Genetic and functional characterization of the gene cluster directing the biosynthesis of putisolvin I and II in Pseudomonas putida strain PCL1445

Pseudomonas putida PCL1445 secretes two cyclic lipopeptides, putisolvin I and putisolvin II, which possess a surface-tension-reducing ability, and are able to inhibit biofilm formation and to break down biofilms of Pseudomonas species including Pseudomonas aeruginosa. The putisolvin synthetase gene cluster (pso) and its surrounding region were isolated, sequenced and characterized. Three genes, termed psoA, psoB and psoC, were identified and shown to be involved in putisolvin biosynthesis. The gene products encode the 12 modules responsible for the binding of the 12 amino acids of the putisolvin peptide moiety. Sequence data indicate that the adenylation domain of the 11th module prioritizes the recognition of Val instead of Leu or Ile and consequently favours putisolvin I production over putisolvin II. Detailed analysis of the thiolation domains suggests that the first nine modules recognize the D form of the amino acid residues while the two following modules recognize the L form and the last module the L or D form, indifferently. The psoR gene, which is located upstream of psoA, shows high similarity to luxR-type regulatory genes and is required for the expression of the pso cluster. In addition, two genes, macA and macB, located downstream of psoC were identified and shown to be involved in putisolvin production or export

De betekenis van het bodemleven voor duurzame landbouw : samenvatting van presentatie "The meaning of life (in soil)"

De huidige voedselproductie is erg afhankelijk van olie. Natuurlijke processen zijn vervangen door kunstmest, gewasbeschermingsmiddelen en machinale arbeid. Dierlijke mest wordt voor een belangrijk deel geproduceerd met geïmporteerd veevoer. Dit alles loopt op olie en heeft, naast de productie van broeikasgassen, geleid tot minder bodemleven en ophoping van nutriënten (stikstof en fosfaat) in de bodem. Olie wordt schaarser en duurder. Een presentatie van Werkgroep Bodempathogenen en Bodemmicrobiologie, themadag: ‘methoden om te meten in grond’, 29 oktober 2009

Evolutionary patchwork of an insecticidal toxin shared between plant-associated pseudomonads and the insect pathogens Photorhabdus and Xenorhabdus

Background: Root-colonizing fluorescent pseudomonads are known for their excellent abilities to protect plants against soil-borne fungal pathogens. Some of these bacteria produce an insecticidal toxin (Fit) suggesting that they may exploit insect hosts as a secondary niche. However, the ecological relevance of insect toxicity and the mechanisms driving the evolution of toxin production remain puzzling. Results: Screening a large collection of plant-associated pseudomonads for insecticidal activity and presence of the Fit toxin revealed that Fit is highly indicative of insecticidal activity and predicts that Pseudomonas protegens and P. chlororaphis are exclusive Fit producers. A comparative evolutionary analysis of Fit toxin-producing Pseudomonas including the insect-pathogenic bacteria Photorhabdus and Xenorhadus, which produce the Fit related Mcf toxin, showed that fit genes are part of a dynamic genomic region with substantial presence/absence polymorphism and local variation in GC base composition. The patchy distribution and phylogenetic incongruence of fit genes indicate that the Fit cluster evolved via horizontal transfer, followed by functional integration of vertically transmitted genes, generating a unique Pseudomonas-specific insect toxin cluster. Conclusions: Our findings suggest that multiple independent evolutionary events led to formation of at least three versions of the Mcf/Fit toxin highlighting the dynamic nature of insect toxin evolution

Consequences of revised CLSI and EUCAST guidelines for antibiotic susceptibility patterns of ESBL- and AmpC β-lactamase-producing clinical Enterobacteriaceae isolates

Objectives This study aimed to: (i) analyse the antibiotic susceptibility testing (AST) profiles of extended spectrum β-lactamase (ESBL)- and AmpC β-lactamase-producing clinical Enterobacteriaceae isolates applying EUCAST 2013 AST guidelines; and (ii) evaluate discrepancies in AST profiles according to EUCAST 2010 guidelines, EUCAST 2013 guidelines, CLSI 2009 guidelines and CLSI 2013 guidelines. Methods The 195 ESBL- and/or AmpC β-lactamase-producing Enterobacteriaceae isolates used in this study were systematically characterized by disc diffusion AST interpreted according to the 2013 guidelines of EUCAST and CLSI, the EUCAST 2010 guidelines and the CLSI 2009 guidelines. Results Individual cephalosporin AST patterns according to EUCAST 2013 guidelines were described for individual ESBL and AmpC β-lactamase genotypes. Significant differences in the susceptibility rates of important cephalosporins such as cefepime, ceftazidime and cefotaxime applying EUCAST 2013 and CLSI 2013 AST guidelines were demonstrated for ESBL- and AmpC β-lactamase-producing isolates. Conclusions The confirmation of ESBL and/or AmpC β-lactamase production can support the selection of an adequate antibiotic drug therapy. Despite a harmonized CLSI and EUCAST ‘report as found' strategy for cephalosporins and ESBL-producing isolates, AST interpretation according to the CLSI 2013 and EUCAST 2013 guidelines shows significant differences in susceptibility rates for mainstay cephalosporins such as cefepime, ceftazidime and cefotaxime. Thus, further harmonization of clinical breakpoints is warrante

Effects of clinical breakpoint changes in CLSI guidelines 2010/2011 and EUCAST guidelines 2011 on antibiotic susceptibility test reporting of Gram-negative bacilli

Objectives The aim of this study was to analyse the effects of clinical breakpoint changes in CLSI 2010 and 2011 guidelines and EUCAST 2011 guidelines on antibiotic susceptibility testing (AST) reports. Methods In total, 3713 non-duplicate clinical isolates of Enterobacteriaceae, Pseudomonas aeruginosa, Stenotrophomonas maltophilia and Acinetobacter baumannii were analysed. Inhibition zone diameters were determined for β-lactams, carbapenems, fluoroquinolones, aminoglycosides and trimethoprim/sulfamethoxazole. CLSI 2009-11 and EUCAST 2011 clinical breakpoints were applied. Results Changes in resistance as defined per the guidelines affected individual species and drug classes differently. The cefepime resistance rate in Escherichia coli and Enterobacter cloacae increased from 2.1% and 1.3% to 8.2% and 6.9%, respectively, applying CLSI 2009-11 versus EUCAST 2011 guidelines. Ertapenem resistance rates in E. cloacae increased from 2.6% with CLSI 2009 to 7.2% for CLSI 2010 and 2011, and to 10.1% when applying EUCAST 2011. Cefepime and meropenem resistance rates in P. aeruginosa increased from 12.2% and 20.6% to 19.8% and 27.7%, respectively, comparing CLSI 2009-11 with EUCAST 2011. Tobramycin and gentamicin resistance rates in A. baumannii increased from 15.9% and 25.4% to 34.9% and 44.4% applying CLSI 2009-11 versus EUCAST 2011. Conclusions Higher resistance rates reported due to breakpoint changes in CLSI and EUCAST guidelines will result in increasing numbers of Gram-negative bacilli reported as multidrug resistant. AST reports classifying amoxicillin/clavulanic acid, cefepime or carbapenem resistance will lead clinicians to use alternative agents. Upon implementation of the EUCAST guidelines, laboratories should be aware of the implications of modified drug susceptibility testing reports on antibiotic prescription policie