Lecture 11: Activities of pathogens part 2 Flashcards
What are the three factors to consider when it comes to pathogen impact?
Susceptible host
Pathogen
Environment
What is a pathogen?
Microbe capable of causing disease
What are virulence factors and some exampels?
Virulence factors; The genetic determinants that allow a pathogen to cause disease.
i. e
- Adherence
- Invasion
- Immune evasion
- Toxins
What is virulence?
The capacity to cause disease in hosts with intact defences.
What sort of disease can bacteria cause?
Pyogenic infection Granulomatous/Chronic infection Intoxication Immune mediation Cancer
What is bacterial pyogenic infection?
Acute inflammation that leads to pus formation.
Tissue invasion, multiplication and immune response in sterile sites. i.e N. meningitidis enters CSF and provokes innate immunity = Meningitis.
What is granulomatous/chronic infection?
Bacteria that have evaded innate immunity thus cellular immunity is required.
Activated macrophages fuse and surround the antigen: Incomplete host response = Granuloma i.e Mycobacterium TB or symphilis
What is bacterial intoxication?
- Change in host physiology i.e vibrio cholerae toxin
- Tissue destruction i.e clostriudium perfringes, Gas gangrene (myonecrosis) caused by histotoxin which splits phospholipids.
What is bacterial immune mediation?
Antigen mimicry
I.e strep pyogenes pharyngitis, glomoerulonephritis and rheumatic fever
How can bacterial infection lead to cancer?
H. pylori can lead to stomach cancer.
Hep B -> liver cancer
Describe how cholera can result in diarrhoea;
Vibrio cholera from unsanitary water can divide in the bowel and release toxins. These toxins inhibit GTPase enzyme in enterocytes. This results in raised cGMP and this drives CFTR insertion into the membrane and loss of Cl ions which drives loss of Na and water. = Profuse diarrhoea.
How is an appendicitis triggered?
Appendix becomes obstructed by little faecolith (stone like material, immune cells, bacteria, dead bacteria etc) and the bacteria propagate resulting in inflammation of the appendix.
How does phagocytosis kill bacteria?
Phagocytes engulf bacteria and toxic granules fuse with the phagosome to form a lysosome
Bacteria are then killed within the lysosome i.e by hydrogen peroxide.
How is pain felt by the appendix?
Initially the inflamed appendix is sensed in the umbilical region before the inflammation spreads to the parietal peritoneum where the pain is now sensed in the right iliac fossa / right groin.
What are the outcomes of an enflamed appendix?
The inflamed appendix is encased by the omentum and forms a chronic inflammatory appendiceal mass.
If the appendix ruptures this can lead to peritonitis, sepsis and death.
How is an appendix managed?
Diagnosis Pain relief Fluids Surgery Antibiotics, inferior to surgery. Also given peri-operatively to reduce the risk of surgical wound infection.
What is streptococcus pyogenes responsible for?
Pharyngitis (sore throats) and cellulitis of the skin.
Rarely can result in rheumatic fever or glomerulonephritis.
Are antibiotics useful against Strept. Pyogenes?
Not useful for sore throat strep because only 15% of sore throats caused by this and they get better at same rate as virus’ i.e better safer than sorry
How does rheumatic fever present?
- Painful joints (cardinal symptom) but no bact. present in joint.
- Fever
- Inflammation of connective tissue and muscle in the heart (repeat episodes can cause severe damage) (‘M proteins’ of strep. pyogenes are cross reactive)
- Rash
- Chorea (Riving movements, benign)
How does penicillin act?
Penicillin inhibits transpeptidase found in bacteria.
Transpeptidase in bacteria removes the 5th AA on N-acetyle muramic acid (making up cell wall) to form a peptide chain between NAM particles giving the cell wall structure.
Thus it weakens the cell wall integrity.
Whats the difference between gram bacteria?
Gram positive = thick cell wall
Gram negative = thin cell wall
What leads to the resistance of bacteria?
Over-prescription drives bacterial resistance
- In complete dose
- Viral infections
