Simultaneous production of rhamnolipids, 2-alkyl-4-hydroxyquinolines, and phenazines by clinical isolates of Pseudomonas aeruginosa

Effect of lipid and fatty acid composition of phospholipid vesicles on long-term stability and their response to Staphylococcus aureus and Pseudomonas aeruginosa supernatants

Phospholipid vesicles have been the focus of attention as potential vehicles for drug delivery, as they are biomimetic, easy to produce, and contain an aqueous compartment which can be used to carry hydrophilic material, such as drugs or dyes. Lipid vesicles used for this purpose present a particular challenge, as they are not especially stable and can rapidly break down and release their contents away from the target area, especially at physiological temperatures/environments. This study aims to investigate optimum methods for vesicle stabilization where the vesicles are employed as part of a system or technology that signals the presence of pathogenic bacteria via the effect of secreted cytolytic virulence factors on a sensor interface. A number of approaches have been investigated and are presented here as a systematic study of the long-term (14 day) stability at 37 °C, and at various pHs. The response of vesicles, both in suspension and within hydrogels, to Staphylococcus aureus (RN 4282) and Pseudomonas aeruginosa (PAO1) whole bacteria, and supernatants from overnight cultures of both (containing secreted proteins but free of cells), was measured via a sensitive encapsulated carboxyfluorescein release assay. The results showed that lipid chain length, cholesterol concentration, and stabilization via photopolymer stable components were critical in achieving stability. Finally, dispersion of the optimum vesicle formulation in hydrogel matrixes was investigated, culminating in the in vivo demonstration of a simple prototype wound dressing.

The Burkholderia cenocepacia K56-2 pleiotropic regulator Pbr, is required for stress resistance and virulence

Burkholderia cenocepacia is one of the most virulent species of the Burkholderia cepacia complex, a group of bacteria that emerged as important pathogens, especially to cystic fibrosis (CF) patients. In this study, we report the identification and characterization of a mutant strain derived form the CF isolate Burkholderia cenocepacia K56-2, carrying a plasposon insertion in a gene, located in a 3516 bp chromosomal region with an atypical G+C content, encoding a 80 amino acid putative regulatory protein named Pbr. Besides its inability to produce phenazines, the B. cenocepacia K56-2 pbr mutant exhibited a pleiotropic phenotype, including impaired survival to oxidative and osmotic stress, aromatic amino acid and prolonged nutrient starvation periods. In addition, the pbr mutant exhibited decreased virulence the nematode Caenorhabditis elegans. Altogether, our results demonstrate the involvement of Pbr on the regulation of phenazine biosynthesis, and an important role for this regulatory protein on several cellular processes related to stress resistance and virulence.

Rhamnolipid-induced shedding of flagellin from Pseudomonas aeruginosa provokes hBD-2 and IL-8 response in human keratinocytes

Several 'pathogen-associated molecular pattern' (PAMP) of the opportunistic pathogen Pseudomonas aeruginosa activate the innate immune system in epithelial cells. Particularly the production of antimicrobial peptides such as the human beta-defensin-2 (hBD-2) and proinflammatory cytokines as the interleukin (IL)-8 is boosted. In the present study culture supernatants of static grown P. aeruginosa were found to be potent hBD-2 and IL-8 inducers, indicating a soluble or shedded PAMP, comparable to that of heat-killed bacterial supernatants. In subsequent analyses this PAMP was identified as flagellin, the major structural protein of the flagella. Flagellin is known to be an immunostimulatory potent factor, but the mechanisms by which P. aeruginosa is able to remove flagellin from the flagella remain unknown. Here we provide evidence for the presence of a factor responsible for release of flagellin from the flagella. Purification of this factor and subsequent mass spectrometry analyses identified rhamnolipids as responsible agents. Our findings indicate that maybe upon adhesion to surfaces P. aeruginosa alters the outer membrane composition in a rhamnolipid-depending manner, thereby shedding flagellin from the flagella. In turn epithelial cells recognize flagellin and cause the synthesis of antimicrobial peptides as well as recruitment of inflammatory cells by induction of proinflammatory cytokines.