Pathogens and the host: variously invasive pathogens Flashcards
How can virulence be measured?
From experiemental studies - lethal dose
Highly virulent pathogens show little difference in number of cells needed to kill 100% of population compared to 50% of population
What is meant by lethal dose?
Lethal dose is the amount of agent that kills 50% of
What is meant by attenuation?
the decrease or loss of virulence
What is meant by invasiveness?
ability of pathogen to grow in host tissues at densities that inhibit host function - without producing toxin
Toxicity is means of causing damage to host via production of toxin. True or false?
True
Non-invasive pathogens involve viable bacteria but no penetration through epithelial layer. True or false?
True
Is diptheria an invasive or non-invasive pathogen?
Non-invasin
Diptheria bacteria are gram negative. True or false?
False - gram positive
Non-invasive pathogens are localised at point of entry or mediated by exotoxins. True or false?
True
Explain the pathogenisis of diptheria
Inhalation of aerosol - colonisation in throat
Produces single chained A-B toxin
Psuedomembrane forms in throat and A-B toxin inhibits elongation factor 2 in eukaryotic cells. This inhibits protein synthesis and therefore kills cell
Is pertussis bacteria are gram positive. True or false?
False - gram negative
DIptheria causes difficulty swallowing. True or false?
True
Explain the pathogenisis of pertussis bacterium.
attached and replicate on ciliated upper respiratory tract mucosa
toxin production: pertussis exotoxin, trachael cytotoxin, invasive adenylate cyclase toxin
these cause loss of mucociliary clearance, violent coughing fits and secondary pneumonia
How many toxins does the pertussis bacterium produce?
3
Is pertussis bacterium invasive or non-invasive?
Non-invasive
Is cholera bacterium gram positive or negative?
gram negative
Explain the pathogenisis of cholera bacterium
Acute infection of GIT (small intestine)
production of cholera toxin - causes upregulation of adenylate cyclase and loss of fluid from GIT -> death through dehydration (unless prevented by rehydration therapy)
What is meant by a partially-invasive pathogen?
Invade epithelial layer but don’t penetrate deeper tissue. They invade at primary site of infection only
Are shigella bacteria gram positive or negative?
Negative
Do shigella bacteria form spores?
No
What is the clinical presentation of shigellosis?
Blood and puss in diarrhoea
Explain the pathogenisis of shigella bacteria
attachment and invasion of ileum and colonic epithelia
produces A-B toxin
invasion is no deeper than lamina propria
Invasive pathogens cause minimum damage at primary site of infection. True or false?
True
How do invasive pathogens spread to lymphatics?
via lymph
Is enteric fever caused by an invasive or non-invasive pathogen?
Invasive
How is enteric fever transmitted?
Person-person or through consumption of contaminated food
Enteric fever can be spread by animal reservoir. True or false?
False
Explain the pathogenesis of enteric fever bacterium.
Bacterial induced uptake via M cells - travel through epithelia and cause systemic dissemination
In food poisoning, is bacterial colonisation present?
No
Food poisoning occurs on consumption of food contaminated with toxins of chemical or bacterial origin. True or false?
True
Which bacteria causes botulism?
Clostridium botulinum
Clostridium botulinum is gram positive. True or false?
True
The botulinum bacteria is spore forming. True or false?
True
Staphylococcus aureus can cause skin infections and food poisoning. True or false?
True
How are symptoms produced by staph. aureus?
the bacteria produces an enterotoxin - toxin is ingested and interacts with gastric mucosa - symptoms
Bacillus cereus doesn’t form spores. True or false?
False
What are the two disease forms of bacillus cereus?
emetic toxin - heat stable, short incubation
enterotoxin - heat labile, longer incubation
