Infection Flashcards
What is the definition of pathogenicity?
the capacity of a micro-organism to cause infection
What are the 4 requirements of an organism to have pathogenicity?
- transmissibility (ability of an organism to be transmitted from one individual from another) 2. establishment in or on a host 3. harmful effects 4. persistence
What is meant by persistence of a micro-organism?
the ability to subvert the immune system in some manner so it can persist for long enough to survive, reproduce and be transferred to another individual
What is the definition of virulence?
the degree to which a micro-organism is able to cause disease a more virulent organism will cause disease more readily
What is the definition of infectivity?
the ability of a micro-organism to become established on/in a host
What factors are involved in mediating infectivity?
- microbial ligand 2. host cell surface receptor
What is the definition of a virulence factor?
components of a micro-organism which aid its ability to cause infection encoded by virulence genes
What are examples of the actions of virulence factors?
- facilitation of adhesion 2. toxic effects 3. tissue-damage 4. interference with host defence mechanisms 5. facilitation of invasion 6. modulation of the host cytokine response
What are the 6 stages in the cycle of infection?
- encounter
- entry
- spread
- evade defences
- multiply and damage
- disperse

What factors can influence the cycle of infection?
the status of the host immune system can impact the speed and severity of the cycle
What is the difference between an endogenous and exogenous source of infection
Endogenous:
microorganisms already in the host body travel into a priviledge site (somewhere where they shouldn’t be)
Exogenous:
organisms originate from the external environment
What is bacterial pneumonia?
it is an infection of the lower respiratory tract that causes fluid to collect in the alveoli
this impairs gas exchange and leads to poor oxygen uptake

Which groups of people are more susceptible to bacterial pneumonia?
- extremes of age (old and young)
- immunocompromised individuals
What are the 3 main microorganisms which can cause bacterial pneumonia?
- streptococcus pneumoniae
- staphylococcus aureus
- haemophilus influenzae
What is gonorrhoea and what organism causes it?
What age group is most commonly affected?
it is an STI caused by Neisseria gonorrhoeae
peak incidence is 15-19 in women and 20-24 in men
What are the main symptoms of gonorrhoea?
- discharge of pus from the urethra
- burning sensation
- sterility
What is meant by gonorrhoea having a sex bias to symptoms?
90% of infected men show symptoms, but only 20% of infected women show symptoms
What is involved in the encounter stage when looking at bacterial pneumonia?
- inhalation of air-bourne droplets containing the pathogen
- contact with mouth of infected individual
- contaminated blood
What is involved in the encounter stage when looking at gonorrhoea?
- sexual contact with an infected individual
- contact with urethral exudate
- vertical transmission
What aids in the entry/colonisation of N. gonorrhoeae?
pilli facilitate attachment of the diplococci to the walls of the urogenital tract

What is a common molecule that many microorganisms adhere to?
What does this mean?
fibronectin
this is a common receptor on the surface of many cells meaning that the organism can cause infection in multiple parts of the body
What is the adhesin and receptor of N. gonorrhoeae?
adhesin - fimbriae
receptor - GD1 ganglioside
GD1 ganglioside is also found in the respiratory tract so it is possible to get gonorrhoea of the RT
What are the 2 different methods of entry of a microorganism?
Ingress:
organism gains access through a standard site that is open to the external environment
Penetration:
the breakthrough and introduction of the organism into a priviledge site e.g. through a scratch
What are the main components of a microorganism involved in spreading and evading defences?
- flagella
- capsule
- IgA protease
- pneumococcal surface protein A



