Eschericia coli (E. coli) is a rod-shaped bacterium commonly found in the intestines of warm-blooded organisms. E. coli strains are classified based on serological characteristics and virulence properties including enterotoxigenic E. coli, enteropathogenic E. coli, enteroinvasive E. coli, enterohemorrhagic E. coli, and enteroaggregative E. coli. On MacConkey agar, E. coli forms red or pink lactose-positive colonies due to acid production from lactose fermentation. On blood agar, E. coli colonies show no hemolysis but some pathogenic strains are beta-hemolytic, appearing smooth and gray, around

1. ESCHERICHIA COLI
BIOCHEMISTRY

2. INTRODUCTION
• ESCHERICHIA COLI (COMMONLY ABBREVIATED E. COLI) IS A GRAM-NEGATIVE, ROD-SHAPED
BACTERIUM THAT IS COMMONLY FOUND IN THE LOWER INTESTINE OF WARM-BLOODED
ORGANISMS.
• ENTERIC E. COLI (EC) ARE CLASSIFIED ON THE BASIS OF SEROLOGICAL CHARACTERISTICS AND
VIRULENCE PROPERTIES:
• ENTEROTOXIGENIC E. COLI (ETEC)
• ENTEROPATHOGENIC E. COLI (EPEC)
• ENTEROINVASIVE E. COLI (EIEC)
• ENTEROHEMORRHAGIC E. COLI (EHEC)
• ENTEROAGGREGATIVE E. COLI (EAEC)

3. MACCONKEY AGAR
• RED/PINK LACTOSE-POSITIVE COLONIES.
• LACTOSE IF FERMENTED RESULTING IN PRODUCTION OF ACID; THIS ACID CHANGES THE COLOR OF
INDICATOR FROM NEUTRAL RED TO PINK.
• COLONIES PRODUCED ARE PINK TO RED, FLAT, DRY, & 2-3MM IN DIAMETER.

4. BLOOD AGAR
• COLONIES ARE WITHOUT HEMOLYSIS (GAMMA_HEMOLYSIS), BUT MANY STRAINS
ISOLATED FROM INFECTIONS SHOW BETA-HEMOLYTIC.
• COLONIES ARE SMOOTH, DULL GRAY, & 2-3MM IN DIAMETER.

5. EXTRA POINTS
• IT MOSTLY INVADES THE GASTROINTESTINAL SYSTEM (SPECIFICALLY THE
COLON) AND URINARY TRACT.