Flashcards in microorganisms in disease Deck (100)
what is pathogenicity?
the capability of a microorganism to cause infection
what are the requirements to cause infection?
transmissibility, establishment in a host cell, harmful effects and persistence
what often causes more harm than the pathogen itself?
the harm mediated by the host response
what is virulence often used for?
interchangeably to describe pathogenicity - it is sometimes defined as the degree to which a micro-organism is able to cause disease - allows relative description of pathogenic potential
what is an example of virulence?
staphylococcus aureus and streptococcus mutans are both found in the mouth - S.aureus is more virulent as causes disease more readily
what is infectivity?
the ability of a micro-organism to become established on a host - mediated by microbial ligand and host cell surface receptor
what are virulence factors?
components of a micro-organism that aid it's ability to cause infection - infectivity and virulence
what are virulence factors encoded by?
how can you reduce the infectivity or completely stop it?
remove the virulence factors
what are examples of virulence factors?
tissue damage, facilitation of adhesion and toxic effects, interference with host cell mechanisms, facilitation of invasion, modulation of host cytokine response
what is the cycle of infection?
encounter, invade, spread, evade defences, multiply and damage and disperse
what affects the severity and speed of the infection cycle?
the status of the host's immune system
how can you control infection?
interrupt at each stage of the infection cycle - understand the processes occurring at each stage is important for this
where can you get infections from?
endogenous - microorganisms that get from the wrong place into the host - many individuals who are already in hospital
exogenous - organisms originating from the external environment/infected individuals - receptors on cells can change in level meaning that the pathogen can opportunistically come in
what is bacterial pneumonia?
infection of the lower respiratory tract that causes fluid to collect in the alveoli of the lungs
what is the epidemiology of bacterial pneumonia?
around 4 million people die annually from pneumonia, mainly the old or young or immunocompromised
what are the main organisms that can cause bacterial pneumonia?
streptococcus pneumoniae, staphylococcus aureus, haemophilius influenza - gram positive can survive the environment
what is gonorrhoea?
it is a sexually transmitted infection that is caused by neisseria gonorrhoeae
what is the epidemiology of gonorrhoeae?
it is the second most common STI in the UK - peak incidence in 15-19y/o for women and 20-24y/o in men
what are the symptoms in gonorrhoea?
discharge of pus from the urethra, burning sensation and sterility
what is the sex bias of gonorrohoea?
sex bias to symptoms - 90% of men show but only 20% of infected women - untreated can form more severe forms
how can you encounter bacterial pneumoniae?
inhalation of air borne droplets containing pathogen - encounter right tissue type, adhere and cause infection, mouth contact with infected individual and contaminated blood
how can you encounter gonorrhoea?
sexual contact with infected individuals - horizontal transmission - contact with urethral exudate and vertical transmission from mother to child
what types of entry/colonisation are there?
ingress or penetration - getting break through and introduction of organism `
how can you get gonorrhoea of the throat?
the GD1 ganglioside can be expressed in the respiratory tract and adhesins are involved in determining the tissue tropism of bacterial infection
what are examples of evading defences?
pneumococcal surface protein A, capsule, flagella dn IgA protease
what is a capsule?
it is a layer of polysaccharide found on the outside of pathogens that prevents the phagocytosis and complement mediated killing of pathogens - they can move through mucus
how will india ink stain show if a bacteria has a capsule?
negative test - capsule means ink cannot go up to border so can be seen easily
what is C3b used for?
cytolysis and opsonisation