We assessed the effects of nutrient enrichment on three stream ecosystems running through distinct biomes (Mediterranean, Pampean and Andean). We increased the concentrations of N and P in the stream water 1.6-4-fold following a before-after control-impact paired series (BACIPS) design in each stream, and evaluated changes in the biomass of bacteria, primary producers, invertebrates and fish in the enriched (E) versus control (C) reaches after nutrient addition through a predictive-BACIPS approach. The treatment produced variable biomass responses (2-77% of explained variance) among biological communities and streams. The greatest biomass response was observed for algae in the Andean stream (77% of the variance), although fish also showed important biomass responses (about 9-48%). The strongest biomass response to enrichment (77% in all biological compartments) was found in the Andean stream. The magnitude and seasonality of biomass responses to enrichment were highly site specific, often depending on the basal nutrient concentration and on windows of ecological opportunity (periods when environmental constraints other than nutrients do not limit biomass growth). The Pampean stream, with high basal nutrient concentrations, showed a weak response to enrichment (except for invertebrates), whereas the greater responses of Andean stream communities were presumably favored by wider windows of ecological opportunity in comparison to those from the Mediterranean stream. Despite variation among sites, enrichment globally stimulated the algal-based food webs (algae and invertebrate grazers) but not the detritus-based food webs (bacteria and invertebrate shredders).Environ. Res. Lett. 8 (2013) 014002 J Artigas et al nutrient enrichment tends to globally enhance the biomass of stream biological assemblages, but that its magnitude and extent within the food web are complex and are strongly determined by environmental factors and ecosystem structure.
Background Providencia rettgeri is a nosocomial pathogen associated with urinary tract infections and related to Healthcare-Associated Infection (HAI). In recent years isolates producing New Delhi Metallo-β-lactamase (NDM) and other β-lactamases have been reported that reduce the efficiency of clinical antimicrobial treatments. In this study, we analyzed antibiotic resistance, the presence of resistance genes and the clonal relationship of two P. rettgeri isolates obtained from male patients admitted to the same hospital in Bogotá – Colombia, 2015. Results Antibiotic susceptibility profile evaluated by the Kirby-Bauer method revealed that both isolates were resistant to third-generation carbapenems and cephalosporins. Whole-genome sequencing (Illumina HiSeq) followed by SPAdes assembling, Prokka annotation in combination with an in-house Python program and resistance gene detection by ResFinder identified the same six β-lactamase genes in both isolates: blaNDM-1, blaVIM-2, blaCTX-M-15, blaOXA-10, blaCMY-2 and blaTEM-1. Additionally, various resistance genes associated with antibiotic target alteration (arnA, PmrE, PmrF, LpxA, LpxC, gyrB, folP, murA, rpoB, rpsL, tet34) were found and four efflux pumps (RosAB, EmrD, mdtH and cmlA). The additional resistance to gentamicin in one of the two isolates could be explained by a detected SNP in CpxA (Cys191Arg) which is involved in the stress response of the bacterial envelope. Genome BLAST comparison using CGView, the ANI value (99.99%) and the pangenome (using Roary) phylogenetic tree (same clade, small distance) showed high similarity between the isolates. The rMLST analysis indicated that both isolates were typed as rST-61,696, same as the RB151 isolate previously isolated in Bucaramanga, Colombia, 2013, and the FDAARGOS_330 isolate isolated in the USA, 2015. Conclusions We report the coexistence of the carbapenemase genes blaNDM-1, and blaVIM-2, together with the β-lactamase genes blaCTX-M-15, blaOXA-10, blaCMY-2 and blaTEM-1, in P. rettgeri isolates from two patients in Colombia. Whole-genome sequence analysis indicated a circulation of P. rettgeri rST-61,696 strains in America that needs to be investigated further.
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