lecture 3) concept of virulence and infectivity Flashcards
define what is meant by the term disease
growth of pathogens that impairs tissue function
give an example of a disease in plants
rice blast fungus
what does the rice blast fungus do and what is it’s impact?
it is a plant disease that kills one of the most important food sources in the world
more rice means more people can eat which has an impact on the price of rice
name 3 different types of disease
genetic (aka metabolic)
disease of ageing
infectious disease
describe and given an example of a genetic disease
eg. cystic fibrosis
those with CF have a specific genotype due to impaired transport of Cl- across the cell membrane
describe and give an example of disease of ageing
eg. atherosclerosis
build up of plaque/cholesterol over a period of time
the older you are the more plaque will have built up in your arteries therefore based on age
describe and give an example of an infectious disease
eg measles
individual contracts outside agent
describe the MMR vaccine debate
we are close to eradicating the disease in the UK
people feared taking the vaccine would do you more harm than good
people stopped taking the vaccine
lead to measles outbreaks
define the term infection
a pathogen invades the host and begins growing in the host
what is a latent infection?
when a pathogen invades a host but doesnt cause disease
a disease is only caused when there is tissue impairment
give examples of latent infections
herpes, HIV, TB
name 3 possible ways infections can spread
skin to skin contact (mites) body fluids (HIV) water droplets (legionella)
why is legionella so dangerous?
can be fatal as it is latent in the environment but can cause disease once inside the host
define the term pathogen
an organism that is capable of causing disease in a susceptible host
what is characteristic of the pathogens in normal microbiota?
they dont cause disease
what is a true pathogen?
an infectious agent that causes disease in virtually any susceptible host
what is an opportunistic pathogen?
potentially infectious agents that cause disease in individuals with healthy immune systems
eg candida; may cause disease in those who are immunocompromised, when in the presence of MRSE - v toxic
define the term pathogenicity
the capacity of the microbe to cause disease
what are some of the characteristics of pathogenicity?
microbial variable
discontinuous variable - either is or isnt pathogenic
only expressed in susceptible host therefore dependent on host variables
list 4 host variables
age
diet
stress
status of immune system
define the term virulence
amount of damage or disease that can be caused to the host
how would you measure virulence?
the unit is cells kills/those that caused disease
what does ID50 stand for?
the median infective dose
the amount of microorganism that will produce demonstratable infection in 50% of it test subjects
what does LD50 stand for?
quantity of agent needed to kill 50% of test subjects
are ID50s and LD50s the same for every microorganism?
no, ID50s and LD50s vary for each microorganism as some are more virulent than others eg TB vs C. diff
name 3 influences of virulence
immunological status
physiological status
route of infection
name 3 routes of infection
ingestion
skin
inhalation
name 3 host influences on virulence
age
genetics
stress
using an example, explain how the route of infection can determine the virulence of a pathogen
anthrax
cutaneous; found on the skin, causes sores, can be treated
inhaled; same number of spores inhaled as on the skin can kill you. inhaled anthrax has a lower ID50
what is the impact of climate change on disease?
new climate = new diseases = new plant diseases = migration
what is a virulence factor?
describes a microbial characteristic
caused by specific genes
intrinsic factor
outcomes dependent on host
what is the first of koch’s molecular postulates?
the gene under investigation should be found in all pathogenic strains of a species but absent from non-pathogenic strains
what is the 2nd of koch’s molecular postulates?
the gene causing the virulence but be expressed during infection
what is the 3rd kochs molecular postulates?
inactivation of the gene causing virulence must lead to measurable loss of virulence
this loss must be less in microorganisms with unaltered gene
what is the 4th kochs molecular postulate?
reversion or allelic replacement of mutated gene should restore pathogenicity
how would you monitor gene expression using RNA sequencing?
sequence of the gene known
primer made to stick to product using 16S rRNA method
measure light emitted from the number of copies from a gene
what is the copy number in PCR?
how many pieces of RNA is expressed at a certain time
what is a limitation of the virulence factor concept?
hard to apply to microbes whose pathogenicity is limited (immunocompromised)
what is meant by the term planktonic when describing bacterial state?
bacteria are in the aqueous phase
not stuck on a surface
what is meant by the term biofilm?
bacteria are attached to a surface
what is characteristic about the genetics between biofilms and planktonic bacteria?
they have different gene expression as they know if they are on a surface or not
what is more susceptible to antibiotics; planktonic or biofilm bacteria? why?
planktonic more susceptible to antibiotics as a lower concentration of ABs needed
harder for AB to enter into middle of biofilm to target the bacteria
eg metal hip replacement: biofilm forms around the metal hip causing infection, no blood flow around the metal hip to take anti-microbial therefore need to repeat the surgery
what is the impact of biofilms on the oil industry?
microbes attach to the steel and form biofilms
biofilms corrode the pipes
pipes then need to be replaced - expensive
why would a microbe not have the same impact when grown in the presence of another microbe vs being grown individually?
more profound when together
why would you need to find out what microbe it is that is causing infection when in the presence of other microbes?
need to find out what microbe it is causing the infection in order to treat it
different microbes require different treatment plans
how would you find out what microbe is causing the infection when in the presence of another microbe?
look at its virulence factors
what is cell-cell signalling?
different ways cells communicate using different chemicals they produce
where does the name quorum sensing come from?
need a certain number of organisms to be present before chemicals are produced
what is quorum sensing?
a type of cell-cell communication
chemicals thrown into environment (signal)
microbes sense the signal and move towards it (food sources, upregulate virulence factors)
what is quorum sensing an example of?
cooperation
what is the principle behind social organisation of bacteria?
some bacteria produce products needed by all bacteria
other bacteria dont produce these essential produce but use what the other bacteria have produced (cheaters, sense of hierarchy)
happens especially in biofilms
what is the evidence for electrical signalling between bacteria?
some form networks and can move electricity from one place to another
could we harvest this electricity?
is it an example of neural activity?
what is meant by the term epidemiology?
the effects of pathogens on populations
a measure of when and where they occur
define the term incidence
the number of new cases of a disease in a given area/population
define the term prevelance
the total number of new and existing cases
how are incidence and prevelance expressed
as a ratio
I:P
