Bacterial toxin, their classification, mode of action , bacteriocin and its typing

1. Santosh Yadav
BACTERIAL TOXINS AND
BACTERIOCIN
Santosh Yadav
M.Sc. Clinical Microbiology
Dept. of Microbiology
Institute of Medicine
Tribhuvan Univarsity Teaching Hospital, Nepal
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2. Santosh Yadav
Toxins
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 Are virulence factor of most of bacteria and one of
the major cause of tissue damage.
 Two types :- endotoxin and exotoxin.

3. Santosh Yadav
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Exotoxin Endotoxin
Secreted outside cell by both
Gram positive and Gram
negative bacteria
Relesed after lysis of Gram
negative cellwall
Protein Lipopolysaccharide
Heat labile (except- enterotoxin
of S.aureus )
Heat stable ( upto 250⁰c)
Highly antigenic Less antigenic
Highly toxic in minute dose (
microgram is fatal to animals)
Moderately toxic
Filterable not so(obtained only by cell
lysis )
Can be converted to toxoid cannot
Often enzymatic action no
Properties of bacterial toxin

4. Santosh Yadav
Endotoxin
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 LPS of Gram negative cell
has three parts:- O-
antigen , core
polysaccharide and
lipid A.
 Released usually when the
cell is lysed but can also be
released during vegetative
growth.
 Has same chemical
composition in almost all
bacteria and has same
toxic effect ( no matter
which bacteria produce it).
 Encoded by chromosomal
gene.

5. Santosh Yadav
Mode of action
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Endotoxin
( lipid A)
Activates
macrophages
IL-1/IL-6(fever)
TNF(fever and
hypotension) i
NO
(hypotension)
Activates
complement
C3a
(hypotension ,
edema)
C5a
(neutrophil
chemotaxis)
Activates
tissue factor
Coagulation
cascade ( DIC)

6. Santosh Yadav
Exotoxin
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 Are most powerful and active in small quantities.
 Either secreted by organism or leak into the
surrounding fluid after lysis of bacterial cell.
 Gene for exotoxin may be present on
chromosome or plasmid or bacteriophage
DNA.

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8. Santosh Yadav
A-B toxin
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 Have two components (A
and B)
 B components binds to
specific cell receptor and
facilitate the internalization
of A.
 Component A is active
(toxic) component.

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Superantigen
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Contd…
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 Some bacteria directly
inject exotoxin into
target cell via needle
like projections called
injectosome.
 Also called type III
secretory system.
 Bacteria having type III
secretory system are
more virulent.
Fig:- Injectosome

11. Santosh Yadav
BACTERIOCIN
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12. Santosh Yadav
BACTERIOCIN
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 Produced by many bacteria, protein in nature and
have bactericidal activity.
 Have killing action on strains of same or closely
related species.
 First reported by Gratia in 1925, Escherichia coli
producing a substances which is active against other
strains of the same species.
 Colicin – Gratia and Frederique in 1946.
 Bacteriocin- Jacob and Woolman in 1953.

13. Santosh Yadav
contd…
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 Are named on the basis of their bacterial species of
origin . Some of them are
i) Colicins are bacteriocins of E.coli,
ii) Aeruginocin of P. aeruginosa,
iii) Diphthericins - C. diphtheriae
iv) Cloacin of Enterobacter cloaceae,
v) Pesticin of Y. pestis,
vi) Monocin of Listeria monocytogenes,
vii) Cerecin of Bacillus cereus
viii) Staphylococcin of Staphylococcus aureus,
ix) Warnerin of et S. warneri

14. Santosh Yadav
contd…
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 Target cells have specific receptor for
attachment of bacteriocin( same as
bacterophage)
 Bacteria producing bacteriocin also carry
gene for immunity to them on chromosome or
plasmid.
 Many have narrow inhibitory spectrum of
activity ( but some have activity on broad
class of bacteria)
 Are plasmid or chromosomal mediated.

15. Santosh Yadav
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Gram negative bacteriocin

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Gram positive bacteriocin
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Mode of action
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Importance
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 Bacteriocins produced by non-pathogenic
bacteria kills other pathogenic
bacteria(Normal flora vs. Pathogens).
 Bacteriocins have also been suggested for
certain cancer treatment.
 Used for food presrvation in food industry (
eg..nisin produced by Lactococcus lactis is
active against many food spoiling bacteria)
 Used for bacteriocin typing of clinical strains
to aid in their identification and
characterization.

19. Santosh Yadav
Bacteriocin typing
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 Done for identification of isolated strains : as they
are same or different.
 A strain may be typed by:
1) Activity of their bacteriocin against a set of indicator
strains of same or closely related species, or
2) Pattern of their susceptibility to the bacteriocin of a
set of indicator strains.
 If the isolates are same strains, their bacteriocin
production and susceptibility patterns will be
identical.

20. Santosh Yadav
Pyocin typing
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Gillies and Govan(1966)- cross streaking
method
- The test strains are inoculated across the
surface of BHI agar plates.
- After overnight incubation at 37ᴼC , culture is
exposed to chloroform to kill the test strains and
then the test (producing) strains are scrapped-
off from the plate by using slide.
- The sensitive strains (Indicator strains) are
cross-streaked at right angle to the test strains.
- Incubated at 37ᴼC for 24 hours.
- Observed for inhibition of growth at each side of
the producing strain.

21. Santosh Yadav
Contd…
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 In pyocin typing technique with cross streaking
method, 105 main types and 25 subtypes can be
identified on the basis of pyocin production by
test strains using 13 indicators(1 to 8 and A to E).
Disadvantages of streak method
 To remove test strains growth before application
of indicator strain.
 Not reliable for mucoid colony of P. aeruginosa.
 48 hour period is needed to obtain result.

22. Santosh Yadav
Bibiliography
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 Microbiology : A Human Perspective by
Anderson and Nester
 Topley and Wilsons Microbiology and Microbial
infections, vol. 2
 A Handbook of Clinical Microbiology ; Prof. Dr.
Bharat Mani Pokhrel
 Microbiology by Tortora
 Ananthanarayan and Paniker Text Book Of
Microbiology
 Brock Biology of Microorganisms; Medigan and
Martinko.
 Microbiology ; Lansing M. Prescott.

23. Santosh Yadav
THANK YOU
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