Santosh Yadav

BACTERIAL TOXINS AND BACTERIOCIN

Santosh Yadav M.Sc. Clinical Microbiology

Dept. of MicrobiologyInstitute of Medicine

Tribhuvan Univarsity Teaching Hospital, Nepal

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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.

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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 LipopolysaccharideHeat 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

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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.

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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 complementC3a (hypotension , edema)

C5a (neutrophil chemotaxis)

Activates tissue factorCoagulation cascade ( DIC)

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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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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

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BACTERIOCIN

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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.

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contd…

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Are named on the basis of their bacterial

species of origin . Some of them arei) Colicins are bacteriocins of E.coli, ii) Aeruginocin of P. aeruginosa, iii) Diphthericins - C. diphtheriaeiv) Cloacin of Enterobacter cloaceae, v) Pesticin of Y. pestis, vi) Monocin of Listeria monocytogenes, vii) Cerecin of Bacillus cereusviii) Staphylococcin of Staphylococcus aureus,ix) Warnerin of et S. warneri

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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.

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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.

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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.

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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.

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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 methodTo 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.

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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 TortoraAnanthanarayan and Paniker Text Book Of

MicrobiologyBrock Biology of Microorganisms; Medigan and

Martinko.Microbiology ; Lansing M. Prescott.Medical bacteriology ; N.C. Dey.

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THANK YOU

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