Loureirin A is a narrow-spectrum antimicrobial agent against Helicobacter pylori.

Currently, Helicobacter pylori eradication by antibiotic therapy faces various challenges, including antibiotic resistance, side effects on intestinal commensal bacteria, and patient compliance. In this study, loureirin A (LrA), a traditional Chinese medicine monomer extracted from Sanguis Draconis flavones, was found to possess specific antibacterial activity against H. pylori without the bacteria displaying a tendency to develop resistance in vitro. LrA demonstrated a synergistic or additive effect when combined with omeprazole (a proton pump inhibitor) against H. pylori. The combination of LrA and omeprazole showed promising anti-H. pylori potential, exhibiting notable in vivo efficacy comparable to standard triple therapy in mouse models infected with both drug-sensitive and drug-resistant H. pylori strains. Moreover, the narrow-spectrum antibacterial profile of LrA is reflected in its minimal effect on the diversity and composition of the mouse gut microbiota. The underlying mechanism of action of LrA against H. pylori involves the generation of bactericidal levels of reactive oxygen species, resulting in apoptosis-like cell death. These findings indicate that LrA is a promising lead compound targeting H. pylori without harming the commensal bacteria.

Killing of Staphylococcus aureus persisters by a multitarget natural product chrysomycin A.

Staphylococcus aureus poses a severe public health problem as one of the vital causative agents of healthcare- and community-acquired infections. There is a globally urgent need for new drugs with a novel mode of action (MoA) to combat S. aureus biofilms and persisters that tolerate antibiotic treatment. We demonstrate that a benzonaphthopyranone glycoside, chrysomycin A (ChryA), is a rapid bactericide that is highly active against S. aureus persisters, robustly eradicates biofilms in vitro, and shows a sustainable killing efficacy in vivo. ChryA was suggested to target multiple critical cellular processes. A wide range of genetic and biochemical approaches showed that ChryA directly binds to GlmU and DapD, involved in the biosynthetic pathways for the cell wall peptidoglycan and lysine precursors, respectively, and inhibits the acetyltransferase activities by competition with their mutual substrate acetyl-CoA. Our study provides an effective antimicrobial strategy combining multiple MoAs onto a single small molecule for treatments of S. aureus persistent infections.

The RsmA RNA-Binding Proteins in Pseudomonas syringae Exhibit Distinct and Overlapping Roles in Modulating Virulence and Survival Under Different Nutritional Conditions.

The post-transcriptional regulator RsmA globally controls gene expression in bacteria. Previous studies showed that RsmA2 and RsmA3 played critical roles in regulating type III secretion system (T3SS), motility, syringafactin, and alginate productions in Pseudomonas syringae pv. tomato strain DC3000 (PstDC3000). In this study, we investigated global gene expression profiles of the wild-type PstDC3000, the rsmA3 mutant, and the rsmA2/A3 double mutant in the hrp-inducing minimum medium (HMM) and King's B (KB) medium. By comparing the rsmA2/A3 and rsmA3 mutants to PstDC3000, a total of 1358 and 1074 differentially expressed genes (DEGs) in HMM, and 870 and 1463 DEGs in KB were uncovered, respectively. When comparing the rsmA2/A3 mutant with the rsmA3 mutant, 277 and 741 DEGs in HMM and KB, respectively, were revealed. Transcriptomic analysis revealed that the rsmY, rsmZ, and rsmX1-5 non-coding small RNAs (ncsRNAs) were positively affected by RsmA2 and RsmA3, while RsmA3 positively regulates the expression of the rsmA2 gene and negatively regulates both rsmA1 and rsmA5 gene expression. Comparative transcriptomic analysis showed that RsmA2 and RsmA3 synergistically influenced the expression of genes involved in T3SS and alginate biosynthesis in HMM and chemotaxis in KB. RsmA2 and RsmA3 inversely affected genes involved in syringafactin production in HMM and ribosomal protein biosynthesis in KB. In addition, RsmA2 played a major role in influencing genes involved in sarcosine and thiamine biosynthesis in HMM and in mannitol and phosphate metabolism in KB. On the other hand, genes involved in fatty acid metabolism, cellulose biosynthesis, signal transduction, and stress responses were mainly impacted by RsmA3 in both HMM and KB; whereas RsmA3 played a major role in controlling genes involved in c-di-GMP, phosphate metabolism, chemotaxis, and capsular polysaccharide in HMM. Furthermore, regulation of syringafactin production and oxidative stress by RsmA2 and RsmA3 was experimentally verified. Our results suggested the potential interplay among the RsmA proteins, which exhibit distinct and overlapping roles in modulating virulence and survival in P. syringae under different nutritional conditions.

Fermentation: An Unreliable Seed Treatment for Bacterial Fruit Blotch of Watermelon.

Acidovorax citrulli is a seedborne pathogen that causes bacterial fruit blotch (BFB), a global threat to watermelon production. Treating watermelon seeds to eliminate A. citrulli is a critical component of BFB management, and several strategies have been evaluated to mitigate the impact of the disease. In China, watermelon seed producers routinely incubate seeds in watermelon juice (fermentation) to reduce the risk of seed infection by A. citrulli and seedling transmission of BFB. However, there has been limited effort to evaluate the efficacy of fermentation in mitigating A. citrulli seed infection. The current study showed that fermented watermelon fruit juice could inhibit A. citrulli population growth and demonstrated that the low pH conditions, not the temperature dynamic, generated during fermentation might play a major role in A. citrulli growth inhibition and could induce the viable but nonculturable (VBNC) state in A. citrulli. We developed an effective method that was based on propidium monoazide PCR to detect viable A. citrulli cells under low pH conditions or in fermented watermelon fruit juice. We also provided evidence that VBNC A. citrulli cells induced by fermented watermelon fruit juice could not be resuscitated and did not retain their virulence on watermelon seedlings. However, VBNC A. citrulli cells could be resuscitated in Luria-Bertani medium. Based on these observations, we conclude that fermentation in watermelon fruit juice may not be an effective seed treatment for BFB because it may increase the seed infection by A. citrulli.

Homologues of the RNA binding protein RsmA in Pseudomonas syringae pv. tomato DC3000 exhibit distinct binding affinities with non-coding small RNAs and have distinct roles in virulence.

Pseudomonas syringae pv. tomato DC3000 (PstDC3000) contains five RsmA protein homologues. In this study, four were functionally characterized, with a focus on RsmA2, RsmA3 and RsmA4. RNA electrophoretic mobility shift assays demonstrated that RsmA1 and RsmA4 exhibited similar low binding affinities to non-coding small RNAs (ncsRNAs), whereas RsmA2 and RsmA3 exhibited similar, but much higher, binding affinities to ncsRNAs. Our results showed that both RsmA2 and RsmA3 were required for disease symptom development and bacterial growth in planta by significantly affecting virulence gene expression. All four RsmA proteins, especially RsmA2 and RsmA3, influenced γ-amino butyric acid utilization and pyoverdine production to some degree, whereas RsmA2, RsmA3 and RsmA4 influenced protease activities. A single RsmA, RsmA3, played a dominant role in regulating motility. Furthermore, reverse transcription quantitative real-time PCR and western blot results showed that RsmA proteins, especially RsmA2 and RsmA3, regulated target genes and possibly other RsmA proteins at both transcriptional and translational levels. These results indicate that RsmA proteins in PstDC3000 exhibit distinct binding affinities to ncsRNAs and have distinct roles in virulence. Our results also suggest that RsmA proteins in PstDC3000 interact with each other, where RsmA2 and RsmA3 play a major role in regulating various functions in a complex manner.

Loss-of-Function Mutations in the Dpp and Opp Permeases Render Erwinia amylovora Resistant to Kasugamycin and Blasticidin S.

Extensive use of the antibiotic streptomycin to control fire blight disease of apples and pears, caused by the enterobacterial plant pathogen Erwinia amylovora, leads to the development of streptomycin-resistant strains in the United States and elsewhere. Kasugamycin (Ksg) has been permitted to be used as an alternative or replacement to control this serious bacterial disease. In this study, we investigated the role of two major peptide ATP-binding cassette transporter systems in E. amylovora, the dipeptide permease (Dpp) and oligopeptide permease (Opp), in conferring sensitivity to Ksg and blasticidin S (BcS). Minimum inhibitory concentration and spot dilution assays showed that the dpp deletion mutants exhibited slightly enhanced resistance to Ksg in rich medium, whereas the opp mutant exhibited slightly enhanced resistance to Ksg in minimal medium and BcS in rich medium. Deletion of both dpp and opp conferred a higher level of resistance to Ksg in both rich and minimal media, whereas deletion of opp alone was sufficient to confer high level of resistance to BcS in minimal medium. In addition, bioinformatic analysis combined with reverse transcription-quantitative polymerase chain reaction showed that the Rcs phosphorelay system negatively regulates opp expression and the rcsB mutant was more sensitive to both Ksg and BcS in minimal medium as compared with the wild type. An electrophoresis motility shift assay further confirmed the direct binding of the RcsA/RcsB proteins to the promoter region of the opp operon. However, neither the Dpp nor the Opp permeases contributed to disease progress on immature pears, hypersensitive response on tobacco leaves, or exopolysaccharide amylovoran production. These results suggested that Ksg and BcS employ the Dpp and Opp permeases to enter E. amylovora cells and the Dpp and Opp permeases act synergistically for illicit transport of antibiotics.