University Of Iowa Researchers Develop Test Indicating Cystic Fibrosis Lungs Are Infected With Bacterial Biofilms

Infection by the bacterium Pseudomonas aeruginosa (P. aeruginosa) is the main cause of death in patients with CF. The Pseudomonas is able to set up permanent residence in the lungs of patients with CF where it is impossible to kill, even with powerful antibiotic treatment. In addition, CF patients’ own immune systems seem to overreact to the bacteria, damaging tissue and eventually destroying the lungs.

"This high level of antibiotic resistance and a host immune response that does more harm than good are the hallmarks of a bacterial biofilm," said E. Peter Greenberg, Ph.D., Virgil L. and Evalyn Shepperd Endowed Professor of Molecular Pathogenisis and UI professor of microbiology. He is an author of a study that appears in the October 12 issue of the journal Nature.

Biofilms are organized communities of bacterial cells encased in a self-produced slime. The bacterial cells produce signaling molecules, also called quorum-sensing molecules, that allow the cells to communicate with each other. At a critical cell density, these signals have accumulated and trigger the expression of a specific set of genes, which results in the formation of the biofilm. By growing as a biofilm, bacteria can survive and thrive in hostile environments.

Although the P. aeruginosa isolated from the lungs of CF patients looks like a biofilm and acts like a biofilm, until now there has not been an objective test available to confirm that it is a biofilm. The researchers also did not know what proportion of the P. aeruginosa might be in a biofilm in the lung.

"We needed a way to show that the Pseudomonas in CF lungs was communicating like a biofilm. That could tell us about the Pseudomonas lifestyle," said Pradeep Singh, M.D., UI assistant professor of internal medicine and a lead author on the study.

Greenberg and his colleagues have spent much of the last decade studying the inner workings of biofilms. They discovered that P. aeruginosa uses one of two particular quorum-sensing molecules to initiate the formation of biofilms. In November 1999, the researchers screened the entire bacterial genome, identifying 39 genes that are strongly controlled by the quorum-sensing system.

In this latest study, Greenberg, Singh and their colleagues have developed a sensitive new test which shows that Pseudomonas from CF lungs produce the telltale, quorum-sensing molecules that are the signals for biofilm formation.

"The fact that the P. aeruginosa in CF lung sputum are making the signals in the ratios that we see tells us that there is a biofilm and that most of the P. aeruginosa in th