Sunday 24th June 2018
Past Research

Cystic Fibrosis Research

MR ROSS PALLETT

 

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PROJECT TITLE – Using an in vitro model of human cystic fibrosis airways to investigate bacterial strategies which inactivate defence mechanisms and increase infection

PROJECT TIMESCALE:  1 July 2014 – 30 June 2017

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UPDATE:  3 MARCH 2017

Ross Pallett

At Aston University we are using cell culture models of the lungs to investigate the response to infection. Our research is focused on how disease-causing bacteria (pathogens) interact with each other to influence the course and severity of infections. We are particularly interested in the types of bacteria that infect the lungs of children with cystic fibrosis (CF). Lung disease is the main cause of death for people with CF, so if we can develop strategies to prevent or reduce these devastating infections, then we will reduce lung disease and enhance quality of life.

27th March update:  The airways of children with cystic fibrosis (CF) are commonly infected with a bacterium called Staphylococcus aureus. Using our CF airway model made up of human cells, we have shown that this bacterium plays an important role in making the CF lungs more vulnerable to the development nasty, lifelong lung infections. I hope to update you in full very soon.

 

We are investigating the interactions between two important pathogens in CF; Staphylococcus aureus and Pseudomonas aeruginosa. The image below shows these two bacteria on special agar plates which promote their growth.

The image on the left shows S. aureus. S. aureus appears as bright yellow/gold colonies (‘aureus’ means gold). Their ability to also use mannitol in the agar as a source of energy also causes the bacteria to have a yellow halo around it. The image on the right is an example of three different clinical isolates of P. aeruginosa obtained from people with CF. You can see from appearance alone that these bacteria are very different. Isolate 6 produces a green pigment, isolate 7 is yellow, whilst isolate 8 produces a brown pigment.

Adding bacteria to agar plates, prior to counting how many successfully bound to the surface of CF airway cells

We have gone on to examine P. aeruginosa cultures isolated from the lungs of people with CF. We have found that these different clinical isolates are very different to each other, in terms of the damaging virulence factors that they make and therefore the lung damage induced. What’s also exciting is that by mimicking disease progression, we have shown for the first time that changes to the lung environment can alter the bacteria’s ability to cause damage. Whilst some bacteria are still able to cause damage to the lungs, other isolates lose this ability.

 

Not all CF bacteria are the same. The lower image shows zones of clearance on milk agar that are clear areas indicative of enzyme (protease) activity. These enzymes are used as a defence by P. aeruginosa and may be linked to their ability to infect. The upper image shows that the enzyme is not produced by all isolates of P. aeruginosa, so this may be just one of a series of dangerous factors that we need to take into account when treating for these infections.

The ability of bacteria to migrate is important not only in developing infections, but also in being able to spread throughout the CF lung. Our research has not only showed that the clinical isolates of P. aeruginosa differ in their motility, but that changes in the environment can also influence this.

Again, not all CF bacteria are the same. The image on the left shows a clinical isolate of P. aeruginosa that can swarm across the surface of the agar plate. The image on the right is of another P. aeruginosa isolate which can is unable to migrate.

We have found that live cultures of S. aureus are able to infect our cell models of the airways. This indicates that our models are a better representation of what occurs in CF lung disease than the animal models of CF, since the animal models are not susceptible to these infections.

These experiments examined the effects of deliberate bacterial infection on our cell culture models of the airways. We used three different pathogens that are likely to be found in the airways of people with CF, these are S. aureus, P. aeruginosa and B. cepacia. Our data show that the bacteria cause more damage to the CF cell models than the healthy airways – just as these pathogens do to people with CF compared to individuals who do not have CF.

We have also looked at the responses of lung cells to bacterial infection. During an infection, airway cells release “help me signals” which are important in telling the immune system that there is an infection and specialised immune cells need to come and kill the bacteria. We have shown however that CF bacteria can breakdown these “help me signals” once they are released. This consequently protects the bacteria, preventing them from being detected and killed by the immune system.

We think that the airways of people with CF create a specific environment for pathogens, that this environment will alter the pathogens and that this further complicates the treatment of the lung infection. These data indicate that infections, in terms of the pathogens and the potential damage, are specific to the person, and the implication of this is that this could never be modelled in animals.

With the support from The Humane Research Trust, we can use our human cell models to model CF lung infections. By using bacteria taken from the lungs of people with CF, we can demonstrate how best to treat the individual infection to prevent lung damage and enhance quality of life.

Overall, all of the research done so far tells us…

  • There isn’t a “typical” CF bacteria
  • CF bacteria vary in their ability to cause damage and the environment can further influence this
  • aeruginosacan out-compete S. aureus if these infections occur simultaneously
  • aeruginosacan kill off an established S. aureus infection
  • Some CF bacteria can prevent the immune system from being able to effectively seek out and destroy them

We are currently in the process of trying to submit a research paper with these exciting findings. Hopefully we can update you with some good news regarding this very soon!

 

 

 

 

 

 

Author: admin