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A large number of Shiga toxin-producing Escherichia coli (STEC) strains have caused major outbreaks and sporadic cases of human illnesses, including mild diarrhea, bloody diarrhea, hemorrhagic colitis, and the life-threatening hemolytic uremic syndrome. These illnesses have been traced to both O157 and non-O157 STEC. In a large number of STEC-associated outbreaks, the infections were attributed to consumption of ground beef or other beef products contaminated with cattle feces. Thus, beef cattle are considered reservoirs of STEC and can pose significant health risks to humans. The global nature of the human food supply suggests that safety concerns with beef will continue and the challenges facing the beef industry will increase at the production and processing levels. To be prepared to address these concerns and challenges, it is critical to assess the role of beef cattle in human STEC infections. In this review, published reports on STEC in beef cattle were evaluated to achieve the following specific objectives: (i) assess the prevalence of STEC in beef cattle, and (ii) determine the potential health risks of STEC strains from beef cattle. The latter objective is critically important because many beef STEC isolates are highly virulent. Global testing of beef cattle feces revealed wide ranges of prevalence rates for O157 STEC (i.e., 0.2 to 27.8%) and non-O157 STEC (i.e., 2.1 to 70.1%). Of the 261 STEC serotypes found in beef cattle, 44 cause hemolytic uremic syndrome and 37 cause other illnesses.

Mercury (Hg), especially in organic form, is a highly toxic pollutant affecting plants, animals, and man. In plants, the primary target of Hg damage is the chloroplast; Hg inhibits electron transport and photosynthesis. In the present study, chloroplast genetic engineering is used for the first time to our knowledge to enhance the capacity of plants for phytoremediation. This was achieved by integrating a native operon containing the merA and merB genes (without any codon modification), which code for mercuric ion reductase (merA) and organomercurial lyase (merB), respectively, into the chloroplast genome in a single transformation event. Stable integration of the merAB operon into the chloroplast genome resulted in high levels of tolerance to the organomercurial compound, phenylmercuric acetate (PMA) when grown in soil containing up to 400 m PMA; plant dry weights of the chloroplast transformed lines were significantly higher than those of wild type at 100, 200, and 400 m PMA. That the merAB operon was stably integrated into the chloroplast genome was confirmed by polymerase chain reaction and Southern-blot analyses. Northern-blot analyses revealed stable transcripts that were independent of the presence or absence of a 3Ј-untranslated region downstream of the coding sequence. The merAB dicistron was the more abundant transcript, but less abundant monocistrons were also observed, showing that specific processing occurs between transgenes. The use of chloroplast transformation to enhance Hg phytoremediation is particularly beneficial because it prevents the escape of transgenes via pollen to related weeds or crops and there is no need for codon optimization to improve transgene expression. Chloroplast transformation may also have application to other metals that affect chloroplast function.Mercury (Hg) pollution of soil and water is a world-wide problem (Dean et al., 1972; Krämer and Chardonnens, 2001). The extent to which Hg is harmful depends on the form of mercury present in the ecosystem. Inorganic forms of Hg are less harmful than organic forms partly because they bind strongly to the organic components of soil. For this reason, Hg does not tend to contaminate the ground water except when it leaches from a municipal landfill (U.S. Environmental Protection Agency, 1984). Organomercurial compounds, on the other hand, may be 200 times more toxic than inorganic Hg (Patra and Sharma, 2000) and methyl-Hg is especially toxic (Meagher and Rugh, 1997).The principal forms of organomercurial compounds are alkyl mercurials (methyl-and ethyl-Hg), aryl mercurials (phenyl-Hg), and alkoxy alkyl Hg diuretics. The excessive use of organomercurial compounds (e.g. in fertilizers and pesticides) is known to have severe effects on plants. The main site of action of Hg damage appears to be the chloroplast thylakoid membranes and photosynthesis. Organomercurial compounds have been shown to strongly inhibit electron transport, oxygen evolution (Bernier et al., 1993), Hill reaction, photophosphorylation, and to quench chlorophyll ...

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Considering a fractional integro-differential equation with nonlocal conditions involving a general form of Hilfer fractional derivative with respect to another function. We show that weighted Cauchy-type problem is equivalent to a Volterra integral equation, we also prove the existence, uniqueness of solutions and Ulam-Hyers stability of this problem by employing a variety of tools of fractional calculus including Banach fixed point theorem and Krasnoselskii's fixed point theorem. An example is provided to illustrate our main results.

Transgenic tobacco plants engineered with bacterial merA and merB genes via the chloroplast genome were investigated to study the uptake, translocation of different forms of mercury (Hg) from roots to shoots, and their volatilization. Untransformed plants, regardless of the form of Hg supplied, reached a saturation point at 200 microM of phenylmercuric acetate (PMA) or HgCl2, accumulating Hg concentrations up to 500 microg g(-1) with significant reduction in growth. In contrast, chloroplast transgenic lines continued to grow well with Hg concentrations in root tissues up to 2000 microg g(-1). Chloroplasttransgenic lines accumulated both the organic and inorganic Hg forms to levels surpassing the concentrations found in the soil. The organic-Hg form was absorbed and translocated more efficiently than the inorganic-Hg form in transgenic lines, whereas no such difference was observed in untransformed plants. Chloroplast-transgenic lines showed about 100-fold increase in the efficiency of Hg accumulation in shoots compared to untransformed plants. This is the first report of such high levels of Hg accumulation in green leaves or tissues. Transgenic plants attained a maximum rate of elemental-Hg volatilization in two days when supplied with PMA and in three days when supplied with inorganic-Hg, attaining complete volatilization within a week. The combined expression of merAB via the chloroplast genome enhanced conversion of Hg2+ into Hg,0 conferred tolerance by rapid volatilization and increased uptake of different forms of mercury, surpassing the concentrations found in the soil. These investigations provide novel insights for improvement of plant tolerance and detoxification of mercury.

Shiga toxin-producing Escherichia coli (STEC) strains have caused a large number of human illness outbreaks worldwide. In most cases, the infection was traced to consumption of meats or vegetables contaminated with cattle feces. To combat this public health problem, pre- and post-harvest control strategies are continuously implemented to assure food safety. Thus, rapid, reliable, and sensitive methods for STEC detection must be available to provide confidence not only in the meats or vegetables entering the food chain but also in testing humans with illnesses. As a result, enrichment for STEC has been a critical step in any successful protocol for their detection. The base media commonly used for STEC enrichment include sorbitol MacConkey agar, tryptic soy broth (TSB), E. coli broth, enterohemorrhagic E. coli broth, buffered peptone water (BPW), and brain heart infusion broth. In addition to bile salts, antibiotics (e.g., tellurite, cefixime, novobiocin, vancomycin, cefsulodin, and acriflavin) are used at different concentrations to enrich for STEC. In most published reports, however, the reasons for choosing the selective medium were not provided. Thus, this review was intended to evaluate the base media and antibiotics commonly used for STEC detection. The efficacy of a detection method will certainly depend on the choice of the base medium, selective agents, and their concentrations. The interactions among these factors are also expected to affect sensitivity of the detection method, especially when the test sample contains a small number of STEC cells. Because sensitivity of detection is expected to decline when testing for stressed or injured STEC cells, as is the case in environmental samples, a pre-enrichment step in TSB or BPW without antibiotics may be necessary. Future research should focus on identifying possible antibiotic combinations that effectively inhibit most background bacteria without affecting pathogenic STEC strains in the test sample.

The Nevada Plots exclosure system was constructed in 1937 following passage of the Taylor Grazing Act to assess long-term effects of livestock grazing on Nevada rangelands. A comparison of vegetation characteristics inside and outside exclosures was conducted during 2001 and 2002 at 16 sites. Data analysis was performed with a paired t test. Out of 238 cover and density comparisons between inside and outside exclosures at each site, 34 (14% of total) were different (P < 0.05). Generally, where differences occurred, basal and canopy cover were greater inside exclosures and density was greater outside. Shrubs were taller inside exclosures at 3 sites grazed by sheep (Ovis aries). Perennial grasses showed no vertical height difference. Aboveground plant biomass production was different at only 1 site. Plant community diversity inside and outside exclosures were equal at 11 of 16 sites. Species richness was similar at all sites and never varied > 4 species at any site. Few changes in species composition, cover, density, and production inside and outside exclosures have occurred in 65 years, indicating that recovery rates since pre Taylor Grazing Act conditions were similar under moderate grazing and grazing exclusion on these exclosure sites. Resumen El sistema de exclusiones de Nevada se construyó en 1937, después de ser aprobada el Acta Taylor de Apacentamiento, para evaluar los efectos a largo plazo del apacentamiento del ganado sobre los pastizales de Nevada. Durante los años 2001 y 2002, en 16 sitios se condujo una comparación de las características de la vegetación dentro y fuera de las exclusiones. El análisis de los datos se llevo a cabo mediante pruebas de t-student para muestras apareadas. De 238 comparaciones de cobertura y densidad de la vegetación dentro y fuera de las exclusiones, 34 de ellas (14% del total) fueron diferentes (P < 0.05). Generalmente, donde ocurrieron las diferencias, la cobertura basal y de la copa fueron mayores dentro de las exclusiones y la densidad fue mayor fuera de ellas. En tres sitios apacentados con ovinos (Ovis aries) los arbustos fueron mas altos dentro de las exclusiones. Los zacates perennes no mostraron diferencias verticales de altura. La producción de biomasa vegetal aérea fue diferente solo en un sitio. La diversidad de la comunidad vegetal dentro y fuera de las exclusiones fue igual en 11 de los 16 sitios. La riqueza de especies fue similar en todos los sitios y nunca varió por más de 4 especies en ninguno de ellos. Pocos cambios han ocurrido en 65 años en la composición de especies, cobertura, densidad y producción dentro y fuera de las exclusiones, indicando que en estos sitos de exclusión las tasas de recuperación anteriores a las condiciones establecidas por el Acta Taylor fueron similares bajo un apacentamiento moderado y la exclusión al apacentamiento.