Fluorescent tag reveals the potential mechanism of how indigenous soil bacteria affect the transfer of the wild fecal antibiotic resistance plasmid pKANJ7 in different habitat soils

Biofilm formation mechanisms of mixed antibiotic-resistant bacteria in water: Bacterial interactions and horizontal transfer of antibiotic-resistant plasmids

Over 95 % of bacteria on water supply pipeline surfaces exist in biofilms, which are hotspots for antibiotic resistance gene (ARG) transmission. This study established mixed biofilm culture systems on a metal iron substrate using Escherichia coli: antibiotic-sensitive bacteria (ASB) and antibiotic-resistant bacteria (ARB). The growth rate and extracellular polymeric substances (EPS) content of mixed biofilm surpassed single-species biofilms due to synergistic interactions among different bacteria. However, the composition of mixed biofilms formed by ASB and ARB became unstable after 72 h, linked to reduced polysaccharide proportions in EPS and inter-bacterial competition. The bacterial composition and conjugative transfer frequency of ARGs in mixed biofilms indicate that biofilm formation significantly enhances horizontal transfer of ARGs. Notably, the conjugative transfer frequency of the mixed biofilm formed by two ARB increased 100-fold within five days. In contrast, the conjugative transfer frequency in the mixed biofilm formed by ASB and ARB was unstable; inter-bacterial competition led to plasmid loss associated with horizontal transfer of ARGs, ultimately resulting in biofilm shedding. Furthermore, genes associated with ARG transfer and biofilm growth up-regulated by 1.5 - 6 and 2 - 7 times, respectively, in mixed biofilm. These findings highlight a mutually reinforcing relationship between biofilm formation and horizontal ARG transmission, with significant environmental implications.

Development of a 3-step sequential extraction method to investigate the fraction and affecting factors of 21 antibiotics in soils

Antibiotic exist in various states after entering agricultural soil through the application of manure, including the aqueous state (I), which can be directly absorbed by plants, and the auxiliary organic extraction state (III), which is closely associated with the pseudo-permanence of antibiotics. However, effective analytical methods for extracting and affecting factors on fractions of different antibiotic states remain unclear. In this study, KCl, acetonitrile/Na2EDTA-McIlvaine buffer, and acetonitrile/water were successively used to extract states I, II, and III of 21 antibiotics in soil, and the recovery efficiency met the quantitative requirements. Random forest classification and variance partitioning analysis revealed that dissolved organic matter, pH, and organic matter were important factors affecting the recovery efficiency of antibiotic in states I, II, and III, respectively. Additionally, 65-day spiked soil experiments combined with Mantel test analysis suggested that pH, organic acids, heavy metals, and noncrystalline minerals differentially affected antibiotic type and state. Importantly, a structural equation model indicated that organic acids play a crucial role in the fraction of antibiotic states. Overall, this study reveals the factors influencing the fraction of different antibiotic states in soil, which is helpful for accurately assessing their ecological risk.