Pathogenicity Flashcards
name the steps of the basic life cycle of a pathogen?
- enter
- attach
- colonise
- evade host immunity
- produce harmful proteins
- disseminate
- release from host
describe the term pathogen.
organism capable of causing disease
describe the term commensal.
organism that is part of the normal flora
describe the term pathogenicity.
ability to cause disease
describe the term virulence.
ability to cause severe disease
eg. more virulent the more dangerous
what are microorganisms?
agents of infectious diseases
name 5 divisions of microorganisms?
bacteria
fungi
viruses
prions
parasites
what is colonisation?
when microbes find a new host and start to multiply
what leads to normal flora?
balance between colonised microbes and humans
what is a microbe that causes disease called?
infection
what is an endogenous infections?
when the source of microbe is a patients own flora
what is an exogenous infection?
when the source of microbe is flora from outside a patients body
give characteristics of koch’s postulates?
- microbe must be present in every case of disease
- microbe must be isolated from diseased host and grown in pure culture
- disease must be reproduced when a pure culture is introduced into a susceptible host
- microbe must be recovered from and experimentally infected host
what is koch’s postulates?
germ theory of disease
what does koch’s postulates prove?
how do microorganisms get into the body person to person?
- contaminated blood or bodily fluids
- touch
- saliva
- air
give 5 examples of how microorganisms get into a person?
- person to person
- fomites (surfaces)
- insects
- water
- food
what is attachment of a microorganisms specific to?
host and tissue
what allows e coli to attach to the bladder epithelium?
pili (fimbriae)
describe characteristics of pili (fimbriae) in e-coli?
- proteinaceous
- usually in gram negative
- 4-10 nm wide
- 0.5-4 um long
how are pili (fimbriae) in e-coli stuck to a surface?
covalently
how do UTI’s colonise?
faeces or perineal regions
who is most commonly after by UTI’s?
and what % of women develop a UTI at some point in their life?
females under 10 and between 20-40
50% of woman
what is the main defence against UTI’s?
flushing action of urine
which protein present in urine helps bind specific Escherichia coli strains in UTI’s (helpful)?
Tamm-Horsfall protein
which fruit helps protect against UTI’s?
cranberries
give 4 examples of encapsulated infections?
meningitis
pneumonia
otitis media
sinusitis
what is 4 things that commonly cause encapsulated infections?
streptococcus pneumoniae
haemophilus influenza
neisseria meningitis
group B streptococcus
what is on the outer layer of a gram positive cell and what does it do?
capsule layer
protection
what is the capsular function?
- helps mediate adhesion (colonise)
- helps immune evasion
- protects from desiccation (doesn’t dry out)
- receives carbs
- encapsulated bacteria gives rise to smooth colonies
- capsule material gives rise to capsular antigens
name the 2 types of toxins?
exotoxins
endotoxins
what are exotoxins?
produced inside gram positive bacteria as part of growth and metabolism.
secreted or released following lysis into surround medium.
what are endotoxins?
part of outer portion of cell wall of gram negative bacteria.
liberated when the bacteria die and the cell wall breaks apart.
what are LPS molecules detected by in gram negative?
macrophages
what is LPS in a gram negative cell wall?
lipopolysaccharides
is LPS endotoxin or exotoxin?
endotoxin
when are LPS released from a gram negative cel wall?
the cell lises and they are released
what is a common syndrome that LPS (endotoxin) can cause?
toxic shock
what are exotoxins?
proteins
are exotoxins and endotoxins, specific or non-specific?
endotoxins - non specific
exotoxins - specific
what is the difference between exotoxins and endotoxins in terms of potency and relationship to cell?
endotoxins = low potency, part of outer membrane of cell
exotoxins = high potency, extracellular/ diffusible (made inside and diffused out)
