The prevalence of ampicillin-resistant opportunistic pathogenic bacteria undergoing selective stress of heavy metal pollutants in the Xiangjiang River, China.

The emergence of clinically relevant ß-lactam-resistant bacteria poses a serious threat to human health and presents a major challenge for medical treatment. How opportunistic pathogenic bacteria acquire antibiotic resistance and the prevalence of antibiotic-resistant opportunistic pathogenic bacteria in the environment are still unclear. In this study, we further confirmed that the selective pressure of heavy metals contributes to the increase in ampicillin-resistant opportunistic pathogens in the Xiangjiang River. Four ampicillin-resistant opportunistic pathogenic bacteria (Pseudomonas monteilii, Aeromonas hydrophila, Acinetobacter baumannii, and Staphylococcus epidermidis) were isolated on Luria-Bertani (LB) agar plates and identified by 16S rRNA sequencing. The abundance of these opportunistic pathogenic bacteria significantly increased in the sites downstream of the Xiangjiang River that were heavily influenced by metal mining activities. A microcosm experiment showed that the abundance of ß-lactam resistance genes carried by opportunistic pathogenic bacteria in the heavy metal (Cu2+ and Zn2+) treatment group was 2-10 times higher than that in the control. Moreover, heavy metals (Cu2+ and Zn2+) significantly increased the horizontal transfer of plasmids in pathogenic bacteria. Of particular interest is that heavy metals facilitated the horizontal transfer of conjugative plasmids, which may lead to the prevalence of multidrug-resistant pathogenic bacteria in the Xiangjiang River.

Occurrence and distribution of clinical and veterinary antibiotics in the faeces of a Chinese population.

Antibiotics ingested in the human gut may create selective pressure to change the composition of the gut microbiota, which could adversely effect the immune system of the host. However, the occurrence and distribution of antibiotics in the human gut remains unclear. A total population of 180 individuals, across three Chinses regions with different economic development levels, including children, adults, and elders, were sampled in 2017. A total of 19 representative antibiotics, including both clinical and veterinary antibiotics, were investigated in human faeces. While clinical use and prescriptions were the main exposure pathways for children, environmental media were the exposure pathway to adults. In addition, significant differences (P < 0.05) in antibiotic residues in human faeces were observed amongst various economic development levels, where human faeces from underdeveloped areas were mostly associated with higher levels of antibiotics. This study first to investigate the occurrence and distribution of typical antibiotics in the faeces of a Chinese population and thereby provide a reference for the intensive study of the effects and mechanisms of antibiotics on human gut microbiota.

[Horizontal transfer of antibiotic resistance genes in the environment].

The transfer of antibiotic resistance genes (ARGs), a new type of environmental pollutants, could have more adverse effects on the environment than the ARGs themselves, while the horizontal gene transfer (HGT) could be the most important propagation pathways of the ARGs, being one of the reasons for the growing pollution of ARGs in the environment. This paper systematically elaborated the molecular elements of the horizontal transfer of ARGs and the related affecting factors, which was of significance for investigating the molecular mechanisms of the horizontal transfer of the ARGs. In combining with the phylogenetic mechanisms of multiple antibiotic resistances, this paper also provided effective strategies to reduce the transfer and proliferation of ARGs in the environment. Based on the present contamination situations, the further researches on the horizontal transfer of ARGs in the environment were prospected.

[Analysis of conserved flanking elements associated with antibiotic resistance genes dissemination].

The overuse of antibiotics in medicine, animal husbandry, and aquiculture industry increases the emergence of antibiotic resistant bacteria and antibiotic resistance genes (ARGs), and also, accelerates the dissemination of ARGs within environmental bacteria. In this study, the total DNA was directly extracted from environmental samples, and the upstream and downstream of antibiotic resistance genes were directly amplified by thermal asymmetric interlaced PCR (Tail-PCR) technique. By optimizing the Tail-PCR program, the multiple flanking sequences of tetW, including 6 upstream sequences and 9 downstream sequences, were simultaneously acquired. Through the bioinformatics analysis, the upstream of tetW presented a perfect inverted repeat (IR), a known tetW regulator peptide, and an insertional sequence (IS), whereas the downstream of tetW presented a most conservative fragment and a common open reading frame (ORF) coding methyltransferase. This study not only revealed several conserved flanking tetW gene modules, but also supplied a highly-efficient and convenient methodology for the research of tetW's dissemination within bacteria, i. e., several flanking sequences could be concisely obtained from one sample by using Tail-PCR program.

Electron paramagnetic resonance investigation of in vivo free radical formation and oxidative stress induced by 2,4-dichlorophenol in the freshwater fish Carassius auratus.

In the present study, electron paramagnetic resonance coupled with spin-trapping technique was used, with alpha-phenyl-N-tert-butylnitrone (PBN) as a spin-trapping agent, to investigate free radical generation in freshwater fish with acute 2,4-dichlorophenol (2,4-DCP) poisoning. The PBN-radical adducts were detected in fish liver samples following treatments of 2,4-DCP (0.025, 0.05, 0.5, 5, or 25 mg/kg) 24 h after intraperitoneal (i.p.) injection and 2,4-DCP (0.5 mg/kg) at 2, 4, 8, 24, or 72 h after i.p. injection in Carassius auratus. The hyperfine splitting constants for the PBN-radical adducts are aN = 13.7 G, aH = 1.8 G, and g = 2.0058, which is consistent with those of PBN/hydroxyl radical (*OH). The results indicate that the hydroxyl radical is probably produced during acute intoxication of 2,4-DCP. The relative similarity in the kinetics (from 2 to 72 h) of superoxide dismutase activity induction and *OH generation implies that the generation of *OH possibly depends on the superoxide anion (O2*-). Superoxide anion (O2*-) might be the precursor radical undergoing the Haber-Weiss reaction to form *OH. Possible pathways for radical chain reactions in the formation of the hydroxyl radical in vivo after 2,4-DCP administration are proposed. Other parameters with respect to antioxidant defense (e.g., superoxide dismutase and catalase) and oxidative damage (lipid peroxidation level) indicate that the fish were subjected to oxidative stress induced by 2,4-DCP and that the mechanisms of oxidative stress possibly involve the in vivo stimulation of hydroxyl radical formation.

Decomposition dynamic of higher plant pigments by HPLC analysis.

The fate of the litter of dominant vegetation(willows and reeds) is one of the aspects studied in the frame of the project "Onderzoek Milieu Effecten Sigmaplan". One of the questions to be considered is how long the litter stays within the estuary. In this paper, the time the leaf litter (Salix triandra and Phragmites australis) stayed in the Schelde estuary was studied by using plant pigment as biomarkers with HPLC application. After analyzing the original data from the incubation experiment described by Dubuison and Geers (1999), the decomposition dynamics patterns of pigments were analyzed and described, and these decomposition dynamics patterns were used as calibration patterns. By using Spearman Rank Order Correlation, the calibration patterns of the pigments which were significant (p < 0.05) were grouped. In this way, several groups of the calibration patterns of pigment decomposition were achieved. The presence or absence of these groups of pigments (whether they can be detected or not from HPLC) was shown to be useful in determining the time the litter has stayed in the water. Combining data of DW and POC, more precise timing can be obtained.

Leaf litter ecological fate in the Schelde Estuary in Belgium.

Two dominant species of Willow(Salix triandra) and Reed (Phragmites australis) along the Schelde Estuary(in Belgium) were selected in this research. The pigments of higher plant was used as biomarkers, the decomposition process of the two species were studied after they fall into the Schelde Estuary. After statistical analysis (Spearman rank order correlation, P < 0.05), the results has shown the decomposition dynamics pattern of the pigments, and the willow showed different pattern in comparing with the reed, e.g. Chlorophyll-a decomposition dynamics for willow is: y1 = 12196x2 - 175895x + 1E + 06 + k, R2 = 0.5706 while for reed is: y2 = -37878x2 + 229782x + 734282 + k, R2 = 0.9065. The precise time of the leaf litter spent in the water was also calculated as were less than 24 days, 24-37 days, longer than 37 days(willow) and less than 24 days, longer than 24 days(reed), the leaf litter fate of the two dominant species in the Schelde Estuary was also compared.