Adherence of bacteria Vibrio holerae on the surface of enterocytes Gonococci on the surface of urinary epithelium
Action of enzymes Exoenzymes dissolve extracellular barrier and make possible penetration of bacteria through or between cells to underlying tissues Collagenase and hyaluronidase , which degrade collagen and hyaluronic acid, respectively, thereby allowing the bacteria to spread through subcutaneous tissue.
Pathogenic enzymes Dissolves blood clots Fibrinolysin Destroys red blood cells and other tissue cells Lecithinase Breaks down DNA Deoxyribonuclease Breaks down fat Lipase Breaks down hyaluronic acid, a tissue component Hyaluronidase (spreading factor) Breaks down collagen (connective tissue fiber) Collagenase Coagulates plasma; blood clots Coagulase Breaks down lecithin, a lipid component of mammalian cell membrane Phospholipase Function Enzyme
Action of toxins Exotoxins diffuse to target cells, which are poisoned and disrupted
Differential characteristics of bacterial exotoxins and endotoxins (1) Stable at 100 0 C for 1 hour Destroyed rapidly at 60 0 C Heat stability Bacterial chromosome Bacterial chromosome, plasmid or bacteriophage Location of genes Lipopilysaccharide (LPS) Polypeptide Chemical Released by cell during lysis Secreted from live cell Manner of release Most of gram-negative bacteria A few gram-positive and gram-negative bacteria Source Endotoxin Exotoxin Property
Differential characteristics of bacterial exotoxins and endotoxins (2) Low (toxic in high dose) High (toxic in minute amounts) Toxicity Systemic: fever, inflammation Specific to a cell type Clinical effects Do not convert to toxoid Convert to toxoid that used as vaccines Toxoid formation Low. Poorly antigenic High. Induces high titer antibodies called antitoxins Antigenicity Yes Usually not Fever stimulation Endotoxin Exotoxin Property
Classification of exotoxins based on mechanism of action Staphylococcus aureus Cytotoxin that causes the lysis of human erythrocytes and some other cells. Hemolysin Corynebacte-rium diphtheriae Causes cell death, often by lysis and/or interference with protein synthesis Cytotoxin Vibrio cholerae Inflammation of the gastrointestinal tract; typically causes excessive secretions of fluid and electrolytes from the lining of the gastrointestinal tract Enterotoxin Clostridium botulinum Interference with nerve transmission Neurotoxin Bacterium-producer General site and mode of action Type of toxin
Effects of endotoxin Activation of Hageman factor Coagulation Alternative pathway of complement (C3a,C5a) Inflammation Bradykinin, nitric oxide Hypotension (shock) Interleukin-1 Fever Mediator or mechanism Clinical findings