Eugenol, the major active essential oil component of clove, was reported to possess QS (quorum sensing) inhibitory activity. A previous study found that eugenol could bind to quorum sensing receptors of Pseudomonas aeruginosa and down-regulate the expression of Streptococcus mutans virulence genes at sub-MIC (minimum inhibitory concentration) without affecting the bacterial growth. However, the alterations of QS signal molecules at transcription levels was not well understood. To better understand interactions of Klebsiella pneumoniae in response to eugenol and explore molecular regulations, transcriptome sequencing was performed. A total of 5779 differentially expressed genes (DEGs) enriched in a variety of biological processes and pathways were identified. The transcriptional data was validated by qPCR and the results showed that the expression profiles of 4 major genes involved in autoinducers-2 (AI-2) synthesis, including luxS, pfs, and lsrK were consistent with transcriptome analysis except for lsrR, a transcriptional repressor gene of lsr operon, which may repress the expression of following genes responsible for AI-2 signal transmission in vivo. In vitro AI-2 synthesis assay also revealed that eugenol could inhibit AI-2 generation. The results of our study offer insights into the mechanisms of QS inhibitory activity and K. pneumoniae AI-2 alterations after eugenol treatment.

Summary: Pseudomonas sp. strain 166 was isolated from soil samples from Changbai Mountains. A novel bacteriocin PA166 from Pseudomonas sp. 166 was purified using ammonium sulfate, dextran gel chromatography column and Q‐Sepharose column chromatography successively. The molecular mass of bacteriocin PA166 was found to be 49.38 kDa by SDS‐PAGE and liquid chromatography–mass spectrometry (MS)/MS. Bacteriocin PA166 showed stability at a wide range of pH (2–10), and thermal stability (40, 60, 80 and 100°C). The bacteriocin PA166 antimicrobial activity was slightly inhibited by Ca ²⁺ , K ⁺ and Mg ²⁺ . The minimum bactericidal concentrations of bacteriocin PA166 against five Pasteurella multocida strains ranged from 2 to 8 μg ml ⁻¹ . Bacteriocin PA166 showed low cytotoxicity and a higher treatment index (TI = 82.51). Fluorescence spectroscopy indicated that bacteriocin PA166 destroyed the cell membrane to exert antimicrobial activity. In summary, bacteriocin PA166 had strong antibacterial activity, high TI and low toxicity, and hence could serve as a potential clinical therapeutic drug.

To evaluate the antimicrobial resistance and virulence gene characteristics of highly pathogenic Proteus mirabilis. In this study, we isolated P. mirabilis CC15031 from diarrhea dogs in China, tested the median lethal dose (LD₅₀), and measured the minimum inhibitory concentration (MIC) of 10 different antibiotics commonly used in veterinary clinic. Meanwhile, we presented the complete genome sequence annotations to analyze the virulence and resistance formation mechanism. The results showed that the CC15031 presented relatively potent pathogenicity in mice (LD₅₀ = 0.57 × 10⁶ CFU) and exhibited a high degree of resistance to all the tested antimicrobial agents. The CC15031 genome of 4,031,742 bp with 3,745 predicted genes had an average gene length of 917 bp and 38.99% guanine-cytosine content. A new variant of an integrative and conjugative element with a type IV secretion system (217,446 bp) conferring multidrug resistance was identified and characterized by structural analysis in CC15031. These data provide a foundation for understanding the genomic features and antimicrobial resistance mechanisms of this pathogen.