bacterial pathogens Flashcards
define infection
is the growth & multiplication of a microbe in a body with or within disease
define disease
disease occurs when infections disrupts the normal functioning of the host
define pathogenicity?
is the capacity of a bacteria to cause disease
define virulence?
is the measure of the pathogenicity of the microorganism
define pathogenesis
refers to both the mechanisms of infection & the mechanism by which disease develops
what determines host susceptibility to bacterial infection?
- determined by host defences & bacterial virulence
- host defences can be compromised by destruction of barriers or defects in the immune response
what are opportunist pathogens?
- are typically members of normal flora & typically cause disease when they are introduced into an unprotected site
- usually occur in animals with an underlying condition
what are strict pathogens?
- are more virulent than opportunistic pathogens & cause disease in a normal healthy animal
what 5 attributes of a bacteria contribute to disease?
- access to host
- able to adhere & colonise the surface of the host
- invasive
- able to survive or evade host defence mechanisms
- able to produce harm to host tissues
what are the main portal of entry that bacteria use as access to the host?
main portals of entry are via the:
- mucous membranes
- skin
- parenteral
- many microbes have a preferred portal of entry & must entry a specific way & in a certain place to cause disease
how do microbes adhere to a surface of host?
- pathogens have adhesions or ligands that bind specifically to host cell surface receptors
how do bacteria colonise in a host?
- bacteria colonise by reproducing via binary fission
- must survive & reproduce despite hosts defence mechanisms
how are bacteria invasive (penetrate into host cells)?
- bacteria produce invasions which alter the actin filaments of the host cytoskeleton, allowing microbe to enter cell
- some use active phagocytosis
- bacteria can use microbial enzymes to invade cell (lyse cells, form or dissolve clots or dissolve materials in tissues)
how can bacteria evade the host immune system?
- interfering with phagocytosis by possessing a non-antigenic capsule
- interfering with phagocytic killing
- avoiding antibodies or complement
how can bacteria harm the host
bacteria can harm the host by:
- direct damage
- hypersensitivity reactions
- toxins (exotoxins & endotoxins)
how do bacteria harm the host by direct damage?
- by inducing cells to engulf the bacteria cell & once engulfed, its metabolism & multiplication kills the host cell
how do bacteria harm the host by hypersensitivity reactions?
- by causing an immune response that is more excessive than normal to a point where it leads to damage or is potentially damaging to the host
how do bacteria harm the host by toxin production?
- toxins are poisonous substances produced by microbes
define toxigenicity?
- is the ability of a microbe to produce toxins
define toxaemia
- is the presence of toxins in the blood
define toxic effects
fever, cardiovascular problems, diarrhoea, shock, destruction of RBCs & blood vessels & nervous system disruption
describe exotoxins?
- exotoxins are produced inside gram-positive bacteria as a part of their growth & are metabolised & excreted
- are soluble in body fluids & are rapidly transported throughout the body in blood or lymph
- responsible for disease symptoms & death
- antibodies called antitoxins provide immunity against exotoxins
define toxoids
- are toxins that have been altered by heat or chemicals & are used as vaccines for diphtheria & tetanus
describe endotoxins
- are part of the outer portion of the cell wall of gram negative bacteria
- endotoxins are present in Lipid A of the outer membrane
- are released when bacteria die & cell wall breaks apart
- do not promote the formation of effective antibodies
define infectious disease
- an infectious disease occurs when the presence of a living organism in or on the animal induces abnormal function that leads to clinical signs
what does a bacteria’s pathogenicity depend on?
- its ability to invade the host, multiply in the host & avoid being damaged by the host’s defences
what does a bacteria’s pathogenicity depend on?
- its ability to invade the host, multiply in the host & avoid being damaged by the host’s defences
- number of infectious organisms entering
- susceptibility of host
- virulence of pathogen
what are non-pathogens?
- microbes that are not pathogens
- considered the first line of defence in host defences
- commensals that become opportunists due to failure of host defences, introduction to an unusual site or disturbance of normal flora
- secondary infection
what is the carrier state?
- an animal is in a carrier state when it harbours a disease organism in its body without clinical signs & acts as carriers of infection
- may shed disease agent continuously or intermittently
what is a dormant/latent infection?
- is an infection that lies dormant in the body for a period of time but may become active under certain circumstances
- can persist without shedding or shed occasionally
what are chronic/persistent infections?
- infections that have been present for a long time or keeps recurring
- develop after acute infection
acute infection vs subacute infection
acute infection
- has a short severe clinical course of a few days & invading bacteria are usually cleared from the body by the host’s immune system
subacute infections
- produce clinical effect to a lesser intensity
what is septicaemia?
- is the presence of bacteria & toxins in blood
- caused by invasion of the bloodstream by virulent microbes
- pathogenic microbes multiply & persist in blood stream to produce systemic disease
define bacteraemia?
- temporary presence of bacteria in blood
- bacteria are only present transiently in bloodstream & don’t replicate
