Abstract: The searches identified two multicentre, randomized, double-blind controlled clinical trials eligible for inclusion in the review with a total of 78 participants (adults and children); one trial was done in people who were clinically stable, the other in people experiencing pulmonary exacerbations. These trials prospectively assessed whether the use of biofilm antimicrobial susceptibility testing improved microbiological and clinical outcomes in participants with cystic fibrosis who were infected with Pseudomonas aeruginosa. The primary outcome was the change in sputum Pseudomonas aeruginosa density from the beginning to the end of antibiotic therapy. Although the intervention was shown to be safe, the data from these two trials did not provide evidence that biofilm susceptibility testing was superior to conventional susceptibility testing either in terms of microbiological or lung function outcomes. One of the trials also measured risk and time to subsequent exacerbation as well as quality of life measures and did not demonstrate any difference between groups in these outcomes. Both trials had an overall low risk of bias and the quality of the evidence using GRADE criteria was deemed to be moderate to high for the outcomes selected. The current evidence is insufficient to recommend choosing antibiotics based on biofilm antimicrobial susceptibility testing rather than conventional antimicrobial susceptibility testing in the treatment of Pseudomonas aeruginosa pulmonary infections in people with cystic fibrosis. Biofilm antimicrobial susceptibility testing may be more appropriate in the development of newer, more effective formulations of drugs which can then be tested in clinical trials.

Plain-language summary: We included two trials, one run in the USA (in people who were clinically stable) and one run in Canada (in people who were having an exacerbation or respiratory flare up). A total of 78 people from these trials gave sputum samples. Bacteria from these samples were grown in either a liquid (34 samples) or biofilm (44 samples) with an equal chance of being grown in either one. Neither the individuals or their clinicians knew before or during the trial which method had been used for the sample from each person. A mixture of adults and children took part in the trials, with the average age being around 20 to 30 years. There were an equal number of men and women in both trials. Around half the people in the trials had two copies of the delta F508 gene and there were almost equal number of these in each group. Average lung function in both groups was similar. The main outcome of both trials was the decrease in the amount of bacteria in the sputum of people in each group after antibiotic treatment. There was no difference in the levels of bacteria found in the sputum or in the improvement in lung function between the two groups in either trial. In both trials, there was a similar number of individuals in each group who had either a mild or moderate side effect. There were no serious side effects reported by anyone in either study. The evidence does not show that one method of testing is better than the other and that people receiving antibiotics chosen on the basis of either method have equal chances of any side effects. The quality of the evidence was quite good as people had equal chances of being in either group and they did not know which testing group they were in. This means we don't think the trial results would have been affected because of this.