microbial pathogenicity and virulence Flashcards
(40 cards)
why bother studying infectious disease the mechanisms of pathogenesis?
antibiotics were introduced in the 1950s - before their introduction microbial infections were the leading cause of death worldwide
- in the beginning of the 20th century a better understanding of infections have meant there were better hygiene practices and this meant that infectious diseases started to be reduced but Infectious disease was still a leading cause of death.
- So in the 1950s antibiotics became widely available and they would just seen as a miracle drug as bacterial infections were now treatable
- so over the next few decades microbes weren’t really studied in terms of identifying new antibiotics new treatments.
why do microbial infections remain a leading cause of death and concern
- antibiotic/ drug resistance
- emerging and re-emerging infectious diseases
- large outbreaks of food-borne and water-borne infections
- hospital-acquired infections
- microbiota shift diseases
- bioterrorism
microbiota shift diseases
something we weren’t aware of until relatively recently is microbiota shift diseases. So we’re now much more aware of the importance of the microbiota in the microbiome, and we now know that shifts and your microbiota can cause diseases
emerging and re-emerging infectious diseases
there are 3 classes:
diseases caused by previously unidentified. microbes
- these are microbes that we are only recently aware have entered the human population
- covid-19 classic example of that
diseases known for a longtime but microbial cause only recently identified
- E.g We’ve always known about gastroenteritis being infectious, but it’s only recently that we’ve been able to culture the organism and then show that that’s responsible for the majority of cases of bacterial gastroenteritis.
old diseases that have returned due to conditions favouring their emergence
- this could be that antibiotic resistance or it could be changes in what we’re doing
factors associated with increasing incidence of diseases - modern medicine
- Modern medicines as a source of new disease
- opportunistic infections
- increase in immunocompromised patients
- nosocomial infections
- opportunistic infections
factors associated with increasing incidence of diseases - changing human practices
○ foodborne and waterborne diseases - globalization means we’ve got global distribution, which has an effect
○ and zoonotic infections - So zoonotic infections are transmitted from animals to humans.
factors associated with increasing incidence of diseases - rapid change in genetic makeup of microbes
-horizontal Gene transfer that allows movement of large sections of DNA so they can transmit virulence factors, antibiotic resistance genes easily between them
○ but also some organisms hypermutate, rapidly change and so can create new diseases so you might have it under control and then it mutates and then you need to control the new version.
septicaemia
Septicemia is where you get an infection within the blood and several organisms are responsible for septicemia.
- group A strep is one of those pathogens
Another organism responsible for septicemia sepsis is meningococcal meningitis
colonisation
ability of a microbe to remain at a particular location and multiply there
infection
successful colonisation and multiplication by a microbe capable of causing disease
disease
a dynamic process involving a sufficient change in the normal function of an organism’s cells or tissues to cause symptoms
pathogenicity
a microbes ability to cause disease
virulence
- the degree of pathology caused by a microbe
pathogenesis
mechanisms a microbe uses to cause the disease state
virulence factors
features that contribute to the ability of a microbe to colonise and cause disease
pathogen
a pathogen is a microbe capable of causing disease, but not all pathogens have the same ability to cause disease
- you either have true (primary) pathogens or opportunistic (secondary) pathogens
true pathogen
true pathogen is likely to cause disease in a healthy host - an infection of someone that’s not been previously immunized against it. So it’s someone meets that organism for the first time it will invariably cause disease.
opportunistic pathogens
○ these generally only cause disease in a compromised host.
○ So they’ve got a weakened immune system in some way
○ or it can be that that microbe enters an unusual site in a host
This is usually due to a breach in their immune system
how to prove that a particular microorganism causes a disease - robert koch
the person that came up with how To isolate and culture microbes and because of this it led him to come up with Koch’s postulates.
-these are referred to as the four Commandments of infectious disease
Kochs postulates
- the microbe must be associated with symptoms of the disease and be present at the site of infection
- the microbe must be isolated from disease lesions and grown as a pure culture
- cultured microbe should reproduce the disease when inoculated into a susceptible healthy host
- the microbe must be re-isolated from the host used in 3
Kochs first postulate
first postulate is that the microbe must be associated with symptoms of the disease or disease lesion and be present at the site of infection or present in the disease lesions, but not in healthy tissues or not in people without the disease.
-one of the problems with this is we now know that lots of diseases are Caused by organisms that are often commensals
- not everybody that has a particular organism on them necessarily gets a disease.
Kochs second postulate
○ the second postulate is that the microbe must be isolated from the disease lesions and grown as pure culture
- But as we know now there are loads of microbes We can’t culture
kochs 3rd postulate
○ Third postulate is that the microbes should reproduce a disease when inoculated into a susceptible healthy host
- now at the time that Robert Koch produced these postulates they were using human volunteers for these experiments And so this was quite straightforward
- now we would not do that and often animals are used as the host
- a lot of disease is a human specific. And so there’s no good animal model and so it’s very difficult to fulfill this postulate.
kochs 4th postulate
○ last one is that the microbe must be re isolated from the host used in three and
you can grow your culture
§ if you managed to fulfill the first three then this is very straightforward
§ and it’s important because what it does show is that it was actually that organism that you introduced that cause the disease
the fact you can re isolate it again means it has gotten their propagated course of disease.