Cell-associated hemolysis activity in the clinical strain of Pseudomonas fluorescens MFN1032

<p>Abstract</p> <p>Background</p> <p>MFN1032 is a clinical <it>Pseudomonas fluorescens </it>strain able to grow at 37°C. MFN1032 cells induce necrosis and apoptosis in rat glial cells at this temperature. This strain displays secretion-mediated hemolytic activity involving phospholipase C and cyclolipopeptides. Under laboratory conditions, this activity is not expressed at 37°C. This activity is tightly regulated and is subject to phase variation.</p> <p>Results</p> <p>We found that MFN1032 displays a cell-associated hemolytic activity distinct from the secreted hemolytic activity. Cell-associated hemolysis was expressed at 37°C and was only detected <it>in vitro </it>in mid log growth phase in the presence of erythrocytes. We studied the regulation of this activity in the wild-type strain and in a mutant defective in the Gac two-component pathway. GacS/GacA is a negative regulator of this activity. In contrast to the <it>Pseudomonas fluorescens </it>strains PfO-1 and Pf5, whose genomes have been sequenced, the MFN1032 strain has the type III secretion-like genes <it>hrc</it>RST belonging to the <it>hrpU </it>operon. We showed that disruption of this operon abolished cell-associated hemolytic activity. This activity was not detected in <it>P.fluorescens </it>strains carrying similar <it>hrc </it>genes, as for the <it>P. fluorescens </it>psychrotrophic strain MF37.</p> <p>Conclusions</p> <p>To our knowledge this the first demonstration of cell-associated hemolytic activity of a clinical strain of <it>Pseudomonas fluorescens</it>. Moreover, this activity seems to be related to a functional <it>hrpU </it>operon and is independent of biosurfactant production. Precise link between a functional <it>hrpU </it>operon and cell-associated hemolytic activity remains to be elucidated.</p

Involvement of a phospholipase C in the hemolytic activity of a clinical strain of Pseudomonas fluorescens

<p>Abstract</p> <p>Background</p> <p><it>Pseudomonas fluorescens </it>is a ubiquitous Gram-negative bacterium frequently encountered in hospitals as a contaminant of injectable material and surfaces. This psychrotrophic bacterium, commonly described as unable to grow at temperatures above 32°C, is now considered non pathogenic. We studied a recently identified clinical strain of <it>P. fluorescens </it>biovar I, MFN1032, which is considered to cause human lung infection and can grow at 37°C in laboratory conditions.</p> <p>Results</p> <p>We found that MFN1032 secreted extracellular factors with a lytic potential at least as high as that of MF37, a psychrotrophic strain of <it>P. fluorescens </it>or the mesophilic opportunistic pathogen, <it>Pseudomonas aeruginosa </it>PAO1. We demonstrated the direct, and indirect – through increases in biosurfactant release – involvement of a phospholipase C in the hemolytic activity of this bacterium. Sequence analysis assigned this phospholipase C to a new group of phospholipases C different from those produced by <it>P. aeruginosa</it>. We show that changes in PlcC production have pleiotropic effects and that <it>plcC </it>overexpression and <it>plcC </it>extinction increase MFN1032 toxicity and colonization, respectively.</p> <p>Conclusion</p> <p>This study provides the first demonstration that a PLC is involved in the secreted hemolytic activity of a clinical strain of <it>Pseudomonas fluorescens</it>. Moreover, this phospholipase C seems to belong to a complex biological network associated with the biosurfactant production.</p

Tumeurs de la conjonctive bulbaire (étude rétrospective sur 117 lésions)

LYON1-BU Santé (693882101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Phenotypic variation in the Pseudomonas fluorescens clinical strain MFN1032

International audiencePseudomonas fluorescens is a highly heterogeneous species and includes both avirulent strains and clinical strains involved in nosocomial infections. We previously demonstrated that clinical strain MFN1032 has hemolytic activity involving phospholipase C (PlcC) and biosurfactants (BSs), similar to that of the opportunistic pathogen Pseudomonas aeruginosa. When incubated under specific conditions, MFN1032 forms translucent phenotypic variant colonies defective in hemolysis, but not necessarily in PlcC. We analyzed eight variants of the original strain MFN1032 and found that they clustered into two groups. Mutations of genes encoding the two-component regulatory system GacS/GacA are responsible for phenotypic variation in the first group of variants. These group 1 variants did not produce secondary metabolites and had impaired biofilm formation. The second group was composed of hyperflagellated cells with enhanced biofilm capacity: they did not produce BSs and were thus unable to swarm. Artificial reduction of the intracellular level of c-di-GMP restored the ability to form biofilm to levels shown by the wild type, but production of BSs was still repressed. Phenotypic variation might increase the virulence potential of this strain