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MLT-Pathogenicity

Mircrobiology

QuestionAnswer
What is pathogens? A microbe whose relationship with its host is parasitic and results in infection and disease.
What is pathogenicity? The potential of an organism to cause infection or disease.
What is virulent factor? Any characteristic or structure of the microbe that facilitates to establish itself in the host, and cause damage.
Example of True pathogens? Influenza virus, Poliovirus, Neisseria gonorrhoeae, Rabies, Malarial parasite
Example of opportunistic pathogens? Candidas albica, E.coli, Staphylococcus aureus, Pseudomonas
The infectious doesage of a pathogen? Coxiella burnetii (Q fever) - 1 cell Mycobacterium tuberculosis (TB) - 10 cells Neisseria gonorrhoeae (Gonorrhoea) - 1,000 cells Salmonella typhi (Typhoid) - 10,000 cells Vibrio cholera (Cholera) - 1,000,000,000 cells
Anti-2nd line defence(1)? -Killing Phagocyte -Produce leukocidins, causes the lysosomes of pahagocytes to lyse -self-destruction of WBC -Staphylococci and Streptococci
Anti-2nd line defence(2)? -Inhibition of chemotaxis -Produce chemicals that can interfere the movement of phagocytes towards the bacteria -Staphylococci and Clostridia
Anti-2nd line defence(3)? -Escape from phagocytes -Possess a capsule which favours the organisms to slip away from the phagocytosis, eg. Streptococcus pneumoniae -Some produce Coagulase, the clot act as the shield for the microbes from phagocytosis, eg. Staphylococcus aureus
Anti-2nd line defence(4)? -Resistance to digestion in phagocyte -by producing antioxidants, catalase in Staphylococci -have waxy cell wall which is resistant to enzyme digestion, e.g. Mycobacteria
Anti-2nd line defence(5)? -Inhibition of complement -deposit sialic acid residues on their surfaces which prevents opsonization by complement components and impedes recognition by phagocytes
Anti-3rd line defence(1)? -Inactivation of Antibody -Streptococcus pneumoniae -> IgA protease -> cleaves the Fc portion from IgA, no phagocytosis Staphylococcus aureus -> Fc portion receptor (Protein A) -> bind the antibody “upside down” -> no opsonization and phagocytosis
Anti-3rd line defence(2)? -Hiding -Malaria parasite in red cells, which cannot present the foreign antigen to T cells -where areas no Ab, like Salmonella in the bile duct, rabies the salivary gland
Anti-3rd line defence(3)? -Modifying the surface antigen -Antigenic drift -Antigenic shift -eg.Influenza
Anti-3rd line defence(4)? -Immunosuppession -Human Immunodeficiency Virus (HIV) target CD4+ T lymphocytes (T helper cells), causing lysis -no B cells and cytotoxic T cell activation.
How does pathogens causing diseases? 1.Direct damage: -secrete extracellular enzyme -produce exotoxins, endotoxins 2.Indirect damage -induce excessive or inappropriate host respond
How do the extracellular enzymes work? 1.To dissolve the host’s defence barriers and promote the spread of microbes to deeper tissues. eg: Mucinase, Keratinase 2.To protect the microbes from immune response. eg. Coagulase
How does Mucinase work? Digests the protective coating on mucous membrane in the gut -> Dysentery
How does Keratinase work? Digests the principle components of skin and hair, and is secreted by fungi -> sore and itchy skin
How does Coagulase work? Catalyze the formation of blood clot, which serves as a shield for the microbes from being engulfed -> blockage of blood vessel.
What is an exotoxins? A toxin molecule secreted by a living bacterial cell into the infected tissues.
Whats the examples of exotoxins? Haemolysin: disrupt cell membrane of red blood cells e,g, Streptolysin (Streptococcus pyogenes), α and β toxin (Staphylococcus aureus)
What is the function of neurotoxin botulinum (Botox)? Produced by Clostridium botulinum. The toxin prevents the transmission of nerve-muscle stimuli -> muscle paralysis
What is an endotoxin? A toxin that is not actively secreted but shed from the outer membrane.
What is the example of endotoxin? Lipopolysaccharide (LPS), a component of outer membrane of gram negative cell walls.
Whats the effect of endotoxin? Cause fever, inflammation, haemorrhage and diarrhea.
What would happen if blood infection by gram-negative bacteria such as E. coli, Salmonella, shigella? Fatal endotoxic shock
What is an excessive or inappropriate host respond? The capsule of Streptococcus pneumoniae prevents the bacteria from phagocytosis ->continuous influx of fluid into lung space -> Pneumonia
What are Superantigens? It is a bacterial secretion, capable of activating T-Cells at a rate 100 times greater than ordinary antigens -> overwhelming release of cytokines and cell death ->Toxic Shock syndrome
What is a mixed infection? One microbe creates an environment that favours another microbe to invade. Rhinovirus (Primary infection)-> Streptococcus pyogenes(Secondary infection)
Created by: kencho
 

 



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