microbiology how bacteria cause disease Flashcards
define pathogen
an organism that is capable of causing the host damage or disease
define opportunistic pathogen
an organism that is a member of the resident microbiota or normally inhabiting the external environment that causes infection under certain circumstances
define symbiont
a member of the resident microbiota that confers benefit to the host
define pathobiont
a member of the resident microbiota which confers damage to the host
define dysbiosis
imbalances in the resident human microbiota or our responses to them
describe pathogenicity
the degree of virulence of a microbe to cause damage in the host
define virulence
relative capacity of the organism to cause damage in the host
define virulence determinant factor
component of the pathogen that damages the host
define lethal dose
LD50 is the number of pathogens required to kill 50% of the host
what is the major steps of virulence mechanisms
• Transmission
• Adherence to host surfaces
• Invasiveness
Toxigenicity
describe transmission
infections can be acquired by an internal or external sources eg ingestion inhalation trauma needle stick sexual transmission
what are the four portals of entry for transmission
skin
resp tract
GU tract
GI tract
describe adherence to host surfaces
some fungi and bacteria produce substances that help with adherence
critical for colonisation
give examples of bacteria requiring adherence to host surfaces
N gonorrhoea and E coli with pili
S mutans- Extracellular polysaccharide layer helps it adhere
what is quorum sensing
molecules(homoserine lactone) are secreted by bacteria in biofilm
It is a cell-cell communication which allows bacteria to share information about cell density and adjust gene expression accordingly
May lead to reduction in metabolic activity or other genes being expressed
describe invasiveness
It is important and depends on bacterial enzymes
Eg collagenase and hyaluronidase
Allows for the breakdown of intercellular structures and allows for bacteria to enter straight easily though tissues
where is hyaluronidase present
in S aureus and S pyogenes
where is collagenase present
present in clostridium perfringens
what does a clot inhibit
phagocytosis and immune responsee has no access
how do coagulase and kinase work together
→ The bacteria produce coagulase
→ The clot forms inhibits phagocytosis, immune response has no access, antibiotics are not effective
The bacteria later produce kinase which dissolves the clot and releases bacteria
describe immunoglobulin protease
degrades IgA on mucosal surface and allows bacteria to adhere
what are leukocidins
they can destroy immune host cells such as neutrophilic leukocytes and macrophages
describe toxigenicity
two types of toxic
endotoxins
exotoxins
what are endotoxins
are the lipid portions of the LPS that are part of the outer cell wall of the gram -ve bacteria
what are the biological effects of endotoxins
→ Fever- release of IL-1 from macrophages
→ Hypotension, shock and perfusion of major organs- due to vasodilation
→ Inflammation
→ Tissue ischaemia
→ Increased phagocytic activity of macrophages
Increased antibody production
why do the biological effects of endotoxins occur
due to the host factors producing IL-1 and TNF from macrophages
what can occur in +ve bacteria
endotoxin like effects- occur from trichroic acid or peptidoglycan which can release TNF and iL-1
describe exotoxins
Produced by both gram +ve and gram -ve bacteria
Mostly by gram +ve though
Secreted and released into the environment via lysis
give examples of neurotoxins
Tetanus, diphtheria and botulinum toxins are neurotoxins
how do exotoxins cause disease
they can cause disease to a distant part of the body due to the exotoxin diffusing
what does the tetanus toxin cause
locked jaw or masseter muscle spasm
what does tentanospasmin cause muscle spasms
prevented the release of inhibitory neurotransmitter glycine which causes muscle spasms
describe the botulinum toxin
one of the most toxic compounds
how does the botulinum toxin work
The toxin blocks the release of acetylcholine at the synapse and leads to paralysis of the muscles
○ It is an obligate anaerobe and endospore former( may transform into a spore in harsh environments to protect itself)
what are the symptoms of botulism
→ 1-2 days after ingestion → Descending motor loss with flaccid paralysis → Diplopia → Dysphagia → Speech problems → Dry mouth → Resp failure → Death
what is the bacterium that causes cholera and its endotoxin
vibrio cholerae
endotoxin is enterotoxin
what is the bacterium that causes diphtheria
corynebacterium diphtheriae
what is the bacterium that causes diarrhoea, pseudomembranous colitis
c difficile
what is the bacterium that causes haemorrhage colitis and its endotoxin
e coli O157
endotoxin is verotoxin
what is the bacterium that causes whooping cough and its endotoxin
bordetella pertussis
pertussis toxin
what is the bacterium that causes scarlet fever
strep pyogenes
exotoxins
what is the bacterium that causes scaled skin syndrome and the endotoxin
s aureus
endotoxin - epidermolysin
what are bacterial virulence factors
adhesin invasin impedin modulin aggresin
what is adhesin
enables binding to host tissue
what is invasin
enables invasion of host cell/tissue
what is impedin
enables avoidance of host defence mechanism(s)
what is aggresin
causes direct damage to host
what is modulin
induces indirect damage by perturbing regulation of host defences
