Diversity of biofilms produced by quorum-sensing-deficient clinical isolates of Pseudomonas aeruginosa

1 Department of Microbiology and Immunology, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA 2 Department of Surgery, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA 3 Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA 4 School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA Correspondence Abdul N. Hamood abdul.hamood{at}ttuhsc.edu Received 27 October 2006 Accepted 5 March 2007 The quorum-sensing (QS) systems control several virulence attributes of Pseudomonas aeruginosa . Five QS-deficient P. aeruginosa clinical isolates (CI) that were obtained from wound (CI-1), tracheal (CI-2, CI-3, CI-4) and urinary tract (CI-5) infections had previously been characterized. In this study, a flow-through continuous-culture system was utilized to examine in detail the biofilms formed by these isolates in comparison with the P. aeruginosa prototrophic strain PAO1. Analysis of the biofilms by confocal laser scanning microscopy and COMSTAT image analysis at 1 and 7 days post-inoculation showed that the isolates produced diverse biofilms. In comparison with PAO1, the CI produced biofilms that scarcely or partially covered the surface at day 1, although CI-1 produced larger microcolonies. At day 7, CI-2 and CI-4 produced mature biofilms denser than that produced by PAO1, while the biofilm formed by CI-1 changed very little from day 1. CI-1 was defective in both swarming and twitching motilities, and immunoblotting analysis confirmed that it produced a reduced level of PilA protein. The twitching-motility defect of CI-1 was not complemented by a plasmid carrying intact pilA . In the 48 h colony biofilm assay, the CI varied in susceptibility to imipenem, gentamicin and piperacillin/tazobactam. These results suggest that: (1) the isolates produced biofilms with different structures and densities from that of PAO1; (2) biofilm formation by the isolates was not influenced by either the isolation site or the QS deficiencies of the isolates; (3) the behaviour of CI-1 in the different biofilm systems may be due to its lack of swarming motility and type IV pilus-related twitching motility. Abbreviations: 3OC 12 -HSL, N -(3-oxododecanoyl) homoserine lactone; C 4 -HSL, N -butyryl homoserine lactone; CF, cystic fibrosis; CI, clinical isolate(s); max. thickness, maximum thickness; QS, quorum sensing; rc, roughness coefficient; sbr, surface-to-biovolume