《微生物学》课程PPT课件讲稿（英文版）Lecture 9 Bacterial Toxins

Bacterial Toxins General aspects Definition Soluble substances that alter normal metabolism of host cells with deleterious effects on the host ● Host range Known for bacteria, but possible that they play a role in diseases caused by fungi, protozoa, and worms BIOL 533 Lecture 9

BIOL 533 2 Lecture 9 Bacterial Toxins: General Aspects • Definition – Soluble substances that alter normal metabolism of host cells with deleterious effects on the host • Host range – Known for bacteria, but possible that they play a role in diseases caused by fungi, protozoa, and worms

Bacterial Toxins General aspects ToXin type Exotoxin--protein produced by bacteria either excreted or bound to bacterial surface and released when lysed Endotoxin-lps of the outer membrane of Gram bacteria Acts as toxin only under special circumstances BIOL 533 Lecture 9

BIOL 533 3 Lecture 9 Bacterial Toxins: General Aspects • Toxin type – Exotoxin—protein produced by bacteria either excreted or bound to bacterial surface and released when lysed – Endotoxin—lps of the outer membrane of Gram— bacteria • Acts as toxin only under special circumstances

Bacterial Toxins General aspects Specificity Some act on certain cell types Other affect wide range of cells and tissues Numbers produced by single bacterium Some produce none ● Pneumococci BIOL 533 Lecture 9

BIOL 533 4 Lecture 9 Bacterial Toxins: General Aspects • Specificity – Some act on certain cell types – Other affect wide range of cells and tissues • Numbers produced by single bacterium – Some produce none • Pneumococci

Is Toxin Important in Infection? Questions to ask: Is virulence quantitatively correlated with toxin production? Does the purified toxin produce damage Can a specific antibody(antitoxin) prevent or alleviate the manifestations of the disease? If toxin production is impaired by a mutation is the disease process affected? BIOL 533 Lecture 9

BIOL 533 5 Lecture 9 Is Toxin Important in Infection? • Questions to ask: – Is virulence quantitatively correlated with toxin production? – Does the purified toxin produce damage? – Can a specific antibody (antitoxin) prevent or alleviate the manifestations of the disease? – If toxin production is impaired by a mutation, is the disease process affected?

E If So, What are Toxin Properties?y Questions to ask: What is the mechanism of action? Why is it specific for certain cells or tissues? Does the pathogen make other toxins, and if sO, do they interact with one another? Some make none: pneumococci Some make only one: agents that cause cholera, diphtheria tetanus and botulism Other make many: staphylococci, streptococci BIOL 533 Lecture 9

BIOL 533 6 Lecture 9 If So, What are Toxin Properties? • Questions to ask: – What is the mechanism of action? – Why is it specific for certain cells or tissues? – Does the pathogen make other toxins, and if so, do they interact with one another? • Some make none: pneumococci • Some make only one: agents that cause cholera, diphtheria, tetanus, and botulism • Other make many: staphylococci, streptococci

Toxin production Properties Dispensable, but essential under certain situations where survival and spread are at stake Genes frequently carried on plasmids and temperate bacteriophage BIOL 533 7 Lecture 9

BIOL 533 7 Lecture 9 Toxin Production • Properties – Dispensable, but essential under certain situations where survival and spread are at stake – Genes frequently carried on plasmids and temperate bacteriophage

Toxin production Found on phage; toxin genes for Diphtheria o Botulism o Scarlet fever Toxic streptococci (flesh-eating") Found on plasmids E coli toxin causes diarrhea S aureus toxin causes"scalded skin syndrome E,CO0157:H7 BIOL 533 Lecture 9

BIOL 533 8 Lecture 9 Toxin Production – Found on phage; toxin genes for: • Diphtheria • Botulism • Scarlet fever • Toxic streptococci (“flesh-eating”) – Found on plasmids: • E. coli toxin causes diarrhea • S. aureus toxin causes “scalded skin syndrome” • E. coli 0157:H7

Toxin production Properties Mobile elements ensure that genes can be spread to nontoxigenic derivatives or be lost from cell Experimentally called"curing"get nontoxigenic derivatives Phase of production Some produced continuously by growing bacteria Other synthesized when cells enter stationary phase(true also for many antibiotics) BIOL 533 Lecture 9

BIOL 533 9 Lecture 9 Toxin Production – Properties • Mobile elements ensure that genes can be spread to nontoxigenic derivatives or be lost from cell – Experimentally called “curing”—get nontoxigenic derivatives – Phase of production • Some produced continuously by growing bacteria • Other synthesized when cells enter stationary phase (true also for many antibiotics)

Toxin production Explanation Certain toxins may help bacteria get scarce nutrients Example: high levels of diphtheria toxin produced when cell depleted of iron Very little free iron in normal tissue Is this a way for organisms to obtain it from dead tissue? BIOL 533 Lecture 9

BIOL 533 10 Lecture 9 Toxin Production – Explanation • Certain toxins may help bacteria get scarce nutrients • Example: high levels of diphtheria toxin produced when cell depleted of iron – Very little free iron in normal tissue – Is this a way for organisms to obtain it from dead tissue?

Toxin production Sporulating bacteria sometimes release toxins during spore formation Bacterial cells eventually lyse and liberate cytoplasmic proteins, including toxins Examples: organisms that cause botulism, gas gangrene, or tetanus In contaminated wound some organisms are growing and some are sporulating End result is continual production BIOL 533 Lecture 9

BIOL 533 11 Lecture 9 Toxin Production – Sporulating bacteria sometimes release toxins during spore formation • Bacterial cells eventually lyse and liberate cytoplasmic proteins, including toxins – Examples: organisms that cause botulism, gas gangrene, or tetanus • In contaminated wound, some organisms are growing and some are sporulating – End result is continual production