55 Investigation of the RetS–GacAS regulatory network in clinical Pseudomonas aeruginosa isolates reveals evolutionary adaptation

• DOI: 10.1016/s1569-1993(14)60192-2
• Publication Date: 2014-06-03T08:51:43Z
• Authors: M. Lindegaard; R.L. Marvig; C. Lassek; D. Zühlke; K. Riedel; S. Molin; H.K. Johansen; K. Long
• Keywords: Pulmonary and Respiratory Medicine; 0301 basic medicine; 03 medical and health sciences; Pediatrics, Perinatology, and Child Health; 3. Good health

Objective: Burkholderia cenocepacia (Bc) is a highly antimicrobially resistant pathogen, which is rarely eradicated from cystic fibrosis (CF) patients. While Bc is generally confined to the lung, bacteraemia can develop in a subgroup of patients contributing to a sharp decline in health. How Bc chronically colonises and causes bacteraemia remain poorly understood. Bacteria can change phenotype during infection, adapting to the host environment. We aim to identify the alterations in Bc phenotype from initial colonisation to chronic infection. Methods: A series of genetically identical sequential Bc isolates from two siblings with CF, one with chronic infection confined to the lung (Pt1), the other with bacteraemia (Pt2), were studied. In vivo virulence using Galleria mellonella, mucoidy on yeast extract mannitol (YEM) agar and adhesion to CF lung epithelial cells (CFBE41o−) were examined. Results: All isolates were relatively avirulent in vivo in Galleria mellonella. The blood isolates from Pt2 were considerably more virulent than a sputum isolate from that patient (P = 0.014). Mucoid production by Bc has been associated with better patient outcomes; however, all but one isolate were non-mucoid on YEM. Both sputum and blood isolates increased attachment to CFBEs over time of colonisation (p< 0.005 and 0.001 respectively), indicating an increased potential for host epithelial interactions over time. This key adaptation was confirmed by confocal microscopy. We are currently comparing the proteomes of all isolates to identify alterations in protein expression that may be involved. Conclusions: It is clear that Bc adapts and increases virulence during colonisation.