Erwinia amylovora causes fire blight in economically important plants of the family Rosaceae. This bacterial pathogen spends part of its life cycle coping with starvation and other fluctuating environmental conditions. In many Gram-negative bacteria, starvation and other stress responses are regulated by the sigma factor RpoS. We obtained an E. amylovora rpoS mutant to explore the role of this gene in starvation responses and its potential implication in other processes not yet studied in this pathogen. Results showed that E. amylovora needs rpoS to develop normal starvation survival and viable but nonculturable (VBNC) responses. Furthermore, this gene contributed to stationary phase cross-protection against oxidative, osmotic, and acid stresses and was essential for cross-protection against heat shock, but nonessential against acid shock. RpoS also mediated regulation of motility, exopolysaccharide synthesis, and virulence in immature loquats, but not in pear plantlets, and contributed to E. amylovora survival in nonhost tissues during incompatible interactions. Our results reveal some unique roles for the rpoS gene in E. amylovora and provide new knowledge on the regulation of different processes related to its ecology, including survival in different environments and virulence in immature fruits.
The extensive range of applications where synthetic nanomaterials are nowadays used is causing a huge commercial market. An incipient use of these nanomaterials arises from the need to generate alternative antimicrobial agents, anticipating the development of resistant microorganisms. Here, we show a nanostructured ZnO with antimicrobial properties and low-cytotoxicity based on a nanoparticles arrangement by controlling the formation of sintering-neck into nanoporous spheres. The antimicrobial effectiveness of ZnO spheres is tested in a broad-spectrum of microorganisms such as fungi, Gram-negative and Gram-positive bacteria. The hierarchical structures show highly effective antimicrobial activity at low concentrations and in relatively short action times (24-72h). We demonstrate that the enhanced antimicrobial properties against microorganisms are ascribed to a combining of both physical and chemical interactions between microorganism and ZnO. The approximation mechanism between microorganism and ZnO is provided through electrostatic forces (physical interaction) which, thanks to the ZnO-microorganism proximity, promote a rapid release of zinc cations and the reactive oxygen species penetration into microorganisms (chemical interaction). We believe that this work provides insights on the mechanisms underlying the interactions ZnOmicroorganism and possess a combined action mechanism for which nanostructured ZnO is so effective to combat microorganisms.
This article reports the excellent antimicrobial response of nanoparticulate ZnO against multidrug-resistant organisms (MDROs). We demonstrate that the enhanced antimicrobial activity against MDROs depends on the crystalline defects of ZnO. Hence, this work provides insights on the ZnO-microorganism interactions, and we pose combined physico-chemical action mechanisms against resistant bacteria.
Highlights-Synthesis of ZnO nanoparticles with antimicrobial response against multidrug-resistant organisms.-A high crystal defect concentration leads to a high surface reactivity and they improve the antibacterial response -A combined action of surface reactivity is mandatory to obtain this inorganic antimicrobial agent.
In the last few years, the rapid and continuing emergence of antibiotic resistance for microbial pathogens has questioned the future utility of antibiotics. Thus, the discovery of new antimicrobials is highly desired to fight microorganisms with multi-drug resistant capability. Here, we have used an inorganic UV filter as a model system to investigate the behaviour of a new preservative, based on Ag-Zn cations, to replace parabens in sunscreens. The new glass preservative is incorporated to the UV filter composite by using an easy and eco-friendly method based on a dry nanodispersion. The Challenge Test clearly demonstrates a robust toxicity towards microorganisms both the resistant bacteria and the fungi. This stimulant behavior can be explained by coupling between the antimicrobial activity of the Ag + and the antifungal activity of Zn +2. Importantly, leaching assays show that the controlled released of these cations over time results in a long-lasting antimicrobial property, pointing out that this material is a promising paraben-free candidate.
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