Foodborne bacteria can pose a threat to the public health due to their spoilage and virulence potential, which can be regulated by quorum sensing (QS) system. In the study, we isolated a spoilage bacteria strain Aeromonas salmonicida GMT3 from refrigerated sturgeon. The complete genome of A. salmonicida GMT3 was sequenced, and the QS related genes were assigned. QS signal molecules N-acyl-homoserine lactones (AHLs) and AI-2 were detected. Genes regulating the spoilage-related metabolic pathways, including protease and lipase secretion, amines metabolism, sulfur metabolism, motility and biofilm formation were analyzed. Furthermore, genes encoding for several virulence factors, e.g. hemolysin, aerolysin, type II secretion system (T2SS), type VI secretion system (T6SS), antibiotic and multidrug resistance were also identified. In addition, the spoilage and virulence phenotypes associated with QS including protease, swimming and swarming activity, biofilm and hemolytic activity were detected. This study provided new insights into spoilage and virulence mechanisms correlated with QS of A. salmonicida GMT3, which might promote development of new approaches for spoilage and virulence control based on QS target.

Bacterial quorum sensing (QS) is a process in which bacteria conduct chemical communication through the production, release, accumulation and induction of signaling molecules called autoinducers (AI). Aeromonas is a common spoilage bacterium in aquatic products, and also a conditional pathogenic bacterium in animals and humans. In recent years, studies have reported that the pathogenicity and spoilage behavior of Aeromonas may be related to QS, suggesting that it can be prevented and controlled by inhibiting the QS. Aeromonas has three QS systems including AI-1 system with N-acyl homoserine lactones (AHLs) as signaling molecules, AI-2 system with 4,5-dihydroxy 2,3-pentanedione (DPD) derivatives as signaling molecules and AI-3 system regulated by QseBC. This paper introduces these three QS systems and their regulation mechanisms in detail. Furthermore, this paper focuses on recent progress in research on plant-derived, microbe- and animal-derived and chemically synthesized QS inhibitors (QSI) of Aeromonas. The potential application of QSI to the prevention of aquatic product spoilage and aquatic diseases caused by Aeromonas is discussed in order to provide a reference for the application of Aeromonas QSI in aquatic product safety.

微生物的群体感应(quorum sensing,QS)广泛存在于发酵蔬菜中,其调控着蔬菜的发酵进程,影响了发酵蔬菜的产品质量;群体感应抑制剂(quorum sensing inhibitors,QSI)通过干扰微生物的 QS系统来调控食品的腐败变质,对延长食品保质期具有重大的意义.因此,该研究以四川泡菜为研究对象,选择了群体感应抑制剂D-核糖,研究其对外源添加腐败菌阴沟肠杆菌(Enterobacter cloacae)、克雷伯氏杆菌(Klebsiella Trevisan)、普罗维斯登菌(Providencia ewing)和弗氏柠檬酸杆菌(Citrobacter freundii)的泡菜的影响,研究结果表明,D-核糖处理后,泡菜膜醭的形成受到显著抑制并且有效维持了泡菜成熟时的pH.该研究进一步揭示了D-核糖处理后对单一腐败菌的生长、AI-2 活性以及生物被膜的影响.结果表明,D-核糖处理后,在不影响腐败菌生长的情况下生物被膜的形成、AI-2 的活性均受到抑制;扫描电镜发现,D-核糖处理后各腐败菌无法形成紧密的生物被膜,呈现单菌形式分布.以上结果将为开发新型泡菜防腐保鲜剂提供新的思路.

Pickles are typical traditional Chinese fermented vegetables. Complex microbiota interacts throughout the fermentation and deterioration process. Minimal studies are available involving quorum sensing (QS) signaling in pickles. This study investigated the changes in the general pickle properties and microbial diversity at 4 d, 31 d, and 79 d. The QS signaling activity of various strains isolated at these key time points was screened using biosensor strains, while the types of signal molecules were further identified using UHPLC/QTOF-MS/MS. At 4 d, Lactobacillus represented the dominant genus, while Lactobacillus plantarum was identified as the bacteria with AI-2-producing ability. At 31 d, the dominant genus was also Lactobacillus, while the relative abundance of Pediococcus displayed a distinct increase. At this time point, L. plantarum represented the AI-2-producing bac-teria, followed by Lactobacillus brevis, Pediococcus sp., Enterobacter sp., and Bacillus megaterium. At 79 d, Lacto-bacillus was displaced by Enterobacter as the dominant microorganisms, while the AI-2-producing bacteria were identified as L. plantarum, Enterobacter sp., B. megaterium, Klebsiella sp., and Staphylococcus sp. Moreover, AHL activity was only present in isolates from the 79-d brine and was identified as C4-HSL and C6-HSL. In addition, the luxS gene was amplified via cDNA reversely transcription from the total RNA extracted from the brine at all three time points using the L. plantarum luxS primers. The AHL-related genes were only amplified in the RNA of 79-d brine samples using Klebsiella pneumoniae- and Bacillus cereus-related primers. This study presented theo-retical references for QS during pickle fermentation and deterioration.

The quality of pickled vegetables is essentially safeguarded through various processing techniques. In this study the effects of high hydrostatic pressure processing (HPP), pasteurization (Pt), nisin, HPP + nisin and Pt + nisin on fermented radishes (Raphanus sativus L.) were compared. The effects of the different treatments on firmness were not immediately apparent, however, the HPP-treated pickles maintained their hardness best during storage. Compared with Pt, the non-thermal treatments were found to have moderate effects on the colors, both immediately after treatment and during storage. Both HPP and Pt reduced microbes, while HPP + nisin completely inactivated bacteria. The activities of polyphenol oxidase (PPO), peroxidase (POD) and pectin methylesterase (PME) were most inactivated via Pt, followed the action of HPP and then by that of the nisin. The sensory evaluation suggested that non-thermal pickled radish might be better accepted by consumers. Moreover, Pt had the strongest ability to reduce oxalic acid and sulfur-containing compounds, while the effects of HPP were relatively moderate, and HPP not only effectively reduced sulfur-containing compounds, but also helped to retain the favorable factors in the pickles. The findings of this study, thus, indicate that HPP could be a promising alternative to traditional pasteurization in the processing and storage of fermented vegetables.

The persistence of Staphylococcus aureus within biofilm can lead to contamination of medical devices and life-threatening infections. Luckily, lactic acid bacteria (LAB) have an inhibitory effect on the growth of these bacteria. This study aims to select LAB strains from fermented vegetables, and analyze their potential inhibition activities against S. aureus. In total, 45 isolates of LAB were successfully isolated from Sichuan pickles, and the CFS of Lactiplantibacillus plantarum LR-14 exerted the strongest inhibitory effect against S. aureus. Moreover, S. aureus cells in planktonic and biofilm states both wrinkled and damaged when treated with the CFS of L. plantarum LR-14. In addition, whole genome sequencing analysis indicates that L. plantarum LR-14 contains various functional genes, including predicted extracellular polysaccharides (EPS) biosynthesis genes, and genes participating in the synthesis and metabolism of fatty acid, implying that L. plantarum LR-14 has the potential to be used as a probiotic with multiple functions.

The use of probiotics has recently become a considerably promising research area. The most advanced fourth-generation probiotics involve beneficial bacteria enclosed in biofilms. However, differences in the effects of probiotics in biofilm and those in planktonic states are, as yet, unclear. In this study, it was ascertained that the biofilm mode of Lactobacillus paraplantarum L-ZS9 had a comparatively higher density and stronger resistance. Untargeted metabolomics analysis suggested a significant distinction between planktonic and biofilm cells, with amino acids and carbohydrate metabolism both more active in the biofilm mode. Furthermore, the in vivo experiment showed that the biofilm strain displayed better immunomodulation activity, which could increase the relative abundance of Lactobacillus in the intestinal microbiota of dogs. The relative abundance of intestinal microbiota participating in carbohydrate metabolism was higher in the biofilm probiotic-treated dogs. Correlation analysis between L-ZS9-producing metabolites, dog intestinal microbiome diversity and dog blood immune indexes (sIgA or IgG) revealed the interaction between these three components, which might explain the mechanisms by which biofilm L-ZS9 regulated the intestinal microbiome and immunity activity of the host, through the production of various metabolites. Findings of this study will, thus, enhance understanding of the beneficial effects of biofilm probiotics, as well as provide references for further investigation.

This study aimed to investigate whether and how pgm,fba,and gap overexpression can affect the stress resistance,adhesiveness,and biofilm formation of Lactobacillus plantarum LR-1.Results showed that the overexpression of the pgm and fba genes enhanced the heat,acid and bile salt resistance,biofilm formation and adhesiveness of L.plantarum LR-1.The transcriptional level of the gap gene had no significant effect on the stress resistance,biofilm formation or adhesiveness.The up-regulation of pgm,fba,and gap increased the transcriptional levels of tuf and luxS in this strain with the first two being more effective than the last one.Furthermore,bioinformatic analyses suggested that pgm and fba could be associated with genes related to multiple pathways.These results provide a new understanding of the role of glycolytic pathway-related genes in regulating the stress resistance,adhesiveness,and biofilm formation of L.plantarum.