the
intestines of humans and animals. It is one of the most well-studied microorganisms in the field
of Microbiology.
Key Features:
• Shape and Type: Rod-shaped, Gram-negative bacterium.
• Habitat: Primarily found in the lower intestine (gut flora).
• Oxygen Requirement: Facultative anaerobe (can survive with or without oxygen).
• Motility: Many strains can move using flagella.
Importance:
• Beneficial Role: Most E. coli strains are harmless and help with digestion, vitamin K
production, and preventing harmful bacteria from colonizing the gut.
• Scientific Use: Widely used in laboratories for research, biotechnology, and genetic
engineering because of its simple structure and rapid growth.
Harmful Strains:
Some strains can cause illness. For example, E. coli O157:H7 infection can lead to severe
food poisoning, causing symptoms like diarrhea (sometimes bloody), stomach cramps,
and vomiting.
Transmission:
• Contaminated food (undercooked meat, unpasteurized milk).
• Contaminated water.
• Poor hygiene or sanitation.
Morphology of Escherichia coli
E. coli is a rod-shaped (bacillus) bacterium with the following morphological characteristics:
• Size: Typically about 1–3 µm long and 0.4–0.7 µm wide.
• Shape: Straight rods, sometimes occurring singly or in pairs.
, • Cell Wall: Gram-negative, with a thin peptidoglycan layer and an outer membrane.
• Arrangement: Usually single; may form short chains.
• Motility: Most strains are motile with peritrichous flagella (flagella distributed all
around the cell).
• Capsule: Some strains possess a capsule (protective outer layer).
• Spores: Non-spore forming.
• Fimbriae (Pili): Present in many strains, helping in attachment to surfaces.
Classification of E. coli Pathotypes
Escherichia coli strains that cause disease are classified into. pathotypes based on their
virulence factors, mechanisms of infection, and clinical symptoms.
1. Enteropathogenic E. coli (EPEC)
• Causes infant diarrhea.
• Adheres to intestinal cells and disrupts microvilli.
2. Enterotoxigenic E. coli (ETEC)
• Common cause of traveler’s diarrhea.
• Produces heat-labile (LT) and heat-stable (ST) toxins.
3. Enterohemorrhagic E. coli (EHEC)
• Causes bloody diarrhea and hemorrhagic colitis.
• Produces Shiga toxin (e.g., O157:H7 strain).
4. Enteroinvasive E. coli (EIEC)
• Invades intestinal epithelial cells.
• Causes dysentery-like illness similar to Shigella.
5. Enteroaggregative E. coli (EAEC)
• Forms a “stacked-brick” pattern on intestinal mucosa.
• Causes persistent diarrhea, especially in children.
6. Diffusely Adherent E. coli (DAEC)
• Shows diffuse adherence to epithelial cells.
• Associated with mild diarrhea.
Introduction
Escherichia coli, commonly known as E. coli, is a type of bacterium that normally lives in the
intestines of humans and animals. It is one of the most well-studied microorganisms in the field
of Microbiology.
Key Features:
• Shape and Type: Rod-shaped, Gram-negative bacterium.
• Habitat: Primarily found in the lower intestine (gut flora).
• Oxygen Requirement: Facultative anaerobe (can survive with or without oxygen).
• Motility: Many strains can move using flagella.
Importance:
• Beneficial Role: Most E. coli strains are harmless and help with digestion, vitamin K
production, and preventing harmful bacteria from colonizing the gut.
• Scientific Use: Widely used in laboratories for research, biotechnology, and genetic
engineering because of its simple structure and rapid growth.
Harmful Strains:
Some strains can cause illness. For example, E. coli O157:H7 infection can lead to severe
food poisoning, causing symptoms like diarrhea (sometimes bloody), stomach cramps,
and vomiting.
Transmission:
• Contaminated food (undercooked meat, unpasteurized milk).
• Contaminated water.
• Poor hygiene or sanitation.
Morphology of Escherichia coli
E. coli is a rod-shaped (bacillus) bacterium with the following morphological characteristics:
• Size: Typically about 1–3 µm long and 0.4–0.7 µm wide.
• Shape: Straight rods, sometimes occurring singly or in pairs.
, • Cell Wall: Gram-negative, with a thin peptidoglycan layer and an outer membrane.
• Arrangement: Usually single; may form short chains.
• Motility: Most strains are motile with peritrichous flagella (flagella distributed all
around the cell).
• Capsule: Some strains possess a capsule (protective outer layer).
• Spores: Non-spore forming.
• Fimbriae (Pili): Present in many strains, helping in attachment to surfaces.
Classification of E. coli Pathotypes
Escherichia coli strains that cause disease are classified into. pathotypes based on their
virulence factors, mechanisms of infection, and clinical symptoms.
1. Enteropathogenic E. coli (EPEC)
• Causes infant diarrhea.
• Adheres to intestinal cells and disrupts microvilli.
2. Enterotoxigenic E. coli (ETEC)
• Common cause of traveler’s diarrhea.
• Produces heat-labile (LT) and heat-stable (ST) toxins.
3. Enterohemorrhagic E. coli (EHEC)
• Causes bloody diarrhea and hemorrhagic colitis.
• Produces Shiga toxin (e.g., O157:H7 strain).
4. Enteroinvasive E. coli (EIEC)
• Invades intestinal epithelial cells.
• Causes dysentery-like illness similar to Shigella.
5. Enteroaggregative E. coli (EAEC)
• Forms a “stacked-brick” pattern on intestinal mucosa.
• Causes persistent diarrhea, especially in children.
6. Diffusely Adherent E. coli (DAEC)
• Shows diffuse adherence to epithelial cells.
• Associated with mild diarrhea.
