Hidden Infection Route of Major Bacterial Pathogen Uncovered

The pattern of infection of the bacterium responsible for causing severe lung infections in people with cystic fibrosis has been uncovered by University of Liverpool's Institute of Infection and Global Health researchers. Pseudomonas aeruginosa is usually harmless to humans, but in people with cystic fibrosis (CF) or who have weakened immune systems – such as those who have had an operation or treatment for cancer – it can cause infections that are resistant to antibiotics. In CF patients in particular, infections can be impossible to eradicate from the lungs.

The team from the University made their discovery by studying the bacteria in a newly developed model, which closely reflected the human disease condition. By using this model, they showed for the first time that Pseudomonas aeruginosa colonised the nasopharynx – the part of the body which connects the back of the nose to the back of the mouth – long term and then subsequently migrated down into the lungs to cause chronic infection.

Joint first author of the study, microbiologist Dr Jo Fothergill said: "We have discovered that the nasopharynx acts as a silent reservoir for bacteria from which more serious infections in the lungs can develop."

Immunologist Dr Dan Neill, who is the other first author added: "This finding may explain why patients often suffer from recurrent infections with the same bacterial strain as continual re-infection of the lungs from the upper airways can take place."

The researchers found that Pseudomonas aeruginosa adapts while in the nasopharynx, and following this adaptation process travels to infect areas such as the lungs, which people with lung conditions find hard to prevent.

Previous studies have focused only on the lungs, so this new understanding of how the bacteria establishes infection in the upper respiratory tract prior to development of chronic lung infection provides a perfect new opportunity for more effective development of treatments at the initial site of infection.

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Professors Aras Kadioglu and Craig Winstanley were the senior authors who led the study. Professor Kadioglu said: "A better understanding of the way these bacteria colonise and adapt to the human body provides important new information about how we might prevent this process in more vulnerable people."

"It is clear that antibiotics are not an effective treatment for these infections once established in the lung, so something else needs to be developed urgently, and targeting the infection at the site of entry before chronic infection develops is one way forward."

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Source-Eurekalert