Resistance of upland-rice lines to root-knot nematode, Meloidogyne incognita.

Despite the benefits of crop rotation, occurrence of nematodes is a common problem for almost all crops within the Cerrado biome, especially for rice. The use of resistant cultivars is one of the main methods for control of nematodes. Thus, the present study aimed to evaluate the reaction of 36 upland-rice lines, with desirable agronomic characteristics, according to their resistance to root-knot nematodes (Meloidogyne incognita). The experimental design was entirely randomized with four replications. Each plot of land consisted of two rice plants in a 3-L vase. The plants were inoculated with 1000 eggs and eventual juveniles of the respective nematodes. Fifty-five days after the inoculation, the roots and the aerial part of the plant were weighed and the egg mass (EM) as well as the reproduction factor (Rf) were estimated. It was determined that the isolated use of EM was not beneficial in selecting rice lines resistant to the root-knot nematode. This procedure must, therefore, take into account the egg counting and the Rf, in order to improve the reliability of the selection. In our study, 30 evaluated lines were observed to be resistant. Among the recommended cultivars, only BRS Monarca had its performance susceptible to the studied nematode species.

Monitoring subtropical aquatic ecosystems: evaluating the use of Trophic State Indices (TSI) and Aquatic Life Protection (API) as baseline indices by monitoring an urban reservoir in southeastern Brazil.

The use of indices is recommended for continuous monitoring and assessment of aquatic ecosystems, as they summarize the technical complexity of the results of multiple analyzes performed and translate these results into quality classes that reflect the actions taken and indicate ways to recover and conserve the resources. Environmental trophic state indices provide information on how nutrients, light availability and other factors promote the development of algal biomass and contribute to increased enrichment status of aquatic systems. Lamparelli's Trophic State Index (TSI) distinguishes between lentic (lower phytoplankton productivity) and lotic (higher phosphorus concentrations and lower chlorophyll-a concentrations) environments. The Aquatic Life Protection Index (ALPI) reflects water quality based on the trophic state of the environment, determines the degree of toxicity to biota and indicates deficiencies in variables and conditions essential for the protection of aquatic life. The indices were applied to a long data series to monitor the Guarapiranga Reservoir, an urban reservoir in the state of São Paulo in southeastern Brazil, which suffers from the urbanization of its surroundings and the discharge of domestic wastewater. The evaluation of the time series from 1978 to 2021 using these indices showed a deterioration in the trophic status and conservation of aquatic life in the reservoir and in one of its tributaries. Considering that the joint assessment of the two indices provides an approach to environmental conservation, their long-term use reflected changes and impacts on the environment and showed the best-preserved sites. Both indices are suitable for application in a baseline network in subtropical environments. They can pinpoint locations for better monitoring and are sensitive to environmental changes.

Anthropogenic debris ingestion in a tropical seabird community: Insights from taxonomy and foraging distribution.

Oceans have been considered as an unlimited supply of goods and services, but resource extraction and waste disposal became ubiquitous and have been damaging the health of marine ecosystems. Finding suitable sentinel species of the human impacts on the oceans is thus imperative, since they may work as early warnings of disruptive situations. In this study, we investigated how taxonomy and foraging distribution influenced the occurrence of anthropogenic debris among five seabird species inhabiting the tropical Atlantic region. Occurrence of anthropogenic debris was assessed using faeces of breeding individuals as a proxy of ingestion. A total of 268 particles were extracted from all samples. The categories "fragments" and "fibres", as well as the colour "blue", were the most prevalent characteristics across species. There was a high diversity of polymers from cellulosic particles to synthetic plastics (Anthropogenic Cellulosic 26.9 %; Polyester 7.7 %; Varnish 5.8 %; Polypropylene 1.9 %). Species with a more coastal foraging strategy exhibited higher occurrence and number of anthropogenic debris when compared to species foraging comparably more in pelagic areas. This suggests that anthropogenic debris are more prevalent in coastal foraging areas, where human activities occur in higher number and frequency (e.g., fisheries) and sources of freshwater input from inland are at close distance. These results provide more evidence to the growing perception on the ubiquity and diversity of anthropogenic debris in the marine environment, and further support the usefulness of using seabirds as bio-indicators of anthropogenic pollution in both neritic and oceanic regions.

Is leaf fluctuating asymmetry related to plant and leaf size in Miconia albicans, a common Melastomataceae species?

Fluctuating asymmetry, defined as random differences between the two sides of a symmetrical structure, has been often related to development stress in both plants and animals. In plants, leaf fluctuating asymmetry has been related to stresses such as pollution and fire and may also be related to leaf growth and herbivory rates. We assessed whether leaf fluctuating asymmetry is related to plant and leaf size in Miconia albicans (Sw.) Triana (Melastomataceae), a common multi-stem Neotropical shrub, in a Brazilian savanna area. We collected 15 leaves from each of 70 individuals, and measured fluctuating asymmetry as the difference in area between the right and left sides of the leaves using the central vein as reference. To avoid spurious results due to measurement error, the division along the central vein was performed independently by three researchers. We also measured the basal area and height of each stem of the plant individuals. We used linear models to assess the relations between leaf fluctuating asymmetry, plant size and leaf size. No consistent relations were observed between leaf fluctuating asymmetry and plant size, as the analyses performed on the fluctuating asymmetry values obtained by the different researchers showed different results. However, relative fluctuating asymmetry values, obtained by dividing the fluctuating asymmetry by the total leaf area, tended to be smaller in larger leaves. It thus appears that, in the study species, fluctuating asymmetry is related to the developmental conditions faced by the individual leaves and not by the plant as a whole.

Efficient choice of colored noise in the stochastic dynamics of open quantum systems.

The stochastic Liouville-von Neumann (SLN) equation describes the dynamics of an open quantum system reduced density matrix coupled to a non-Markovian harmonic environment. The interaction with the environment is represented by complex colored noises which drive the system, and whose correlation functions are set by the properties of the environment. We present a number of schemes capable of generating colored noises of this kind that are built on a noise amplitude reduction procedure [Imai et al., Chem. Phys. 446, 134 (2015)CMPHC20301-010410.1016/j.chemphys.2014.11.014], including two analytically optimized schemes. In doing so, we pay close attention to the properties of the correlation functions in Fourier space, which we derive in full. For some schemes the method of Wiener filtering for deconvolutions leads to the realization that weakening causality in one of the noise correlation functions improves numerical convergence considerably, allowing us to introduce a well-controlled method for doing so. We compare the ability of these schemes, along with an alternative optimized scheme [Schmitz and Stockburger, Eur. Phys. J.: Spec. Top. 227, 1929 (2019)1951-635510.1140/epjst/e2018-800094-y], to reduce the growth in the mean and variance of the trace of the reduced density matrix, and their ability to extend the region in which the dynamics is stable and well converged for a range of temperatures. By numerically optimizing an additional noise scaling freedom, we identify the scheme which performs best for the parameters used, improving convergence by orders of magnitude and increasing the time accessible by simulation.

Dual role for the tyrosine decarboxylation pathway in Enterococcus faecium E17: response to an acid challenge and generation of a proton motive force.

In this work we investigated the role of the tyrosine decarboxylation pathway in the response of Enterococcus faecium E17 cells to an acid challenge. It was found that 91% of the cells were able to remain viable in the presence of tyrosine when they were incubated for 3 h in a complex medium at pH 2.5. This effect was shown to be related to the tyrosine decarboxylation pathway. Therefore, the role of tyrosine decarboxylation in pH homeostasis was studied. The membrane potential and pH gradient, the parameters that compose the proton motive force (PMF), were measured at different pHs (pH 4.5 to 7). We obtained evidence showing that the tyrosine decarboxylation pathway generates a PMF composed of a pH gradient formed due to proton consumption in the decarboxylation reaction and by a membrane potential which results from electrogenic transport of tyrosine in exchange for the corresponding biogenic amine tyramine. The properties of the tyrosine transporter were also studied in this work by using whole cells and right-side-out vesicles. The results showed that the transporter catalyzes homologous tyrosine/tyrosine antiport, as well as electrogenic heterologous tyrosine-tyramine exchange. The tyrosine transporter had properties of a typical precursor-product exchanger operating in a proton motive decarboxylation pathway. Therefore, the tyrosine decarboxylation pathway contributes to an acid response mechanism in E. faecium E17. This decarboxylation pathway gives the strain a competitive advantage in nutrient-depleted conditions, as well as in harsh acidic environments, and a better chance of survival, which contributes to higher cell counts in food fermentation products.

Contrasting human cytokine responses to promastigote whole-cell extract and the Leishmania analogue receptor for activated C kinase antigen of L. amazonensis in natural infection versus immunization.

It is known that the same antigen can induce different immune responses, depending upon the way that it is presented to the immune system. The objective of this study was to compare cytokine responses of peripheral blood mononuclear cells (PBMC) from cutaneous leishmaniasis patients and subjects immunized with a first-generation candidate vaccine composed of killed Leishmania amazonensis promastigotes to a whole-cell promastigote antigen extract (La) and to the recombinant protein LACK (Leishmania analogue receptor for activated C kinase), both from L. amazonensis. Thirty-two patients, 35 vaccinees and 13 healthy subjects without exposure to Leishmania, were studied. Cytokine production was assessed by enzyme-linked immunosorbent assay and enzyme-linked immunospot assay. The interferon (IFN)-gamma levels stimulated by La were significantly higher and the levels of interleukin (IL)-10 significantly lower than those stimulated by LACK in the patient group, while LACK induced a significantly higher IFN-gamma production and a significantly lower IL-10 production compared with those induced by La in the vaccinated group. LACK also induced a significantly higher frequency of IFN-gamma-producing cells than did La in the vaccinated group. The contrast in the cytokine responses stimulated by LACK and La in PBMC cultures from vaccinated subjects versus patients indicates that the human immune response to crude and defined Leishmania antigens as a consequence of immunization differs from that induced by natural infection.

Detection of Th1/Th2 cytokine signatures in yellow fever 17DD first-time vaccinees through ELISpot assay.

Immunity to yellow fever (YF) is conferred by the interplay of humoral and cellular immune response. Despite the extensive literature on the humoral immune response to the YF vaccine virus, little is known about its cellular immune response to vaccination. The analysis of cytokine production by ex-vivo antigen-stimulated T cells has been considered as a valuable tool for understanding cellular immune response. Thus, we have analyzed two T(H)1/T(H)2 signature cytokines (IFN-gamma and IL-4) from 12 healthy first-time adults vaccinated with YF17DD virus. The cells, harvested on day 0 (before vaccination) and 7, 15 and 30 days after immunization were antigen-stimulated and analyzed by ELISpot. A significant increase in the number of spot-forming cells during the response to YF 17DD live virus stimulation by ELISpot assay was observed. IFN-gamma-and IL-4-producing cells were significantly increased on the 15th day after vaccination in all volunteers. These results presented herein are important for understanding the role of cytokines in the immune response to YF 17DD virus.

Immunosuppressive monocytes (CD14+/HLA-DRlow/-) increase in childhood precursor B-cell acute lymphoblastic leukemia after induction chemotherapy.

In tumor microenvironment, immunosuppression is a common event and results from the inhibition of activated immune cells and generation of cells with immunosuppressive capacity, as some subtypes of monocytes. The aim of this study was to evaluate the presence of immunosuppressive CD14+/HLA-DRlow/- monocytes in pediatric patients with the diagnosis of B-cell acute lymphoblastic leukemia (B-ALL) and, moreover, verify whether the chemotherapeutic treatment has any effect on these cells. Peripheral blood (PB) and bone marrow (BM) samples were collected from 15 untreated pediatric patients. The presence of CD14+/HLA-DRlow/- monocytes was evaluated at diagnosis and in the end of induction chemotherapy by flow cytometry. CD14+/HLA-DRlow/- monocytes increase was observed in 60% (9/15) of the patients at the end of the induction therapy. We were able to detect an increase in CD14+/HLA-DRlow/- monocytes values in BM and PB samples of pediatric patients with B-ALL. This increase was observed in the end of induction chemotherapy, which leads us to believe that these changes probably could have been induced by the inflammatory process engendered by the cytotoxic treatment or by drugs used in the chemotherapy treatment. This finding may be useful to guide new therapeutic approaches contemplating immunomodulatory drugs that act in the depletion of immunosuppressive monocytes.

Effects of an accidental dry-season fire on the reproductive phenology of two Neotropical savanna shrubs.

Fire is a recurrent disturbance in savanna vegetation and savanna species are adapted to it. Even so, fire may affect various aspects of plant ecology, including phenology. We studied the effects of a spatially heterogeneous fire on the reproductive phenology of two dominant woody plant species, Miconia albicans (Melastomataceae) and Schefflera vinosa (Araliaceae), in a savanna area in South-eastern Brazil. The study site was partially burnt by a dry-season accidental fire in August 2006, and we monitored the phenolology of 30 burnt and 30 unburnt individuals of each species between September 2007 and September 2008. We used restricted randomizations to assess phenological differences between the burnt and unburnt individuals. Fire had negative effects on the phenology of M. albicans, with a smaller production of reproductive structures in general and of floral buds, total fruits, and ripe fruits in burnt plants. All unburnt but only 16% of the burnt M. albicans plants produced ripe fruits during the study. Fire effects on S. vinosa were smaller, but there was a greater production of floral buds and fruits (but not ripe fruits) by burnt plants; approximately 90% of the individuals of S. vinosa produced ripe fruits during the study, regardless of having been burnt or not. The differences between the two species may be related to S. vinosa's faster growth and absence from the seed bank at the study site, whereas M. albicans grows more slowly and is dominant in the seed bank.

Ileostomy or colostomy for temporary decompression of colorectal anastomosis.

BACKGROUND: The use of loop ileostomy or loop transverse colostomy represents an important issue in colorectal surgery. Despite a slight preference for a loop ileostomy as a temporary stoma, the best form for temporary decompression of colorectal anastomosis still remains controversial. OBJECTIVES: To assess the evidence in the use of loop ileostomy compared with loop transverse colostomy for temporary decompression of colorectal anastomosis, comparing the safety and effectiveness. SEARCH STRATEGY: We identified randomised controlled trials from MEDLINE, EMBASE, Lilacs, and the Cochrane Central Register of Controlled Trials. Further, by hand-searching relevant medical journals and proceedings from major gastroenterological congresses. We did not limit the seaches regarding date and language. SELECTION CRITERIA: We assessed all randomised clinical trials, that met the objectives and reported major outcomes: 1. Mortality; 2. Wound infection; 3. Time of formation of stoma; 4. Time of closure of stoma; 5. Time interval between formation and closure of stoma; 6. Stoma prolapse; 7. Stoma retraction; 8. Parastomal hernia; 9. Parastomal fistula; 10. Stenosis; 11. Necrosis; 12. Skin irritation; 13. Ileus; 14. Bowel leakage; 15. Reoperation; 16. Patient adaptation; 17. Length of hospital stay; 18. Colorectal anastomotic dehiscence; 19. Incisional hernia; 20. Postoperative bowel obstruction. DATA COLLECTION AND ANALYSIS: Details of the randomisation, blinding, whether an intention-to-treat analysis was done, and the number of patients lost to follow-up was recorded. For data analysis the relative risk and risk difference were used with corresponding 95% confidence interval; fixed effect was used for all outcomes unless incisional hernia (random effect model). Statistical heterogeneity in the results of the meta-analysis was assessed by inspection of graphical presentation (funnel plot) and by calculating a test of heterogeneity. MAIN RESULTS: Five trials were included with 334 patients: 168 to loop ileostomy group and 166 to loop transverse colostomy group. The continuous outcomes could not be measured because of the lack of the data. The outcomes stoma prolapse had statistical significant difference: p=0.00001, but with statistical heterogeneity, p=0,001. When the sensitive analysis was applied excluding the trials that included emergencies surgeries, the result had a discreet difference: p = 0.02 and Test for heterogeneity: chi-square = 0.78, df = 2, p = 0.68, I(2)=0%. AUTHORS' CONCLUSIONS: The best available evidence for decompression of colorectal anastomosis, either use of loop ileostomy or loop colostomy, could not be clarified from this review. So far, the results in terms of occurrence of postoperative stoma prolapse support the choice of loop ileostomy as a technique for fecal diversion for colorectal anastomosis, but large scale RCT's is needed to verify this.

Intragastric balloon for obesity.

BACKGROUND: Obesity is one of the major public health problems of modern society. Intragastric balloon (IGB) treatment for obesity has been developed as a temporary aid. Its primary objective is the treatment of obese people, who have had unsatisfactory results in their clinical treatment for obesity, despite of being cared for by a multidisciplinary team, and super obese patients with a higher surgical risk. However, the effects of different IGB procedures compared with conventional treatments and with each other are uncertain. OBJECTIVES: To assess the effects of intragastric balloon in people with obesity. SEARCH STRATEGY: Studies were obtained from computerised searches of MEDLINE, EMBASE, LILACS, The Cochrane Library and other electronic databases. Furthermore, reference lists of relevant articles and hand searches of selected journals were performed. Experts in the field were contacted. SELECTION CRITERIA: Randomised and quasi-randomised controlled trials fulfilling the inclusion criteria were used. Short term weight loss is common, so studies were included if they reported measurements after a minimum of four weeks follow-up. DATA COLLECTION AND ANALYSIS: Data were extracted by one reviewer and checked independently by two reviewers. Two reviewers independently assessed the quality of trials. MAIN RESULTS: Nine randomised controlled trials involving 395 patients were included. Six out of nine studies had a follow-up of less than one year, the longest study duration was 24 months. Only a third of the analysed studies revealed a low risk of bias. No information was available on quality of life, all-cause mortality and morbidity. Compared with conventional management, IGB did not show convincing evidence of a greater weight loss. On the other hand, complications of intragastric balloon placement occurred, however few of a serious nature. The relative risks for minor complications like gastric ulcers and erosions were significantly raised. AUTHORS' CONCLUSIONS: Evidence from this review is limited for decision making, since there was large heterogeneity in IGB trials, regarding both methodological and clinical aspects. However, a co-adjuvant factor described by some authors in the loss and maintenance of weight has been the motivation and the encouragement to changing eating habits following a well-organized diet and a program of behavioural modification. The IGB alone and the technique of positioning appear to be safe. Despite the evidence for little additional benefit of the intragastric balloon in the loss of weight, its cost should be considered against a program of eating and behavioural modification.

Telomere length analysis in monoclonal B-cell lymphocytosis and chronic lymphocytic leukemia Binet A.

Monoclonal B-cell lymphocytosis (MBL) is an asymptomatic clinical entity characterized by the proliferation of monoclonal B cells not meeting the diagnosis criteria for chronic lymphocytic leukemia (CLL). MBL may precede the development of CLL, but the molecular mechanisms responsible for disease progression and evolution are not completely known. Telomeres are usually short in CLL and their attrition may contribute to disease evolution. Here, we determined the telomere lengths of CD5+CD19+ cells in MBL, CLL, and healthy volunteers. Twenty-one CLL patients, 11 subjects with high-count MBL, and 6 with low-count MBL were enrolled. Two hundred and sixty-one healthy volunteers aged 0 to 88 years were studied as controls. After diagnosis confirmation, a flow cytometry CD19+CD5+-based cell sorting was performed for the study groups. Telomere length was determined by qPCR. Telomere length was similar in the 3 study groups but shorter in these groups compared to normal age-matched subjects that had been enrolled in a previous study from our group. These findings suggest that telomere shortening is an early event in CLL leukemogenesis.

Adhesion molecule profiles of B-cell non-Hodgkin's lymphomas in the leukemic phase.

We evaluated the expression of 10 adhesion molecules on peripheral blood tumor cells of 17 patients with chronic lymphocytic leukemia, 17 with mantle-cell lymphoma, and 13 with nodal or splenic marginal B-cell lymphoma, all in the leukemic phase and before the beginning of any therapy. The diagnosis of B-cell non-Hodgkin's lymphomas was based on cytological, histological, immunophenotypic, and molecular biology methods. The mean fluorescence intensity of the adhesion molecules in tumor cells was measured by flow cytometry of CD19-positive cells and differed amongst the types of lymphomas. Comparison of chronic lymphocytic leukemia and mantle-cell lymphoma showed that the former presented a higher expression of CD11c and CD49c, and a lower expression of CD11b and CD49d adhesion molecules. Comparison of chronic lymphocytic leukemia and marginal B-cell lymphoma showed that the former presented a higher expression of CD49c and a lower expression of CD11a, CD11b, CD18, CD49d, CD29, and CD54. Finally, comparison of mantle-cell lymphoma and marginal B-cell lymphoma showed that marginal B-cell lymphoma had a higher expression of CD11a, CD11c, CD18, CD29, and CD54. Thus, the CD49c/CD49d pair consistently demonstrated a distinct pattern of expression in chronic lymphocytic leukemia compared with mantle-cell lymphoma and marginal B-cell lymphoma, which could be helpful for the differential diagnosis. Moreover, the distinct profiles of adhesion molecules in these diseases may be responsible for their different capacities to invade the blood stream.

Evaluation of sequential perfusion with Euro-Collins and Belzer solutions for pancreas preservation in rats.

OBJECTIVE: To investigate the effect of Euro-Collins and Belzer solutions in a sequential preservation of the pancreas. METHODS: Forty-five Wistar-EPM rats were divided into four groups, according to the solution used during preservation: (1) saline solution (SF): animals perfused and preserved with saline solution; (2) Euro-Collins group (C): animals perfused and preserved with Euro-Collins solution; (3) Belzer group (B): animals perfused and preserved with Belzer solution; (4) Euro-Collins/Belzer group (CB): animals perfused with equal parts of Euro-Collins and Belzer solutions sequentially and preserved with Belzer solution. After perfusion, the animals underwent pancreas resection and preservation with the respective substance at 4 degrees C. Amylase was measured in the preservation solution after 12, 24, 36, or 48 hours. Finally, the pancreas was analyzed histologically, and a statistical analysis was performed. RESULTS: Groups SF and C showed the highest amylase levels in the preservation solution during all periods. The levels were higher than in groups C and CB (P = .05). Amylase levels were similar in groups B and CB to 24 hours (P = .05). Histological analysis was significant for analysis of pancreas islet cells and edema. Groups B and CB were histologically similar (P = .001) and different from groups SF and C. CONCLUSION: Sequential perfusion using Euro-Collins and Belzer solutions was effective for pancreas preservation in rats up to 24 hours.

The risks of introduction of the Amazonian palm Euterpe oleracea in the Atlantic rainforest.

The introduction of a species may alter ecological processes of native populations, such as pollination and dispersal patterns, leading to changes in population structure. When the introduced and the native species are congeners, interference in pollination can also lead to hybridization. We aimed to understand the ecological aspects of Euterpe oleracea introduction in the Atlantic forest and the possible consequences for the conservation of the native congener Euterpe edulis. We analysed the population structure of palm populations, including hybrids, and observed the interaction with frugivorous birds of both palm species after E. oleracea introduction. We observed that E. edulis had significantly lower density and a smaller number of seedlings when occurring with E. oleracea. Native and introduced Euterpe species shared nine frugivorous bird species. E. oleracea and hybrids had dispersed outside the original planting area. Consequently, the risks of introduction of E. oleracea may mostly be related to the disruption of interactions between E. edulis and frugivorous birds and the spontaneous production of hybrids. Finally, the cultivation of E. oleracea and hybrids in Atlantic rainforest could affect the conservation of the already endangered E. edulis.

The role of Pteridium arachnoideum(Kaulf) on the seed bank of the endangered Brazilian Cerrado.

The native bracken (Pteridium arachnoideum) often occurs in mono-specific stands in the Brazilian Cerrado, and this dominance can impact on both the above-ground vegetation and soil seed bank. This study investigated how invasion by this species over a 20-year period changed the seed bank and the relationship between the seed bank and litter mass. We extracted soil samples from three replicated invaded and uninvaded sites, and followed seedling emergence for six months. We collected the above-ground biomass and litter of P. arachnoideum in ten 1m2 plots from three invaded sites. There was no difference between invaded and uninvaded areas in seed bank richness, diversity or overall abundance. The most abundant family was the Melastomataceae, followed by the Poaceae. The Melastomataceae was more abundant in uninvaded sites, but the most common species of this family (Tibouchinastenocarpa) was not affected. The grasses were more common in invaded sites in the rainy season and were affected by heterogeneity in the litter layer. The seed bank could play a role in the recovery of these invaded areas, but the presence of weeds and invasive grasses could constrain their use as a management strategy.

Mechanical bowel preparation for elective colorectal surgery.

BACKGROUND: For over a century the presence of bowel content during surgery has been linked to anastomotic leakage. Mechanical bowel preparation has been considered an efficient agent against leakage and infectious complications. This dogma is not based on solid evidence, but on observational data and expert's opinions. OBJECTIVES: To determine the effectiveness and safety of prophylactic mechanical bowel preparation for morbidity and mortality rates in elective colorectal surgery. SEARCH STRATEGY: We searched MEDLINE, EMBASE, LILACS, and the Cochrane Central Register of Controlled Trials. We also searched relevant medical journals, and conference proceedings from major gastroenterological congresses and contacted experts in the field. We used the search strategy described by the Colorectal Cancer Review Group, without limitations for date of publication and language. I SELECTION CRITERIA: Randomised, clinical trials that compared any strategy in mechanical bowel preparation with no mechanical bowel preparation. DATA COLLECTION AND ANALYSIS: Data were independently extracted by the reviewers and cross-checked. The same reviewers assessed the methodological quality of each trial. Details of the randomisation (generation and concealment), blinding, whether an intention-to-treat analysis was done, and the number of patients lost to follow-up was recorded. For analysis the Peto odds ratio (OR) was used as defaults. MAIN RESULTS: Of the 1592 patients (9 trials), 789 were allocated to mechanical bowel preparation (Group A) and 803 to no preparation (Group B) before elective colorectal surgery. For anastomotic leakage (main outcome) the results were: - Low anterior resection: 9.8% (11 of 112 patients in Group A) compared with 7.5% (9 of 119 patients in Group B); Peto OR 1.45, 95% confidence interval (CI): 0.57 to 3.67 (non-significant); - Colonic surgery: 2.9% (Group A) compared with 1.6% (Group B) ; Peto OR 1.80, 95% CI: 0.68 to 4.75 (non-significant); Overall anastomotic leakage: 6.2% (Group A) compared with 3.2% (Group B); Peto OR 2.03, 95% CI: 1.276 to 3.26 (p=0.003). For the secondary outcome of wound infection the result was: 7.4% (Group A) compared with 5.4% (Group B); Peto OR 1.46, 95% CI: 0.97 - to 2.18 (p=0.07); Sensitivity analyses excluding studies with dubious randomisation, studies published as abstracts only, and studies involving children did not change the overall conclusions AUTHORS' CONCLUSIONS: There is no convincing evidence that mechanical bowel preparation is associated with reduced rates of anastomotic leakage after elective colorectal surgery. On the contrary, there is evidence that this intervention may be associated with an increased rate of anastomotic leakage and wound complications. It is not possible to be conclusion on the latter issue because of the clinical heterogeneity of trial inclusion criteria, methodological inadequacies in trial (in particular, poor reporting of concealment and allocation), potential performance biases, and failure of intention-to-treat analyses. Nevertheless, the dogma that mechanical bowel preparation is necessary before elective colorectal surgery should be reconsidered.