Duplex real-time fluorescent recombinase polymerase amplification for the rapid and sensitive detection of two resistance genes in drug-resistant Staphylococcus aureus.

In the clinic, drug-resistant Staphylococcus aureus (S. aureus) is the most common suppurative infection pathogen in humans. It can cause local infections in humans and animals, such as pneumonia, mastitis, and other systemic illnesses. At present, the detection of drug-resistant S. aureus includes traditional isolation by culture and antimicrobial susceptibility tests. However, these methods are complicated in experimental design, specialized in operation and time consuming. Therefore, a rapid and accurate drug-resistant S. aureus detection technology is urgently needed. In this study, we combined duplex pairs of fluorescent probes with recombinase polymerase amplification (RPA) to realize the simultaneous detection of two resistance genes in drug-resistant S. aureus. The method shows low detection limit, detecting 20 copies within 10 min. The analytical specificity of this method was evaluated with several related drug-resistant bacterial strains (Non-resistant S. aureus, Acinetobacter baumannii, Pseudomonas aeruginosa, Escherichia coli and Klebsiella pneumoniae), and the positive signal was only observed with drug-resistant S. aureus. In addition, the clinical suitability of this method was verified by 30 clinical isolates. Compared with qPCR, the coincidence rate of drug resistance genes were 100% (mecA) and 96.7% (ermA), respectively. These results show that the duplex real-time fluorescent RPA assay is a rapid, low detection limit and specific detection of mecA and ermA genes in isolates of drug-resistant S. aureus.

Microscale spatial variability of Beryllium-7 at a reference site in southwest China.

Quantitative assessment of soil erosion and deposition rates using fallout radionuclides (FRNs), including Beryllium-7 (7Be), requires establishment of a reliable reference inventory i.e. the inventory of a non-eroding point. Little information, however, is currently available on the microscale spatial variability of 7Be inventory within reference sites. This is important information to inform sample design and replication, and in addition, to evaluate the uncertainty of derived soil redistribution data. In this study, soil samples were taken systematically at grid points on a 5 m × 12 m experimental reference plot with a bare soil surface, at two sampling occasions (2019 and 2021) in southwest China. 7Be activities were measured to explore the potential variability of 7Be inventory at the microscale. To determine possible causes of 7Be inventory variation, physicochemical characteristics including organic matter content (OM), pH, cation exchange capacity (CEC) and grain size compositions were analyzed at each sample location. 7Be inventories for the two periods were estimated at 211.1 ± 20.0 and 456.1 ± 43.8 Bq m-2 (mean ± 2 SEM, n = 44), with coefficients of variation of 31.4 and 31.9% for the 2019 and 2021 sampling cases, respectively. No significant correlations were observed between 7Be activity and the measured soil compositional properties, suggesting observed spatial variability is primarily a result of random variation due to rainsplash and other processes, although sampling and measuring processes may contribute some uncertainties. Using the traditional method, ca. 40 independent reference samples are required to estimate the mean 7Be inventory, i.e. to represent input across the site, with an allowable error of 10% at 95% confidence, while application of a bootstrap approach suggests that ca. 28 would be adequate under similar accuracy. Overall, results of this study emphasize that the simple assumption of uniform distribution of 7Be across the reference area needs detailed examination on a case-by-case basis, if this radionuclide is to be used effectively to assess patterns and rates of soil redistribution from field to hillslope scale.

Rapid One-Tube RPA-CRISPR/Cas12 Detection Platform for Methicillin-Resistant Staphylococcus aureus.

Methicillin-resistant Staphylococcus aureus (MRSA) is a severe health threat causing high-level morbidity and mortality in health care environments and in community settings. Though existing diagnostic methods, including PCR and culture-based methods, are routinely used in clinical practice, they are not appropriate for rapid point-of-care testing (POCT). Recently, since the development of the CRISPR/Cas technology, new possibilities for rapid point-of-care detection have emerged. In this study, we developed a rapid, accurate, and contamination-free platform for MRSA detection by integrating recombinase polymerase amplification (RPA) with the Cas12 system into one tube. Using this approach, visual MRSA detection could be achieved in 20 min. Based on the one-tube RPA-CRISPR/Cas12a platform, the assay results are visualized by lateral flow test strips (LFS) and fluorescent-based methods, including real-time and end-point fluorescence. This platform allows specific MRSA detection with a sensitivity of 10 copies for the fluorescence method and a range of 10-100 copies for the LFS. The results of 23 samples from clinical MRSA isolates showed that the coincidence rate was 100% and 95.7% of the fluorescence method and LFS, respectively, compared to qPCR. In conclusion, the one-tube RPA-CRISPR/Cas12a platform is an effective method for MRSA detection with significant potential in future practical POCT applications.

137Cs-Based Variation of Soil Erosion in Vertical Zones of a Small Catchment in Southwestern China.

The study of the variability of soil erosion in mountainous areas provides the basis for soil and water conservation work and forest ecological construction in a targeted way. In this study, Liangshan Town catchment, a typical catchment in the Hengduan Mountains region, southwest China, was selected to investigate the variation of soil erosion in different vertical zones using the 137Cs tracing technique. The mean 137Cs reference inventories varied between 573.51 and 705.54 Bq/m2, with the elevation increasing from 1600 to 2600 m. The rates of soil erosion exhibited a significant variation. Under the same land cover condition, the average annual soil erosion modulus of high-elevation forest (elevation > 2200 m) was 400.3 t/(km2·a). However, the average annual soil erosion modulus of a low-elevation sparse forest (elevation < 1600 m) was as high as 1756 t/(km2·a). The average annual soil erosion modulus of the sloping farmland, mainly distributed at elevations of 1600-2200 m, was estimated to be 2771 t/(km2·a). These results indicate that effective soil management measures need to be implemented on the cultivated sloping land in the future.

Estimation of Soil Erosion to Define the Slope Length of Newly Reconstructed Gentle-Slope Lands in Hilly Mountainous Regions.

Farming plot construction engineering in hilly areas plays an important role in the mechanization, large-scale production and industrialization of agriculture. The method is undertaken to improve water and soil conservation, enhance soil fertility and extend machinery agriculture. However, the positive effects of engineering require years to mature. The properties of newly reconstructed soil are not sufficient, i.e., with poor structure and low water holding capacity, resulting in deterioration of its physical properties and erosion. To date, most studies on plot characteristics and soil properties in farming plot construction engineering have neglected the influence of soil erosion. This paper addresses soil erosion characteristics at sites to define the appropriate slope length for newly reconstructed gentle-slope lands. Six field plots with a 10° slope gradient and different lengths (5, 10, 20, 30, 40, and 50 m) were established under natural rainfall and simulated overland flow conditions. The soil detachment rate, runoff shear stress and stream power exhibited the same trends as runoff and soil loss. The soil erosion characteristics varied at sites with different slope lengths, and the degree of soil erosion reached its minimum on gentle-slope land sites of 30 or 40 m. Therefore, 30-40 m slope lengths may be the recommended range to control soil loss from newly reconstructed gentle-slope lands. The conclusions of this study provide theoretical guidance for farming plot construction engineering, which can promote the sustainable development of cultivated land resources in hilly mountainous regions.

Sedimentary chronology reinterpreted from Changshou Lake of the Three Gorges Reservoir Area reveals natural and anthropogenic controls on sediment production.

Sedimentary archives preserved in geomorphic sinks provide records of historical sediment dynamics and its related natural and anthropogenic controls. This study reinterpreted sedimentary processes in Changshou Lake of the Three Gorges Reservoir Area in China by combining a rainfall erosivity index with multiple tracing proxies, and the impacts of natural and anthropogenic drivers on sediment production were also explored. Erosive rainfalls with low frequency and large magnitude in the rainy season contribute to a substantial proportion of annual total rainfall, which thus can be used to infer erosion and sediment yield events. The sedimentary chronology was determined by comparing rainfall erosivity index with depth distribution of 137Cs and absolute particle size, which revealed annual sedimentation rates ranging from 1.1 to 2.3 cm a-1. The multi-proxy dating index and variation of sedimentation rate divided the sediment profile into three major periods. The reference period (1956-1982) displays low variability of TOC, TN, trace metal concentrations, and mean sedimentation rate. In the stressed period (1982-1998), industrial and sewerage discharge led to input and deposition of TOC, TN, and trace metals (e.g., Cd, Co, Cu, Cr, and Ni). The highest annual sediment accumulation rate of 2.3 cm a-1 may be ascribed to the 1982 big flood event. In the present period (1998-2013), increased TOC, TN and decreased trace metals in the top layers of the sediment core indicated changes in lake ecology. Fish farming promoted algal growth and primary productivity which caused eutrophication until 2004-2005. The reduced mean sedimentation rate of 1.7 cm a-1 between 1998 and 2004, and thereafter, may be attributed to soil and water conservation and reforestation policies implemented in the Longxi catchment. Human activities such as deforestation, cultural and industrial revolution, and lake eutrophication associated with fish farming since 1989, therefore led to appreciable limnological variations. Overall, the dated sedimentary profile from Changshou Lake displays high consistency with archived historical events and reflects the impact of both natural and anthropogenic controls on sediment production.

Linking sedimentary total organic carbon to 210Pbex chronology from Changshou Lake in the Three Gorges Reservoir Region, China.

The influences of total organic carbon (TOC) and total nitrogen (TN) on Lead-210 (210Pb) dating have recently been of increasing concern in lacustrine research. Sediment core from Changshou Lake in the Longxi catchment was investigated for influence of TOC on 210Pb dating. Lead-210 excess (210Pbex), Cesium-137 (137Cs) activities, TOC, TN, and particle size were measured. We proposed a dating index based on 137Cs chronology and particle size distribution of the lake sediment profile and rainfall erosivities calculated from Longxi catchment metrological records. Increasing trends in TOC and TN were specifically caused by commercial cage fish farming after 1989. The statistically significant correlation between 210Pbex activity, TOC (0.61, p = 0.04) and TN (0.51, p = 0.04), respectively explained post-1989 210Pb scavenging. The 210Pbex activity was closely related with coupled peaks of TOC and TN from mass depth 5-10 g cm-2. Higher TOC/TN ratio (8.33) indicated submerged macrophytes and native aquatic algal growth as main source of carbon from enhanced primary productivity because of massive fertilizer use and coherent climate warming. The study supported key hypothesis on vital role of fertilizer usage and algal derived TOC in controlling sedimentary 210Pbex activity at Changshou Lake sediment. 137Cs profile and erosive events as time markers provided reliable and consistent sedimentation rate of (1.6 cm y-1). 210Pbex activity decayed exponentially after peak at mass depth 5.68 g cm-2. Therefore, violation of 210Pb dating primary assumptions made it inappropriate for sediment dating at Changshou Lake. TOC content must be considered while using 210Pb as dating tool for lake sediment profiles.

[Characteristics of Deposited Sediment and Assessment of Heavy Metals in Typical Tributaries Bay Riparian Zone of the Three Gorges Reservoir].

In order to analyze the spatial variation characteristics of grain diameter, nutrient elements and heavy metal pollution with deposition sediment in tributaries bay of the Three Gorges Reservoir, we selected 9 typical tributaries bay, 54 deposited sediment samples were collected from the riparian zone for analyzing grain diameter distribution, capacity, organic matter, nutrient elements of TN, TP and K, heavy metal elements of Cr, Cu, Ni, Pb, and Zn. The results indicated that particle size distribution from Wujiang River in Fuling to the Modao stream in Yunyang presented a trend of fluctuation, deposited sediment at 160-165 m elevation was coarser than that at 165-175 m elevation,volume percent of sand and clay presented a moderate variation at both altitudes, while silt had small variation. Independent sample t test showed that characteristics difference between the upper and lower sediments in riparian zone was not significant. The geo-accumulation index of heavy metal pollutants in the sediment from riparian zone of the Three Gorges Reservoir tributaries bay indicated that, only Zn element in Zhenxi River, Longdong River and Long River, Pb element in the Modao Stream belonged to non-moderate pollution levels, whereas there were no pollution of all other elements in tributaries.

Comparison of the soil losses from (7)Be measurements and the monitoring data by erosion pins and runoff plots in the Three Gorges Reservoir region, China.

The potential for using (7)Be measurements to document soil redistribution associated with a heavy rainfall was estimated using (7)Be method on a bare purple soil plot in the Three Gorges Reservoir region of China. The results were compared with direct measurement from traditional approaches of erosion pins and runoff plots. The study shows that estimation of soil losses from (7)Be are comparable with the monitoring results provided by erosion pins and runoff plots, and are also in agreement with the existing knowledge provided by 137Cs measurements. The results obtained from this study demonstrated the potential for using (7)Be technique to quantify short-term erosion rates in these areas.