Bacteria

1. E.coli

2. INTRODUCTION
 It is a Gram-negative, facultative
anaerobic, rod-shaped, coliform
bacterium of the genus Escherichia that
is commonly found in the lower intestine
of warm-blooded organisms
(endotherms).

3. Scientific
Classification
 Domain: Bacteria
 Phylum: Proteobacteria
 Class: Gammaproteobacteria
 Order: Enterobacterales
 Family: Enterobacteriaceae
 Genus: Escherichia
 Species: E. coli

4. Type and
Morphology
 Facultative anaerobe
 Nonsporulating bacterium.
 Cells are typically rod-shaped, and are about 2.0
μm long and 0.25–1.0 μm in diameter
 Strains that possess flagella are motile.
 The flagella have a peritrichous arrangement

5. Cultural
characters
 Grows between 10 – 40 c optimal at 37 c
 Produce Large grayish ,Thick white ,
moist smooth opaque colonies
 May contain capsule.
 On MacConkey medium Produce Bright
pink Lactose fermenters

6. PhylogenyofE.
colistrains
 The species is divided into seven groups
 Based on whole genome sequencing analysis

7. Serotypes
Classification
 Based on surface antigens
 O antigen: part of lipopolysaccharide layer;
 H: flagellin;
 K antigen: capsule

8. Genome
 The first complete DNA sequence of an E. coli genome
was published in 1997.
 It is a circular DNA molecule 4.6 million base pairs in
length, containing
 4288 annotated protein-coding genes (organized into
2584 operons),
 Seven ribosomal RNA (rRNA) operons, and
 86 transfer RNA (tRNA) genes.
 The genome was observed to contain a significant
number of transposable genetic elements, repeat
elements, cryptic prophages, and bacteriophage
remnants

9. Virulence
Factors
 Two types of virulence factors in E.coli
 Surface antigens and Toxins
 The somatic lipopolysaccharide surface O antigen has
endotoxic activity and protects from phagocytosis and
bactericidal effects

10. Fimbriae
 Fimbriae also promote virulence
 • Present in large numbers causing mannose sensitive
Haemagglutination
 •

11. Toxins
 Important toxins produces two types of toxins
 Enterotoxin
 Hemolysin

12. Enterotoxin
 produced by enterotoxigenic strains of E. coli
(ETEC).
 Causes a movement of water and ions from
the tissues to the bowel resulting in watery
diarrhea.
 There are two types of enterotoxin:
 Heat Liable HL
 Heat Stable

13. Enterotoxin
Structure
 Both enterotoxins are composed of five beta subunits
(for binding) and 1 alpha subunit (has the toxic
enzymatic activity)

14. HeatLiable
Toxins
 HL – is heat labile and binds to
specific Gm1 gangliosides on the
epithelial cells of the small intestine
where it ADP-ribosylates Gs which
stimulates adenylate cyclase to
increase production of cAMP.
 Increased cAMP alters the activity of
sodium and chloride transporters
producing an ion imbalance that
results in fluid transport into the
bowel.

15. HeatLiable
Toxins
 Labile toxin 1956 De experiments in Rabbit ileal loop
causes outpouring of fluids
 E.coli Labile toxin like Cholera toxin
 HL contains component A and B
 A = Active
 B= Binding
 B causes Binding with Gm I Ganglioside receptor on
Intestinal epithelial cells

16. HeatLiable
Toxins
 Component A Activated to A1 and A2
 A1 Activates adenyl cyclase in the enterocytes to form
cyclic adenosine 5 monophosphate
 Causes to increase outflow of water and electrolytes
in the gut lumen causes Diarrhea

17. HeatStable
Toxins
 ST A and ST B
 ST A Acts by activation of Cyclic guano sine
monophosphate.( C GMP )
 Causes fluid accumulation in Intestine.

18. Hemolysin
 Alpha-hemolysin (Hly A) is a common exotoxin
produced by Escherichia coli
 IT is responsible for the zone of β-hemolysis surrounding
bacterial colonies on blood agar.
 It causes hemolysis by forming pores in the erythrocyte
membrane

19. E.coliinfections
 Neonatal meningitis – is the leading cause of neonatal
meningitis and septicemia with a high mortality rate.
 Usually caused by strains with the K1 capsular
antigen.
 Gastroenteritis – there are several distinct types of E.
coli that are involved in different types of
gastroenteritis:
 enterotoxigenic E. coli (ETEC),
 enteroinvasive E. coli (EIEC),
 enteropathogenic E. coli (EPEC) ,
 enteroaggregative E. coli (EAEC), and
 enterohemorrhagic E. coli (EHEC).

20. Enterotoxigenic E. coli (ETEC) adheres to the
small bowel mucosa and delivers secretory
enterotoxins. Enterohemorrhagic E.
coli (EHEC) adheres intimately to the colonic
mucosa (“attaching and effacting”) and
transduces a signal, resulting in secretory
diarrhea. Concurrently, the organism releases
shiga toxin, resulting in local and systemic
effects. Enteroaggregative E. coli (EAEC)
adheres in a thick mucous gel and causes
intestinal secretion and damage. Diffusely
adherent E. coli (DAEC) has been shown to
elicit elongation of microvilli in vitro, although
this effect has not been demonstrated in vivo.
Enteropathogenic E. coli (EPEC) elicits the
attaching and effacing lesion in the small
bowel, resulting in intestinal secretion.
Enteroinvasive E. coli (EIEC) invades the
colonic mucosa, giving rise to an inflammatory