Organ-specific accumulation of selenium and mercury in Indo-Pacific bottlenose dolphins (Tursiops aduncus)

A comprehensive study of colisepticaemia progression in layer chickens applying novel tools elucidates pathogenesis and transmission of Escherichia coli into eggs

Colisepticaemia caused by avian pathogenic Escherichia coli (APEC) is a challenging disease due to its high economic importance in poultry, dubious pathogenesis and potential link with zoonosis and food safety. The existing in vitro studies can't define hallmark traits of APEC isolates, suggesting a paradigm shift towards host response to understand pathogenesis. This study investigated the comprehensive pathological and microbial progression of colisepticaemia, and transmission of E. coli into eggs using novel tools. In total 48 hens were allocated into three groups and were inoculated intratracheally with ilux2-E. coli PA14/17480/5-/ovary (bioluminescent strain), E. coli PA14/17480/5-/ovary or phosphate buffered saline. Infection with both strains led to typical clinical signs and lesions of colibacillosis as in field outbreaks. Based on lung histopathology, colisepticaemia progression was divided into four disease stages as: stage I (1-3 days post infection (dpi)), stage II (6 dpi), stage III (9 dpi) and stage IV (16 dpi) that were histologically characterized by predominance of heterophils, mixed cells, pyogranuloma, and convalescence, respectively. As disease progressed, bacterial colonization in host organs also decreased, revealed by the quantification of bacterial bioluminescence, bacteriology, and quantitative immunohistochemistry. Furthermore, immunofluorescence, immunohistochemistry, and bacteria re-isolation showed that E. coli colonized the reproductive tract of infected hens and reached to egg yolk and albumen. In conclusion, the study provides novel insights into the pathogenesis of colisepticemia by characterizing microbial and pathological changes at different disease stages, and of the bacteria transmission to table eggs, which have serious consequences on poultry health and food safety.

Mercury transformations in algae, plants, and animals: The occurrence, mechanisms, and gaps

Mercury (Hg) is a global pollutant showing potent toxicity to living organisms. The transformations of Hg are critical to global Hg cycling and Hg exposure risks, considering Hg mobilities and toxicities vary depending on Hg speciation. Though currently well understood in ambient environments, Hg transformations are inadequately explored in non-microbial organisms. The primary drivers of in vivo Hg transformations are far from clear, and the impacts of these processes on global Hg cycling and Hg associated health risks are not well understood. This hinders a comprehensive understanding of global Hg cycling and the effective mitigation of Hg exposure risks. Here, we focused on Hg transformations in non-microbial organisms, particularly algae, plants, and animals. The process of Hg oxidation/reduction and methylation/demethylation in organisms were reviewed since these processes are the key transformations between the dominant Hg species, i.e., elemental Hg (Hg0), divalent inorganic Hg (IHgII), and methylmercury (MeHg). By summarizing the current knowledge of Hg transformations in organisms, we proposed the potential yet overlooked drivers of these processes, along with potential challenges that hinder a full understanding of in vivo Hg transformations. Knowledge summarized in this review would help achieve a comprehensive understanding of the fate and toxicity of Hg in organisms, providing a basis for predicting Hg cycles and mitigating human exposure.

Selenium and mercury concentrations, Se:Hg molar ratios and their effect on the antioxidant system in wild mammals

The aim of this study was to a) evaluate the concentration of Se and Hg and their relationship in the tissues of 4 species of wild mammals, including Se:Hg molar ratios, and b) evaluate the effect of the analysed elements and their mutual proportions expressed as Se:Hg molar ratio, on the antioxidant system in the tissues of the tested animals. The study was performed on 31 animals belonging to four species: wild boar, red fox, roe deer, brown hare. Determination of Hg in liver, kidney and muscle of animals was performed using an AMA 254 mercury analyser. Total Se concentrations were determined using the spectrofluorometric method. In omnivores demonstrated higher Se concentrations in all analysed organs compared to the herbivores. The highest concentration of Hg was found in the kidneys of the tested animals, and the lowest in the muscles. High and moderate correlation between Se and Hg was observed in the liver of omnivorous, while in herbivores this correlation was weak. In all analysed samples, the Se:Hg molar ratios were above 1 (min: liver 5.9, max: kidney 110). Generally, the highest Se:Hg ratio values were found in kidney and the lowest in liver of tested animals. No significant correlation was found between GPx, GST and SOD activity and Se or Hg concentration in analysed organs. But it was observed that Se:Hg molar was negatively correlated with CAT activity in the most samples. The obtained results may suggest that omnivorous animals demonstrate greater Hg sequestration in the liver than herbivores, which has been proposed as one of the mechanisms of Se antagonistic action towards Hg. The ratio between Se and Hg, rather than the concentration of these elements in organs, affected the antioxidant status in the animal organism, specifically the CAT activity.