1. PATHOGENIC EFFECTS OF BACTERIA
H.A. MWAKYOMA

2. PATHOGENIC EFFECTS OF BACTERIA
Extracellular bacteria
Intracellular bacteria
Extracellular bacteria:- examples
Staphylococcus aureus
Pneumococci
Gonococci (Neisseria gonorrhoea)
Clostridium
tetani
perfringence
botulinum

3. Extracellular bacteria:- examples :- examples
Salmonella sp
Vibrio cholerae
Shigella sp
Gram –negative bacteria
Klebsiella pneumoniae
E. coli
Pseudomonas sp. etc

4. Extracellular bacteria:-
Extracellular bacterial pathogens of man resist early engulfment (phagocytosis) by neutrophils in order to gain a foothold in the host tissue for effective mechanism to favour their survival (ability to resist phagocytosis)
Bacteria may resist phagocytosis in a number of ways:
Generation of toxins;
Some bacteria generate toxins lethal for leucocytes and their host cells

5. Bacteria may resist phagocytosis in a number of ways:
Forming slipperly hydrophilic capsules
Other bacteria solve their survival problem by forming slipperly hydrophilic antiphagocytic capsule- e.g. pneumococci that resist attachment to wondering neutrophils.
Some bacteria resist phagocytosis by the presence of M- protein and hyluronic acid- in Streptococci pyogens

6. FALCULTATIVE INTRACELLULAR BACTERIA- direct damage
Some organisms like Tubercle bacilli and other chronic infectious agents counteract phagocyte aggression after being interiorized by the following mechanisms:-
Inhibiting fusion of phagocytic vacuoles with lysosome
Shielding (Evading) themselves from the free radicals and enzymes generated around them, hence cannot leave the phagosome.
They have the potential of establishing latent foci of infection capable of long-term reactivation often resulting in granulomatous lesions
Bacterial survival in the face of effective phagolysosome fusion is attributed to specific surface components:-

7. TB mechanisms- cont-- Mycocydes
Covalently linked complex lipids and carbohydrates
Appear to be directly related to bacterial virulence
Sulfated glycolipids (sulfatide)
Prevents the fusion of phagosome with lysosome and favours the intracellular survival of Mycobacteria within macrophages
The lipid fraction contributes to virulence and to the sensitivity state associated with tuberculosis
The emergence of hypersensitivity reaction to the tubercle bacilli plays a dominant role in the tissue destruction encountered in this disease.

8. FALCULTATIVE INTRACELLULAR BACTERIA
Having established themselves, bacteria can damage host tissues directly or indirectly in a number of ways- mechanism of bacteria-induced injury. This can be done by;
Bacterial adhesins and
Toxins/ Enzymes(Aggressins)

9. BACTERIAL TOXINS Bacterial toxins are divided into;
Those that are liberated from multiplying bacteria (Exotoxins) and
Those that are associated with the cell wall and are released after death of the bacterium (Endotoxins)

10. EXOTOXINS
ACTIONS:
Bacterial exotoxins appear to work in two main ways:
In the form of cytolytic toxins which can alter cell permeability
As Bipartite toxins that bind to a receptor with one portion, allowing the release of the other portion into the host cytoplasm.

11. ACTIONS of EXOTOXINS
Bipartite exotoxins are actually activated by enzyme cleavage within the host target cell, e.g. diphtheria, cholera.

12. EXOTOXINS Most are produced by gram-positive bacteria
They are proteins
A few are specific enzymes (Aggressins)
When liberated locally they can cause local cell and tissue damage
Those that damage phagocytic cells are particularly useful to the microorganism
Those that promote the spread of bacteria enter the blood and cause generalized toxic effects

13. EXOTOXINS Clostridium perfringens: Clostridium perfrigens atoxin
Is a phosphalipase – acts on cell membrane
May cause;
Cell necrosis
Haemolysis
toxaemia

14. EXOTOXINS Clostridium tetani toxin:
Blocks the action of inhibitory neurones
Causes;
Overaction of motor neurons
Muscle spasms
Lockjaw

15. EXOTOXINS Corynebacterium diphtheriae toxin:
Has Bipartite toxins that bind to a receptor with one portion, allowing the release of the other portion into the host cytoplasm
Inhibits cell protein synthesis
Heart damage
Nerve paralysis
Shigella dysenteriae enterotoxin (neurotoxin):
Induces fluid loss from intestine and
Induces vascular endothelial damage in brain
Causes diarrhoes and neurological disturbances

16. EXOTOXINS Vibrio cholerae enterotoxin:
Has Bipartite toxins that bind to a receptor with one portion, allowing the release of the other portion into the host cytoplasm
Activates adenyl cyclase, and raises CAMP level in cells
Acts on intestinal epithelial cells
Causes water and electrolyte loss into the intestine

17. EXOTOXINS Bacillus anthracis complex:
3 factors form a toxic complex and cause;
Increased vascular permeability
Causing oedema and haemorrhage (primary lesion) and
Circulatory failure (systemic disease)

18. EXOTOXINS Clostridium botulinum toxin:
Blocks release of acetylcholine, leading to;
Neurotoxic signs
paralyses

19. EXOTOXINS Streptococcus pyogenes
erythrogenic toxin: Causes vasodilation
Streptococcus leucocidin and streptolysins:
These kill phagocytes- antiphagocytic activity
Streptokinase – lyses of fibrin
This is an aggressin – which is a bacteria enzyme which alter the local environment to the benefit of the organism
Hyaluronidase – liquifies connective tissue matrix
These two, promote spread of bacteria in tissue

20. EXOTOXINS Staphylococcus aureus atoxin:
Cytotoxic, Action on cell membranes – causes necrosis at the site of infection; systemic toxicity
Staphylococcus aureus leucocidin – kills phagocytes, thus is antiphagocytic
Staphylococcus aureus enterotoxin
Acts on vomiting centre in brain- causing nausea, vomiting, diarrhoea (food poisoning)

21. ENDOTOXINS These form part bacterial cell wall
The word endotoxin generally refers to the complex phospholipid-polysaccharide –protein complex macromollecules associated with cell wall
The lipopolysaccharide (LPS) is the important important component
LPS is commonly found in gram-negative bacteria

22. ENDOTOXINS The LPS of gram-negative bacteria consists of 3 components;
A core polysaccharide common to many gram-negative bacteria,
An O specific polysaccharide which confers virulence and serological specificity on the macromolecule and
A lipid A component manly responsible for toxicity
Endotoxins are also pyrogenic

23. Bacterial adhesins
Some strains of bacteria e.g. E.coli and Neisseriae have found to have hair-like filaments or fimbriae which assist them to attach themselves to body surfaces, with obvious survival benefits to these particular strains