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Created page with 'The cause and effect relationship between bacteria and infection is summarised by '''Koch's postulates''': *First postulate: Bacteria must be associated with the lesion **However…'
The cause and effect relationship between bacteria and infection is summarised by '''Koch's postulates''':
*First postulate: Bacteria must be associated with the lesion
**However some bacteria are known to colonise without causing symptoms
*Second postulate: Bacteria must be isolated in pure culture
**However some bacteria cannot be cultured
*Third postulate: Isolated bacteria must produce disease when innoculated into human or animal
*Fourth postulate: Bacteria must be reisolated from intentionally infected animal/human
Bacteria invasion can be either:
*'''Localised'''- e.g. an abscess
*'''Systemic'''-e.g. septicemia
The toxins produced by some bacteria can be classed as:
*'''Endotoxins'''- bacterial cell degradation products, e.g. LPS
*'''Exotoxins'''- toxic bacterial proteins, found in both Gram-negative and Gram-positive
Endotoxin pathology
*The endotoxin being referred to is LPS, found on Gram-negative bacteria
*Similar toxins found on Gram-positive bacteria include TSST-1, found on ''S. aureus''
*Effects of LPS are mainly due to excessive cytokine secretion- TNF-alpha, IL-1 and IL-2
*Primarily affects vascular system- sudden drop in blood pressure known as 'endotoxin shock', also 'septic' shock
*Also targets complement system- massive activation by the alternative pathway leads to inflammation and damage to small blood vessels
**Leakage of fluid into the alveoli leads to a condition known as adult respiratory distress syndrome (ARDS)
*The neurotoxicity attributed to the whooping-cough vaccine is thought to be due to an endotoxin on the ''B. pertussis'' bacterium
Types of exotoxin:
*Type 1- bind to target cell surface, excretion mediated by specialised pore-spanning proteins, e.g. superantigens
*Type 2- destroy integrity of membrane of eukaryotic cells, secretion mediated by Sec-dependent apparatus, e.g. phospholipases
*Type 3- one portion binds to host cell surface receptor, other acts on cell target, e.g. botulinum toxin
Toxins in disease:
*Diphtheria toxin- type 3 toxin, produced by ''C. diphtheriae'', causes damage to major organs
*Botulinum toxin- type 3 toxin, produced by ''C. botulinum'', affects control of nerve transmission
*Tetanus toxin- - type 3 toxin, produced by ''C. tetani'', affects nerve transmission
*Alpha toxin- type 2 toxin, produced by ''C. perfringens'', contributes to gangrene
*PMT- produced by ''P. multocida'', causes bone and weight loss
*Ciliary toxin- produced by ''B. pertussis'', inhibits cilia in bronchi
Although the reason why bacteria secrete such toxic compounds is unclear, many are of potential benefit to the microbe:
*Hyaluronidase: produced by ''Streptococcus'', this enzyme allows passage through the tissues
*Enterotoxins: such as those produced by ''Staphylococcus'' and Cholera, these cause diarrhoea and subsequent spread
*''E. histolytica'' toxin allows it to penetrate the gut wall[[Category:Bacteria]]
*First postulate: Bacteria must be associated with the lesion
**However some bacteria are known to colonise without causing symptoms
*Second postulate: Bacteria must be isolated in pure culture
**However some bacteria cannot be cultured
*Third postulate: Isolated bacteria must produce disease when innoculated into human or animal
*Fourth postulate: Bacteria must be reisolated from intentionally infected animal/human
Bacteria invasion can be either:
*'''Localised'''- e.g. an abscess
*'''Systemic'''-e.g. septicemia
The toxins produced by some bacteria can be classed as:
*'''Endotoxins'''- bacterial cell degradation products, e.g. LPS
*'''Exotoxins'''- toxic bacterial proteins, found in both Gram-negative and Gram-positive
Endotoxin pathology
*The endotoxin being referred to is LPS, found on Gram-negative bacteria
*Similar toxins found on Gram-positive bacteria include TSST-1, found on ''S. aureus''
*Effects of LPS are mainly due to excessive cytokine secretion- TNF-alpha, IL-1 and IL-2
*Primarily affects vascular system- sudden drop in blood pressure known as 'endotoxin shock', also 'septic' shock
*Also targets complement system- massive activation by the alternative pathway leads to inflammation and damage to small blood vessels
**Leakage of fluid into the alveoli leads to a condition known as adult respiratory distress syndrome (ARDS)
*The neurotoxicity attributed to the whooping-cough vaccine is thought to be due to an endotoxin on the ''B. pertussis'' bacterium
Types of exotoxin:
*Type 1- bind to target cell surface, excretion mediated by specialised pore-spanning proteins, e.g. superantigens
*Type 2- destroy integrity of membrane of eukaryotic cells, secretion mediated by Sec-dependent apparatus, e.g. phospholipases
*Type 3- one portion binds to host cell surface receptor, other acts on cell target, e.g. botulinum toxin
Toxins in disease:
*Diphtheria toxin- type 3 toxin, produced by ''C. diphtheriae'', causes damage to major organs
*Botulinum toxin- type 3 toxin, produced by ''C. botulinum'', affects control of nerve transmission
*Tetanus toxin- - type 3 toxin, produced by ''C. tetani'', affects nerve transmission
*Alpha toxin- type 2 toxin, produced by ''C. perfringens'', contributes to gangrene
*PMT- produced by ''P. multocida'', causes bone and weight loss
*Ciliary toxin- produced by ''B. pertussis'', inhibits cilia in bronchi
Although the reason why bacteria secrete such toxic compounds is unclear, many are of potential benefit to the microbe:
*Hyaluronidase: produced by ''Streptococcus'', this enzyme allows passage through the tissues
*Enterotoxins: such as those produced by ''Staphylococcus'' and Cholera, these cause diarrhoea and subsequent spread
*''E. histolytica'' toxin allows it to penetrate the gut wall[[Category:Bacteria]]