Decreased cyclic-AMP caused by ATP contributes to fosfomycin heteroresistance in avian Escherichia coli.

BACKGROUND: Fosfomycin is an important broad-spectrum bactericidal antibiotic to treat multidrug-resistant bacteria infections. It is generally accepted that heteroresistant bacteria are an intermediate stage in the formation of drug resistance, but there are few studies on the formation mechanism underlying fosfomycin heteroresistance (FHR). OBJECTIVES: To reveal the characteristics and formation mechanisms of FHR in Escherichia coli isolates obtained from chickens. METHODS: We identified the FHR according to the population analysis profile (PAP) test and in vitro time-kill assay. Growth curves for FHR E. coli and their subpopulations were measured. Also, the subpopulations were repeatedly cultured in fosfomycin-free medium for 5-20 overnight incubation periods. The formation mechanisms of FHR in E. coli isolates were identified through accumulation assay, carbohydrate utilization testing, real-time relative quantitative PCR analysis, DNA sequencing, transcriptomic analysis, intracellular ATP and cAMP-level assessment. RESULTS: Four of six E. coli strains were confirmed to show FHR, with a total of six subpopulations. The subpopulations restored phenotypic susceptibilities to fosfomycin within 5-20 overnight incubation sessions, but four of six subpopulations still maintained FHR characteristics. Differing from their parental isolates, the uptake of fosfomycin in the subpopulations through GlpT was reduced remarkably. Further studies identified that the low expression of glpT was due to the decrease of intracellular cAMP levels in the subpopulations, which was caused by the decreased ATP levels in cells. CONCLUSIONS: Our findings revealed the formation mechanism of E. coli isolates showing FHR obtained from chicken in China and characterized the dynamic change traits in vitro of the subpopulations.

Transferable Active Centers of Strongly Coupled MoS2@Sulfur and Molybdenum Co-doped g-C3N4 Heterostructure Electrocatalysts for Boosting Hydrogen Evolution Reaction in Both Acidic and Alkaline Media.

Designing an excellent acidic and alkaline general-purpose hydrogen evolution electrocatalyst plays an important role in promoting the development of the energy field. Here, a feasible strategy is reported to use the strongly coupled MoS2@sulfur and molybdenum co-doped g-C3N4 (MoS2@Mo-S-C3N4) heterostructure with transferable active centers for catalytic reactions in acidic and alkaline media. Research studies have shown that the unsaturated S site at the edge of MoS2 and the active N atom on the Mo-S-C3N4 substrate are, respectively, the active centers of acidic and alkaline hydrogen evolution reaction. Specifically, Mo-S-C3N4 is regarded as a synergistic catalyst for the active species MoS2 in acidic hydrogen evolution, while MoS2 acts as a co-catalyst when the alkaline active species are transferred to Mo-S-C3N4. The coordination of the electrons between the interfaces achieves a synergistic balance, which provides the optimal sites for the adsorption of the reactants. Such an electrocatalyst exhibits overpotentials of 193 and 290 mV at 10 mA cm-2 in 0.5 M H2SO4 and 1 M KOH, respectively, which was better than numerous previous reports. This research provides an outstanding avenue to realize multifunctional electrocatalysts.