Population Structure of Pseudomonas aeruginosa from Five Mediterranean Countries: Evidence for Frequent Recombination and Epidemic Occurrence of CC235

Several studies in recent years have provided evidence that Pseudomonas aeruginosa has a non-clonal population structure punctuated by highly successful epidemic clones or clonal complexes. The role of recombination in the diversification of P. aeruginosa clones has been suggested, but not yet demonstrated using multi-locus sequence typing (MLST). Isolates of P. aeruginosa from five Mediterranean countries (n = 141) were subjected to pulsed-field gel electrophoresis (PFGE), serotyping and PCR targeting the virulence genes exoS and exoU. The occurrence of multi-resistance (≥3 antipseudomonal drugs) was analyzed with disk diffusion according to EUCAST. MLST was performed on a subset of strains (n = 110) most of them had a distinct PFGE variant. MLST data were analyzed with Bionumerics 6.0, using minimal spanning tree (MST) as well as eBURST. Measurement of clonality was assessed by the standardized index of association (IAS). Evidence of recombination was estimated by ClonalFrame as well as SplitsTree4.0. The MST analysis connected 70 sequence types, among which ST235 was by far the most common. ST235 was very frequently associated with the O11 serotype, and frequently displayed multi-resistance and the virulence genotype exoS−/exoU+. ClonalFrame linked several groups previously identified by eBURST and MST, and provided insight to the evolutionary events occurring in the population; the recombination/mutation ratio was found to be 8.4. A Neighbor-Net analysis based on the concatenated sequences revealed a complex network, providing evidence of frequent recombination. The index of association when all the strains were considered indicated a freely recombining population. P. aeruginosa isolates from the Mediterranean countries display an epidemic population structure, particularly dominated by ST235-O11, which has earlier also been coupled to the spread of ß-lactamases in many countries

Dissemination of bla(VIM) in Greece at the peak of the epidemic of 2005-2006: clonal expansion of Klebsiella pneumoniae clonal complex 147

VIM-producing Klebsiella pneumoniae (n=21) isolated from ten Greek hospitals during 2003-2007 were characterized with multilocus sequence typing (MLST), semi-automated repetitive sequence-based PCR (rep-PCR) (Diversilab), plasmid replicon typing, serotyping and screening for multiple resistance determinants. The isolates were selected to represent different strain clusters (defined by >80% similarity) according to pulsed-field gel electrophoresis. MLST identified three major clonal complexes (CCs); CC147 (n=8), CC18 (n=5) and CC14 (n=3). Plasmid replicon typing showed that IncA/C and/or IncFII(K) replicons were detected among isolates in each of the major CCs. Good concordance was observed between semi-automated-rep PCR genotyping and MLST

Physiological responses and fruit quality of four peach cultivars under sustained and cyclic deficit irrigation in center-west of Tunisia

In arid and semi-arid regions, the research and application of new irrigation techniques that economize water without altering tree performance and fruit quality is a challenge. The aim of this study was to investigate the effect of two different deficit irrigation strategies on tree physiology and fruit quality of four Prunus persica cultivars: two early-ripening cultivars (Flordastar and Early Maycrest), a mid-season cultivar (Rubirich), and a late-ripening cultivar (O'Henry). During two consecutive seasons (2016 and 2017), three different irrigation treatments were established: i) Full Irrigation (FI; 100% ET c ), ii) Sustained Deficit Irrigation (SDI; 50% ET c ) and iii) Cyclic Deficit Irrigation (CDI; trees irrigated at 100% field capacity whenever the soil moisture dropped to 50% field capacity). Tree water status, gas exchange, yield, fruit pomology and the concentrations of the main sugars and organic acids were determined. Deficit irrigation decreased net photosynthesis rate, stomatal conductance and transpiration rate while it improved instantaneous water use efficiency (WUEins). In O'Henry cultivar, WUEins increased from 3.21 μ mol mmol –1 in FI to 7.04 μmol mmol –1 in CDI during harvest. Deficit irrigation significantly reduced shoot growth in the four cultivars. Furthermore, SDI decreased the yield significantly (from 41 to 26.3 kg in O'Henry cultivar during 2016), fruit size and weight while CDI increased soluble solids and sugar contents and decreased titratable acidity. The total sugar content increased significantly under deficit irrigation in all cultivars studied. In conclusion, CDI seems to be the best strategy in semi-arid regions, since it can save water and improve fruit quality parameters