Escherichia coli (E. coli) is a rod-shaped, facultatively anaerobic, Gram-negative bacterium commonly found in the intestines of humans and animals. E. coli can be either commensal or pathogenic. Pathogenic types include enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC), enterohemorrhagic E. coli (EHEC), enteroinvasive E. coli (EIEC), and enteroaggregative E. coli (EAEC) which cause diseases like diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome. E. coli is typically identified through culture and biochemical

1. Escherichia coli
(E. coli)
Prepared by
Prashant Dahal
BSc. Microbiology Final Year
Sunsari Technical College

2. TABLE OF CONTENT
Table of Contents
1. Introduction
2. Morphology
3. Serotypes
4. Cultural characters
5. Biochemistry
6. Clinical significances
a. Virulence factors
b. Pathotypes of E. coli
c. Pathogenesis
d. Disease causing
7. Diagnosis
8. Treatment
9. Positive roles
10. Summary & Sources

3. INTRODUCTION
• Gram-negative, Rod shaped, Facultative
anaerobic, non-sporing motile/non-motile
coliform bacteria of genus Escherichia in
Enterobacteriaceae family.
• Named after discoverer, German physician
:Theodor Escherich, in 1886
• Commensal / pathogenic; found in GIT of warm-
blodded, hence in Enteric bacteria
• One of the most studied bacetria

4. MORPHOLOGY
• Rod shaped, around 2 𝜇m (1–3) X 0.4–0.7 𝜇m in size, 0.7
cubic 𝜇m volume
• Peritrichous flagella, fimbriae/pilli presence
• Some contains, polysaccharide capsule
• Mostly singular form or in pair

5. Serotypes
Serotyping is based on 3 major
antigens:
• somatic lipopolysaccharide (LPS) (O),
heat stable, common to Enterobacteriaceae,
173 types
• flagellar (H) heat & alcohol labile, genus
specific proteins, 75 types
• capsular (K) heat-labile, acidic, 103 types
• Beside there is another antigenic
structure, fimbrial (F) : heat labile, 2
types(K88, K99)
SEROTYPES
• More than 200 serotypes
Eg: 1. E. coli O104:H4 (caused diarrhoeal outbreak in
Germany ,2011)
2. E. coli O157:H7 (STEC, diarrhoeal, UTI infection)
3. E. coli O121
4. E. coli O103, O128

6. CULTURE
• Aerobic / Facultative , pH: 7.2, Temp.: 10-49 with
optm.temp. 37, generation time 20 min
• Common specimens for clinical culture: Urine, Stool, Blood,
CSF, Aspirates
• Common media: MAC, CLED, NA, BA, CAP, TSA, EMB, VRBA,
m-Endo
MEDIA CHARACTERS
MAC circular, moist, smooth, non-mucoid, 2-3mm, convex , pink with darker
pink halo, (mucoid if capsulated)
CLED Opaque yellow colonies with a slightly deeper yellow center, circular,
moist, smooth, non-mucoid, 2mm, convex
BAP big, circular, 1-4mm, gray and moist, 𝛽-haemolytic
EMB Blue-black centered, green metallic sheen, circular, 2-3mm, convex,
smooth
NA large, 2-4mm, circular, low convex, grayish, white, moist, smooth, and
opaque
XLD Yellow, circular, large, flat

7. BIOCHEMICAL CHARACTERS
TEST RESULT
Gm.Stain -ve (Red/ pink) Rod
IMViC + + - -
TSI Acid / Acid (Y /Y )
Urease -ve
Catalase +ve
Oxidase -ve
Nitrate +ve
H2S -ve
Motility +ve (-ve absent flagella)

8. CLINICAL SIGNIFICANCE
VIRULENCE FACTORS BIOLOGICAL ROLE
Fimbriae Adherence of bacteria, mannose-resistant
hemagglutination
Adhesins firm adhesion, prevent flushing in GIT, GUT
Endotoxin manifestations of endotoxic shock, protect from
phagocytosis & bactericidal effects of complement
Capsule Protect from serum killing & phagocytosis
Hemolysins pathogenesis of disease caused by uropathogenic strains
(Enterotoxins )
1. Shiga toxins
2. Heat stable toxin
3. Heat labile toxin
Cytotoxins
Causes increased secretion of fluids
Watery diarrhea due to hypersecretion of fluid into the
lumen
Sequestration of growth
factors
Compete for nutrition in host cell
PATHO-TYPES
1. ETEC -- Enterotoxigenic E. coli
2. EPEC -- Enteropathogenic E. coli
3. EAEC -- Enteroaggregative E. coli
4. EIEC -- Enteroinvasive E. coli
5. EHEC -- Enterohemorrhagic E. coli
( STEC -- Shiga Toxin–Producing E. coli)
(VTEC -- Verocytotoxin-Producing E. coli)
6. DAEC -- Diffusely-adherent E. coli

9. PATHOGENESIS
EHEC (STEC, VTEC)
1. Epidemiology / Diesease: Hemorrhagic colitis and hemolytic
uremic syndrome in all ages and thrombotic
thrombocytopenic purpura in adults
2. Diarrhoea : Bloody or non-bloody
3. Mechanism: Cytotoxin production and adherence
4. caused by E.coli 0157:H7, E.coli O26:H11

10. EPEC
1. Epidemiology/Disease: Acute and chronic endemic and epidemic diarrhea
in infants
2. Diarrhoea: Watery
3. Mechanism: Adherence effacement, adhere to intestinal mucosa and
produce a characteristic lesion in the gastrointestinal tract via. plasmid
coded bundle-forming pill, which form cup-like projections called
pedestals.
4. Do not produce ENTEROTOXIN and NON - INVASIVE
5. Fecal-oral exposure
6. O44, O55, O86, O111, O114, O119, O125, O126, O127, O128, O142 and

11. EAEC
1. Epidemiology / Disease: Chronic diarrhea and growth retardation in infants
2. Diarrhoea: Watery
3. Mechanism: Adherence, "stacked brick" adherence pattern on HEP-2 or
HeLa cells.;
4. Gene encoding Adhesin and ST is variable
5. E. coli 0104: H4, produce ST

12. ETEC
1. Disease/ Epidemiology: Traveler’s Diarrhoea, & Infantile diarrhea in
developing countries
2. Diarrhoea: Watery
3. Mechanism: Adherence (mediated by fimbrial protein called CFA
(colorlization factor antigen)) , enterotoxin production (both heat-labile
and/or heat-stable enterotoxins.)
4. one of the most common causes of bacterial diarrheal disease in developing
countries (estimated 840 million cases annually)
5. (O6:H16, O8:H9 or O8:H-, O15:H11) E. coli-06, 08, 0 15, 025, 0 27, 0 153, 0
159

13. EIEC
1. Epidemiology / Disease: Diarrhea with fever in all ages,
2. Diarrhoea: Bloody or non-bloody
3. Mechanism: invade and destroy the colonic epithelium,
plasmid mediated Adherence & invasion of mucosa
4. rare in both developed and developing countries
5. Few serotypes; O28, O112, O115, O124, O136, O143, O144,
O147, O152, O164 and O167

14. DAEC
1. Epidemiology: Age dependent diarrhoea in Children (2-6 yr)
2. Diarrhoea: Watery
3. Mechanism: adherence by fimbriae
4. Less known

16. Disease caused
1. UTI (bacteriuria)
2. Gastroenteritis (Diarrhoea, ulcer)
3. Septicemia
4. Neonatal sepsis
5. Meningitis

17. Laboratory Diagnosis
A. Sample: Urine for UTI, Stool for gastroenteritis, Blood
for speticemia/sepsis, CSF for meningitidis
B. Microscopy
C. Culture & Biochemical tests
D. To separate PATHO-TYPES
1. Commercially available immunoassay (ETEC)
2. culture and adherence on Hep-2, HeLa cells (EPEC, EAEC)
3. ELISA, latex-agglitunation, SMAC culture (STEC)
4. Sereny test , HeLa (EIEC)
E. PCR and Gene coding for serotyping

18. A. E. coli O157:H7, non-sorbitol fermenter
B. Sorbitol fermenter bacteria

19. TREATMENT
• Generally, adult need none in diarrhoea
• UTI - antibacterial agents, including ampicillin,
cephalosporins, tetracyclines, quinolones,
aminoglycosides, trimethoprim and
sulphonamides
• Enteric E. coli: Fluid + ORS supplement,
antibiotics are used in severe cases
• Meningititis and sepsis: Compulsory
antibiotics
However there is a huge obstacle developing in
treatment of E. coli : ABR pathogenic strains of E. coli
WHO has listed ABR E. coli as pathogen of concern
Resistance is mainly by production of Beta-lactamases
ESBL, ABL, CBL are most commonly associated in
human infection

20. POSITIVE ROLES OF E. COLI
• Commensal of GIT, producing Vit.K and
preventing colonization of other enteric pathogens
like Cholera, Shigella, Pseudo.., Staph
• Production of Insulin commercially
• Tools of bio-technology in gene cloning and
transfer
• Used as probiotics
• Indicator organism of Water, milk and juices
contamination

21. SUMMARY
• Gm(-ve), rod, facultative, flagellate, most
studied
• Commensal in GIT of all vertebrates
• Occasionally cause disease
• Pathogens are classified as EIEC, EPEC, EAEC,
EHEC, ETEC, DAEC
• EMB, m-Endo selective media
• MAC, SMAC, CLED, BA – used in clinical
culture

22. REFERENCES
• Greenwood Medical Microbiology
• Textbook of Diagnostic Microbiology by Connie R Mahon, Donald C. Lehman &
George Mansuseli
• Textbook of Microbiology & Immunology by Subash Chandra Parija
• Escherichia coli (E. coli)- An Overview/ Microbenotes.com
• E. coli Pathotypes / Microbenotes.com
• Murray, P. R., Rosenthal, K. S., & Pfaller, M. A. (2013). Medical microbiology.
Philadelphia: Elsevier/Saunders
• Sastry A.S. & Bhat S.K. (2016). Essentials of Medical Microbiology. New Delhi :
Jaypee Brothers Medical Publishers.
• Wikipedia source

23. THANK YOU !!