The current pathogenic theory of spontaneous bacterial peritonitis (SBP) in patients with cirrhosis and ascites suggests that repeated episodes of bacterial translocation (BT) from intestinal lumen to mesenteric lymph nodes followed by systemic seeding are the key steps for the final development of infectious events. However, most of the episodes of systemic bacterial circulation remain undetected. Therefore, we investigated the hypothetical presence of bacteria in blood and/or ascitic fluid (AF) from patients with cirrhosis and sterile (culture negative) AF by means of bacterial DNA (bactDNA) detection and identification. Twenty-eight consecutively admitted patients with cirrhosis and presence of AF were included in the study. BactDNA was detected using a polymerase chain reaction (PCR)-based method. The corresponding bacteria were identified by nucleotide sequencing of purified PCR products. BactDNA was detected simultaneously in blood and AF in 9 patients (32.1%). DNA sequencing allowed the identification of Escherichia coli (n ‫؍‬ 7) and Staphylococcus aureus (n ‫؍‬ 2). In all cases, the similarity between the sequence found in AF and blood indicated that the bactDNA present in both locations originated from a single clone (single translocation event). Child-Pugh score and basic hemodynamic, clinical, endoscopic, and biochemical characteristics were similar among patients with or without the presence of bactDNA. In conclusion, we have detected bactDNA in serum and AF in 32% of all patients studied, and this likely represents single clone episodes of translocation and systemic seeding. E. coli is the most frequently identified bacteria. (HEPATOLOGY 2002;36:135-141.)

No abstract

Arsenate [As(V); HAsO 42؊ ] respiration by bacteria is poorly understood at the molecular level largely due to a paucity of genetically tractable organisms with this metabolic capability. We report here the isolation of a new As(V)-respiring strain (ANA-3) that is phylogenetically related to members of the genus Shewanella and that also provides a useful model system with which to explore the molecular basis of As(V) respiration. This gram-negative strain stoichiometrically couples the oxidation of lactate to acetate with the reduction of As(V) to arsenite [As(III); HAsO 2 ]. The generation time and lactate molar growth yield (Y lactate ) are 2.8 h and 10.0 g of cells mol of lactate ؊1 , respectively, when it is grown anaerobically on lactate and As(V). ANA-3 uses a wide variety of terminal electron acceptors, including oxygen, soluble ferric iron, oxides of iron and manganese, nitrate, fumarate, the humic acid functional analog 2,6-anthraquinone disulfonate, and thiosulfate. ANA-3 also reduces As(V) to As(III) in the presence of oxygen and resists high concentrations of As(III) (up to 10 mM) when grown under either aerobic or anaerobic conditions. ANA-3 possesses an ars operon (arsDABC) that allows it to resist high levels of As(III); this operon also confers resistance to the As-sensitive strains Shewanella oneidensis MR-1 and Escherichia coli AW3110. When the gene encoding the As(III) efflux pump, arsB, is inactivated in ANA-3 by a polar mutation that also eliminates the expression of arsC, which encodes an As(V) reductase, the resulting As(III)-sensitive strain still respires As(V); however, the generation time and the Y lactate value are two-and threefold lower, respectively, than those of the wild type. These results suggest that ArsB and ArsC may be useful for As(V)-respiring bacteria in environments where As concentrations are high, but that neither is required for respiration.The contamination of groundwaters and surface waters with arsenic (As) is a major concern to public health in countries such as Bangladesh, China, Taiwan, Argentina, Chile, and the United States (40). Elevated As concentrations typically derive from the weathering of As-bearing minerals and/or from geothermal sources (2, 58). It is now known that a variety of microorganisms, including members of the Eukarya, Archaea, and Bacteria, influence As geochemistry in many locales throughout the world by virtue of their metabolism (31,35,53). These metabolic processes include oxidation (49, 58), reduction (1, 13), and methylation reactions (5) that strongly affect (and in some cases, control) As speciation in the environment. One process that is particularly intriguing is microbial respiration of arsenate [As(V); HAsO 4 Ϫ2 ]. In the absence of oxygen, microorganisms can gain energy by coupling the oxidation of organic material to As(V) reduction, resulting in the production of the highly toxic As compound, arsenite [As(III); HAsO 2 ]. As(V)-respiring organisms can affect water quality by catalyzing the mobilization of As(III) from sediments...

The diversity of microorganisms present in a sediment colonized by the phanerogam Zostera noltii has been analyzed. Microbial DNA was extracted and used for constructing two 16S rDNA clone libraries for Bacteria and Archaea. Bacterial diversity was very high in these samples, since 57 different sequences were found among the 60 clones analyzed. Eight major lineages of the Domain Bacteria were represented in the library. The most frequently retrieved bacterial group (36% of the clones) was ␦-Proteobacteria related to sulfate-reducing bacteria. The second most abundant group (27%) was ␥-Proteobacteria, including five clones closely related to S-oxidizing endosymbionts. The archaeal clone library included members of Crenarchaeota and Euryarchaeota, with nine different sequences among the 15 analyzed clones, indicating less diversity when compared to the Bacteria organisms. None of these sequences was closely related to cultured Archaea organisms.Our objective in this study was to describe the diversity of the prokaryotic community inhabiting a marine sediment colonized by the marine phanerogam Zostera noltii located in the Bassin d'Arcachon, South-West France. This is a macrotidal coastal lagoon that represents the most extensive intertidal meadows of this rooted phanerogam in Western Europe (70 km 2 ). This seagrass ecosystem is characterized by a high iron content, 111.5 (dry weight) g/g (32) in the sediment, as well as strong tidal activity, which ensures regular mixing of the water body and exposes the sediment surface to the air for between 4 and 8 h each day. This environment is different from those that have previously been studied by molecular methods due to the presence of Z. noltii roots and rhizomes. A number of recent studies have shown that living seagrasses release dissolved organic carbon, which can significantly influence the composition and activity of the seagrass rhizosphere microflora (24, 36). For example, several studies have demonstrated high rates of heterotrophic nitrogen fixation in the rhizosphere of Z. noltii-colonized sediments which are coupled to the photosynthetic activity of the plants via the release of fixed carbon from the roots (20,24,36). Similarly, substantial stimulation of sulfate reduction rates in seagrass-colonized sediments in the light have been reported (4,25). These data indicate a close interaction between the plants and the microbial community in the rhizosphere.Samples. Z. noltii-colonized sediment cores (5-cm diameter) were collected from Station A in the Bassin d'Arcachon in July 1996 and kept in the dark at Ϫ20°C until processed. Station A is located in the center of the Bay, in an open zone subjected to marine influences. Sediment cores that contained extensive rhizome material were sliced into sections (1-cm thick, from the surface), and horizon 2 (1 to 2 cm) was chosen for the microbial community analysis.DNA extraction and purification. A combination of the methods described by Zhou et al. (37) and Gray and Herwig (14) was used. Eight hundred milligrams of ...

No abstract