Hello my name is Thomas Bjarnsholt and I am professor in Chronic infections and Biofilms at the University of Copenhagen. Today I will introduce you to the chronic lung infection in patients with cystic fibrosis The chronic lung infection of patients suffering from the inherited disorder Cystic fibrosis or CF is the classical example of chronic infections and probably the most studied biofilm infection. Much of our biofilm knowledge is derived from this disease and the majority of scientific articles always relates back to cystic fibrosis even though other chronic infections are being investigated with increasing effort. CF is the most common lethal inherited disease in Caucasians with a worldwide incidence of gene defects in the range of 1:32,000 to 1:2,000 live births. It affects many organs but the lung infection is the most severe . The genetic cause of CF was identified in 1989 as a defect in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene, which is located on chromosome 7. The CFTR defect causes a decrease in chloride secretion and an increase in sodium absorption. In the CF lung, this results in dehydrated viscous mucus that is very difficult to clear mechanically, i.e., by coughing. This abnormal viscous mucus is the perfect hiding place for bacteria, and is the cause of the chronic lung infection. Healthy people also produce mucus but here it can be transported out and do not get stuck in the lungs. Pseudomonas aeruginosa is the most common and important bacterium in the CF lung. Since 1976, CF patients at the Copenhagen CF Centre suffering from chronic P. aeruginosa lung infection have successfully received intensive treatment with high concentrations of antibiotics . This treatment is referred to as maintenance treatment and chronic suppressive treatment. Before 1976, only 50% of CF patients would survive five years of chronic P. aeruginosa lung infection. Most CF patients today survive for decades with chronic P. aeruginosa infections. Despite the aggressive and intensive treatment of chronic P. aeruginosa infections, the bacteria still persist in the CF lung. A few years ago we made a study where we compared lung samples from CF patients before and after the chronic suppressive treatment was introduced in Copenhagen. We included 12 autopsies from deceased short term infected CF patients; these were obtained prior to initiation of the present aggressive antibiotic treatment (1975-78). These patients were chronic infected for an average of 3.5 years before death. The other group was 3 explanted lungs from present long term P. aeruginosa infected CF patients . They had i.v. antibiotics every 3rd month since 1976 plus inhalation of colistin daily since 1987. This group had been chronic infected for 28 years on average and had a double sided lung transplantation why we could get the old lungs. In the study we observed where in the lungs we could find bacteria both planktonic and biofilms. In general the human lung can be divided into a conductive zone and a respiratory zone. The conductive zone is the upper part of the lung and serves to transport the inhaled and exhaled air back and forth to the respiratory zone where the gas exchange takes place. This is where the blood is oxygenated and the CO2 and CO is removed. We used some specific staining’s to stain the bacteria red and the human cells blue. As can be seen from these pictures in both groups of samples bacteria in biofilms were present in the conductive zone of the lungs. The reason why the “before” pictures are less bright is due to the age of the samples. The red is the bacteria and the blue cells are the white blood cells. As it can be seen a waste amount of white blood cells actually are present surrounding the bacteria. The only difference we could detect was the untreated group had more tissue destruction than the aggressive treated patients. In the pre-treatment samples it was difficult to find intact tissue, it was all a big mess. In the aggressive treatment samples tissue destruction could also be found but the airways were more intact and even the small cilia hairs can be seen in this picture. These are the small hairs which normally transport the mucus up in healthy individuals. You have probably all experienced pneumonia coughing up green and yellow phlegm this is the mucus with encapsulated bacteria or viruses together with the inflammatory cells. It is a normal mechanism to clear the lungs, also from inhaled dust articles etc. The interesting part of the study was when we examined the respiratory zone of both sets of samples. In the “before” group, the group not receiving the aggressive therapy we could find bacteria in the respiratory zone but strikingly only very few bacteria in the respiratory zone of the “post” patients, the patients receiving the aggressive treatment. Again we could also detect much more tissue destruction in the pre group. This indicates to us that before the aggressive antibiotic therapy P. aeruginosa infected and destroyed the CF lung due to fast spreading, into the respiratory zone. The aggressive maintenance treatment suppresses but cannot eradicate the bacteria from the conductive zone, whereas the remaining respiratory zone is protected from massive biofilm infection, for prolonged time. The conductive zone serves as a reservoir; here the bacteria are organized in biofilms embedded in puss and mucus, a trait which is independent on the time course of the infection and amounts of antibiotics. Interestingly we found no bacteria adhering to the epithelial tissue; the biofilms were all imbedded in the puss/mucus and was surrounded by white blood cells. So in conclusion P. aeruginosa persists in the CF lung, despite of aggressive antibiotic treatment and the many white blood cells, due to its ability to form biofilms. Within these biofilms the bacteria are protected against antibiotics and the host defence.
