Preliminary data on antibacterial activity of Echinacea purpurea-associated bacterial communities against Burkholderia cepacia complex strains, opportunistic pathogens of Cystic Fibrosis patients.

Burkholderia cepacia complex bacteria (Bcc) represent a serious threat for immune-compromised patient affected by Cystic Fibrosis (CF) since they are resistant to many substances and to most antibiotics. For this reason, the research of new natural compounds able to inhibit the growth of Bcc strains has raised new interest during the last years. A source of such natural compounds is represented by medicinal plants and, in particular, by bacterial communities associated with these plants able to produce molecules with antimicrobial activity. In this work, a panel of 151 (endophytic) bacteria isolated from three different compartments (rhizospheric soil, roots, and stem/leaves) of the medicinal plant Echinacea purpurea were tested (using the cross-streak method) for their ability to inhibit the growth of 10 Bcc strains. Data obtained revealed that bacteria isolated from the roots of E. purpurea are the most active in the inhibition of Bcc strains, followed by bacteria isolated from the rhizospheric soil, and endophytes from stem/leaf compartment. At the same time, Bcc strains of environmental origin showed a higher resistance toward inhibition than the Bcc strains with clinical (i.e. CF patients) origin. Differences in the inhibition activity of E. purpurea-associated bacteria are mainly linked to the environment -the plant compartment- rather than to their taxonomical position.

Two type IV secretion systems with different functions in Burkholderia cenocepacia K56-2.

Bacterial type IV secretion systems (T4SS) perform two fundamental functions related to pathogenesis: the delivery of effector molecules to eukaryotic target cells, and genetic exchange. Two T4SSs have been identified in Burkholderia cenocepacia K56-2, a representative of the ET12 lineage of the B. cepacia complex (Bcc). The plant tissue watersoaking (Ptw) T4SS encoded on a resident 92 kb plasmid is a chimera composed of VirB/D4 and F-specific subunits, and is responsible for the translocation of effector(s) that have been linked to the Ptw phenotype. The bc-VirB/D4 system located on chromosome II displays homology to the VirB/D4 T4SS of Agrobacterium tumefaciens. In contrast to the Ptw T4SS, the bc-VirB/D4 T4SS was found to be dispensable for Ptw effector(s) secretion, but was found to be involved in plasmid mobilization. The fertility inhibitor Osa did not affect the secretion of Ptw effector(s) via the Ptw system, but did disrupt the mobilization of a RSF1010 derivative plasmid.

Burkholderia cenocepacia J2315 acyl carrier protein: a potential target for antimicrobials' development?

This work describes the isolation and characterization of an acyl carrier protein (ACP) mutant from Burkholderia cenocepacia J2315, a strain of the Burkholderia cepacia complex (Bcc). Bcc comprises at least 9 species that emerged as opportunistic pathogens able to cause life-threatening infections, particularly severe among cystic fibrosis patients. Bacterial ACPs are the donors of the acyl moiety involved in the biosynthesis of fatty acids, which play a central role in metabolism. The mutant was found to exhibit an increased ability to form biofilms in vitro, a more hydrophobic cell surface and reduced ability to colonize and kill the nematode Caenorhabditis elegans, used as a model of infection. The B. cenocepacia J2315 ACP protein is composed of 79 amino acid residues, with a predicted molecular mass and pI of 8.71kDa and 4.08, respectively. The ACP amino acid sequence was found to be 100% conserved within the genomes of the 52 Burkholderia strains sequenced so far. These data, together with results showing that the predicted structure of B. cenocepacia J2315 ACP is remarkably similar to the Escherichia coli AcpP, highlight its potential as a target to develop antibacterial agents to combat infections caused not only by Bcc species, but also by other Burkholderia species, especially B. pseudomallei and B. mallei.