Escherichia coli (E. coli) is a common bacterium found in the intestines that can cause illness when it enters other parts of the body. Certain pathogenic strains produce virulence factors like toxins and surface antigens that allow it to cause infections. E. coli is the most common cause of urinary tract infections and can lead to diarrhea through the action of different enterotoxins. Diagnosis involves culturing samples from sites of infection to identify E. coli and test for antibiotic susceptibility. Treatment depends on the antimicrobial susceptibility results and may include antibiotics like aminocillins, cephalosporins, or carbapenems.

1. Escherichia Coli
J.JOSEPH SAMRAJ
U21MB345 (89)

2. Objectives
● Introduction
● Etiology
● Virulence factors
● Properties of enterotoxins of E. coli
● Clinical manifestation
● Laboratory diagnosis
● Treatment

3. Introduction
Escherichia coli (E. coli) is a Gram-negative, facultative anaerobic, rod-shaped
bacterium that is commonly found in the lower intestine of warm-blooded
organisms. However, some strains of E. coli can cause disease, when it enters
other system. These pathogenic strains can be found in contaminated food, water,
or soil.

4. Etiology
● Escherichia coli is the most important species encountered as a human
pathogen. It is also the most common aerobe to be harbored in the gut of
humans and animals.
● After being excreted in feces, E. coli remains viable only for some days in the
environment. This means that detection of E. coli, especially a variant called
thermotolerant E. coli (which survives at 44°C), can be used as an indicator of
recent contamination of drinking water with human or animal feces.
● Other species of E. coli are less important as human pathogens. These include
● E. fergusonii
● E. hermannii
● E. vulneris….
which are rarely isolated from clinical specimens.

5. Virulence factors
Virulence factors of E. coli is grouped into surface antigens & toxins
● SURFACE ANTIGENS
Somatic or O Antigen:
● Present on lipo-polysaccharide (LPS) antigen.
● Major surface antigen inducing antibody formation.
Flagellar or H Antigen:
● Responsible for bacterial motility and virulence.
Capsular or K Antigen:
● Polysaccharide capsular antigen on the envelope.
● Expressed by strains causing neonatal meningitis, pyelonephritis, and septicemia.
Fimbrial Antigen (Pilus):
● Organ of adhesion, aiding in attachment and colonization.
● Various types include CFA, Mannose resistant fimbriae, and P fimbriae.

6. ● Toxins
Enterotoxins:
● Produced by diarrheagenic E. coli strains.
● Three types: heat-labile toxin, heat-stable toxin, and verocytotoxin.
Cytotoxic Necrotizing Factor 1 (CNF1) and Secreted Autotransporter Toxin (SAT):
● Cytotoxic to bladder and kidney cells.
● Act as virulence factors for urinary tract infections (UTIs).

7. Properties of enterotoxins of E. Coli
Type:
There are three main types of enterotoxins produced by E. coli: heat-labile (LT), heat-stable (ST) and
verocytotoxin (shiga toxin)
Mode of action:
● Heat-labile enterotoxin (LT):
LT is a large protein that is encoded by a bacteriophage. LT is a potent toxin, and can cause
diarrhea within hours of ingestion.
● Heat-stable enterotoxin (ST):
ST is a smaller protein that is encoded by the bacterium's chromosome. ST toxins are less potent
than LT, and can take several days to cause diarrhea.
● Verocytotoxin works by inhibiting protein synthesis in cells. This prevents the cell from making new
proteins, which eventually leads to cell death.

8. Clinical manifestation
Urinary tract infection (UTI): E. coli is the most common cause of UTI, accounting for 70-75% of all
cases.
Diarrhea: E. coli can cause six different types of diarrhea, including:
● Enteropathogenic E. coli (EPEC)
● Enterotoxigenic E. coli (ETEC)
● Enteroinvasive E. coli (EIEC)
● Enterohemorrhagic E. coli (EHEC)
● Enteroaggregative E. coli (EAEC)
● Diffusely adherent E. coli (DAEC)
Other infections: E. coli can also cause a variety of other infections, including:
● Abdominal infections, such as primary bacterial peritonitis and secondary bacterial peritonitis
● Pneumonia
● Meningitis
● Wound and soft tissue infections
● Bacterial prostatitis

9. Enteropathogenic E. coli
(EPEC)
Causes intestinal infections and is known for attaching
to the intestinal lining, leading to diarrhea, especially in
infants and young children.
Enterotoxigenic E. coli (ETEC) Produces toxins that cause traveler's diarrhea and other
gastrointestinal illnesses, often associated with
contaminated food and water.
Enteroinvasive E. coli (EIEC) Invades the intestinal lining, causing inflammation and
symptoms similar to those of Shigella, including
dysentery and fever.
Enterohemorrhagic E. coli
(EHEC)
Produces toxins that can lead to severe foodborne
illnesses, including bloody diarrhea and, in some cases,
kidney failure (hemolytic uremic syndrome).
Enteroaggregative E. coli
(EAEC)
Forms clumps on the intestinal lining, leading to
persistent diarrhea, especially in young children and
immunocompromised individuals.
Diffusely adherent E. coli
(DAEC)
Causes diarrhea and adheres to the intestinal lining
diffusely, without forming clumps.

10. Laboratory diagnosis
● Sample collection: The sample to be collected depends on the site of infection. For
example, urine, stool, pus, wound swab, blood, or cerebrospinal fluid (CSF) may be
collected.
● Direct smear: A Gram stain of the sample is performed to visualize the bacteria. E.
coli is a gram-negative rod. Pus cells may also be seen in the smear.
● Culture: The sample is cultured on blood agar and MacConkey agar. On blood agar, E.
coli colonies appear gray and moist. On MacConkey agar, E. coli colonies appear flat
and pink.
● Culture smear and motility: A Gram stain of the culture is performed to confirm the
identification of E. coli. E. coli is a motile gram-negative rod.
● Antimicrobial susceptibility testing: Antimicrobial susceptibility testing is performed
to determine which antibiotics are effective against E. coli.

12. Treatment
● Treatment for hospital-acquired multidrug-resistant E. coli (MDR E. coli) infections
is based on the antimicrobial susceptibility test report.
● If the E. coli is susceptible to aminocillins, third-generation cephalosporins,
quinolones, or cotrimoxazole, then these agents may be preferred.
● Carbapenems, amikacin, or β-lactam/β-lactamase inhibitor combinations (BL/BLIS)
are usually the agent of choice for hospital-acquired MDR E. coli infections.
● Polymyxins, fosfomycin, or tigecycline are the next line antimicrobials for
carbapenem-resistant isolates.
● In healthcare facilities with high prevalence of MDR E. coli, empirical treatment
should be started with higher spectrum antimicrobial such as carbapenem.
Reference:
Apurba S Sastry, Sandhya Bhat Essential of Medical Microbiology. 4th ed

13. Thank you