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bacterial pathogenicity
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- 1Infection and Disease- we live in balance with normal flora and external organisms
- if the balance is upset we get an infection
1. bacteria (potential pathogens) becomes established
2. penetrate defenses
3. invade tissues
4. multiply
5. produce clinical symptoms
Infectious disease; harmful alteration of physiology or metabolism caused by a microorganism or its products
- caused by a pathogen - 2Endogenous Infections- where the organism comes from determines wether a disease is endogenous or exogenous
- endogenous infections source from within the body
- normal flora displaced to where they don't normally exist - 3Congenital Infection- source of pathogen is mother
- in utero, crosses placenta: rubella, CMV, toxoplasmosis
- at time of birth, blood born pathogens: hep B, HIV - 4Exogenous Infections- organisms from the environment
Cross infection in hospital
- healthcare associated infections (hospital enquired)
- often serious infections; antibiotic resistance, host more susceptible
- most are from people in the community, if treated at home, stays in community - 5The Disease ProcessPathogenicity: capacity to produce disease
- depends on its ability to gain entry to host, attach to host issues, evade host defences, damage tissues and produce symptoms
Virulence = degree of pathogenicity and depends on organism
- indicated by how easily it enters host, measured by case fatality rates - 6Ebola Virus & Rabies- hemorrhagic fever
- spread by body secretion direct contact
- interferes with endothelial cells of blood vessels
- death within 7 days
- case fatality of ~90%
- Rabies ~100% case fatality if untreated - 7Infective Dose- a virulence factor
- number of cells required to enter the body to cause disease
- body destroys organism when only a few cells but if they are in large numbers then organism becomes established
- stomach acid normally kills most bacteria, however if food is heavily infected with a pathogen then disease ensues
- the more virulent an organism is, the less numbers it needs to evade the host - 8Adherence- the way that bacteria sticks
- the most important disease causing characteristics or some bacteria, particularly those that invade via mucous membranes
- body attempts to rid by sneezing or coughing so they need to stick
- adhesions on bacteria allow them to stick to chemicals on host cells - 9Slime Layers- secrete sticky residue
- can form multiple layers - biofilm
- cements bacteria together
- sticks the layer of bacteria to the surface - 10Biofilms- also forms on medical devices - replacement heart valves, endotracheal tubes, urinary catheters, etc.
- difficult to remove
- protected from host defences because the glycocalyx forms a physical barrier that human defence cells have difficulty penetrating
- bacteria in biofilms are much less susceptible to antibiotic therapy because of the diffusion barrier created by the layer of polysaccharide - 11Toxins- produced by some microorganisms
- interfere with normal functioning of host cells or tissues
- not all microorganisms produce toxins
- for some bacteria most important determinant of their ability to cause disease
- lose ability to produce toxins = lose pathogenicity
- viruses do not produce toxins - 12Exotoxins- toxins secreted into the environment in which the bacteria are growing
- produced by some bacteria
- usually are proteins
- heat liable
- secreted or released from the bacterial cell
- each has a specific effect on host cells
- moderate to high toxicity - 13Exotoxins- some bacteria produce a single exotoxin
- others produce many toxins with different effects
- some exotoxins are extremely potent and include some of the strongest poisons known
- most secrete toxins while growing - 14Endotoxinstoxins that form part of the outer membrane of gram negative bacteria; not actively secreted but are released when the bacterial cell is damaged or dies
- 15Toxins That Break Down Cells- many exotoxins damage host cells by lysis
- damage host cell membrane structure or inserting themselves into the cell membrane, creating pores or channels
- water enters, cells swell and burst - 16Bacterial Haemolysis- many toxins damage red blood cells = haemolysins
- bacteria that secrete haemolysins are grown on culture media containing blood
- distinct zones of red cell clearing can be seen around the bacterial colonies
- the soluble exotoxins diffuse into the agar and cause destruction of red cells around the colony
- useful in the identification of some bacteria - 17The mode of action of cholera toxin- exotoxins that alters the regulatory control in cells
- binds specifically to intestinal epithelial cells
- enters the cell and causes increased and uncontrolled production of cydic AMP
- increased cydic AMP cause uncontrolled secretion of chloride and bicarbonate ions from the epithelial cells
- massive outflow of water from the cells into the lumen of the intestine
- profuse diarrhoea
- die from extreme dehydration - 18Toxins that affect the nervous system- the neurotoxins of the anaerobic bacteria clostridium tetani and clostridium botulinum are two of the most potent toxins known
- C tetani usually grows in deep, necrotic puncture wounds where anaerobic conditions exist
- the bacterium itself does not spread far from the initial site of infection
- the exotoxin that it secretes travels to the CNS to cause severe neuromuscular dysfunction
- uncontrolled, rigid muscle contraction - 19Clostridium tetani toxin - Tetanospasmin- stops neurons from releasing inhibitory neurotransmitters
- the consequence of this is dangerous overactivity in the muscles from the smallest stimulus
- the failure of inhibition of motor reflexes by sensory stimulation
- causes generalised contractions - tetanic spasms - 20Toxins that act as super antigens- indiscriminately activate large numbers of T cells
- massive release of cytokines
- cause injury to host tissues and septic shock and suppress normal immune responses - 21Toxoids- exotoxins are proteins; antigenic
- stimulate the production of anti-toxins by the immune system; a specific antibody produced against a toxin, binds to the toxin and neutralises it, preventing it from binding to its target cell
- can be modified by heat or chemicals, to remove their toxicity but retain ability to elicit an immune response
- toxins modified in this way are called toxoids
- diphtheria and tetanus (DPT) vaccine - 22Antitoxins- can also treat exotoxin disease with antitoxins that neutralise the toxin already in the body
- from the serum of immune humans or animals
- tetanus and botulism
- also called specific immunoglobulin
- immediate neutralisation of the toxin before it is able to bind to target cells
- without antitoxin, patients may die because their immune system does not have sufficient time to make required antibodies - 23Endotoxins- LPS of the cell walls of gram negative bacteria
- only exert their effect once their cell wall breaks down
- during infection, small amounts of LPS released as older bacterial cells die
- death of bacteria and release of endotoxin can be greatly accelerated once phagocytes begin to digest them or antibiotics that kill the bacteria are administered
- antibiotics may initially increase LPS and thus cause a temporary worsening of symptoms - 24Endotoxins- involve some part of the immune system
- fever is one of the most common symptoms; stimulating the release of endogenous pyrogens from mononuclear phagocytes, act on the temperature-regulating centre in the hypothalamus to reset the body temperature set-point to a higher level
- other responses include muscle weakness, generalised aches, diarrhoea and malaise
- severe infection can cause septic shock; endotoxin induces the release of cytokines, which cause damage to blood capillaries and alters their permeability, fluid leak into the tissues = shock - 25Auto Immune Disease- can cause damage by inducing autoimmunity
- confuse the immune system so that self-tissues appear foreign
- the immune system may attack those tissues and produce an autoimmune disease - 26Evasion Strategies- do not directly cause tissue damage, but are responsible for the organism's pathogenicity, or ability to cause disease
- escape from phagocytes, block or avoid the process
- concealment, hiding inside cells or in 'privileged sites' where defence cells do not normally circulate
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- Fichas sobre bacterial pathogenicity, creado por annie.97 el 17/06/2016.
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