The probiotic fermented milk of Lacticaseibacillus paracasei JY062 and Lactobacillus gasseri JM1 alleviates constipation via improving gastrointestinal motility and gut microbiota.

Constipation is directly related to the intestinal microenvironment, in which the promotion of gastrointestinal (GI) motility and improvement of gut microbiota distribution are important for alleviating symptoms. Herein, after the intervention of probiotic fermented milk (FMMIX) containing Lacticaseibacillus paracasei JY062 and Lactobacillus gasseri JM1 for 14 d in Kunming mice with loperamide-induced constipation, the results indicated that FMMIX significantly increased the secretion of serum motilin, gastrin and 5-hydroxytryptamine, as well as decreased the secretion of peptide YY, vasoactive intestinal peptide, and nitric oxide in mice. As determined by immunohistochemical analysis, FMMIX promoted an augmentation in the quantity of Cajal interstitial cells. In addition, the mRNA and protein expression of c-kit and stem cell factor (SCF) were upregulated to facilitate intestinal motility. High-throughput sequencing and gas chromatography techniques revealed that FMMIX led to an increase in the relative abundance of beneficial bacteria (Lactobacillus, Oscillospira, Ruminococcus, Coprococcus, and Akkermansia), reduced the presence of harmful bacteria (Prevotella), and resulted in elevated levels of short-chain fatty acids (SCFA) with a superior improvement compared with unfermented milk. Untargeted metabolomics revealed significant upregulation of functional metabolites such as l-pipecolinic acid, dl-phenylalanine, and naringenin in FMMIX, presumably playing a potential role in constipation relief. Overall, our results showed that FMMIX had the potential to alleviate constipation symptoms in mice by improving the secretion of serum GI regulatory peptides and neurotransmitters, increasing the expression of c-kit and SCF proteins, and modulating the gut microbiota structure and SCFA levels, and may be associated with an increase in these functional metabolites. This suggested that FMMIX could be a promising adjunctive strategy for managing constipation symptoms and could contribute to the development of functional foods aimed at improving gut health.

Optical nanosensors based on noble metal nanoclusters for detecting food contaminants: A review.

Food contaminants present a significant threat to public health. In response to escalating global concerns regarding food safety, there is a growing demand for straightforward, rapid, and sensitive detection technologies. Noble metal nanoclusters (NMNCs) have garnered considerable attention due to their superior attributes compared to other optical materials. These attributes include high catalytic activity, excellent biocompatibility, and outstanding photoluminescence properties. These features render NMNCs promising candidates for crafting nanosensors for food contaminant detection, offering the potential for the development of uncomplicated, swift, sensitive, user-friendly, and cost-effective detection approaches. This review investigates optical nanosensors based on NMNCs, including the synthesis methodologies of NMNCs, sensing strategies, and their applications in detecting food contaminants. Furthermore, it involves a comparative assessment of the applications of NMNCs in optical sensing and their performance. Ultimately, this paper imparts fresh perspectives on the forthcoming challenges. Hitherto, optical (particularly fluorescent) nanosensors founded on NMNCs have demonstrated exceptional sensing capabilities in the realm of food contaminant detection. To enhance sensing performance, future research should prioritize atomically precise NMNCs synthesis, augmentation of catalytic activity and optical properties, development of high-throughput and multimode sensing, integration of NMNCs with microfluidic devices, and the optimization of NMNCs storage, shelf life, and transportation conditions.

Depletion of reactive oxygen species induced by beetroot (Beta vulgaris) extract leads to apoptosis-like death in Cronobacter sakazakii.

This research aimed to disclose the antibacterial activity of beetroot extract (Beta vulgaris) against Cronobacter sakazakii and its possible mechanisms. We evaluated its antibacterial activity by measuring the minimum inhibitory concentration (MIC) and time-kill kinetics. We also evaluated the intracellular ATP levels, bacterial apoptosis-like death (ALD), and reactive oxygen species (ROS) levels to reveal the possible antibacterial mechanisms. Our results showed that the MIC of beetroot extract against C. sakazakii was 25 mg/mL and C. sakazakii (approximately 8 log cfu/mL) was completely inhibited after treatment with 2 MIC of beetroot extract for 3 h. Beetroot extract reduced intracellular ATP levels and facilitated characteristics of ALD in C. sakazakii, such as membrane depolarization, increased intracellular Ca2+ levels, phosphatidylserine externalization, caspase-like protein activation, and DNA fragmentation. Additionally, and different from most bacterial ALD caused by the accumulation of ROS, beetroot extract reduced the intracellular ROS levels in C. sakazakii. Our experimental data provide a rationale for further research of bacterial ALD and demonstrate that beetroot extract can inhibit C. sakazakii in food processing environments.

Ganoderma spp. polysaccharides are potential prebiotics: a review.

The gut microbiota (GM) is a complex ecosystem that is closely linked to host health. Ganoderma spp. polysaccharides (GPs), a major bioactive component of the fungal genus Ganoderma, can modulate the GM, exhibiting various health effects and prebiotic potential. This review comprehensively concluded the structural features and extraction method of GPs. The mechanism of GPs for anti-obesity, anti-diabetes, anti-inflammatory, and anti-cancer were further evaluated. The simulated gastrointestinal digestion of GPs and the utilization mechanism of host microorganisms were discussed. It was found that the physicochemical properties and biological activities of GPs depend on their structural characteristics (molecular weight, monosaccharide composition, glycosidic bonds, etc.). Their extraction method also affects the structure and bioactivities of polysaccharides. GPs supplementation could increase the relative abundance of beneficial bacteria (e.g. Bacteroides, Parabacteroides, Akkermansia, and Bifidobacterium), while reducing that of pathogenic bacteria (e.g. Aerococcus, Ruminococcus), thus promoting health. Moreover, GPs are resistant to digestion in the stomach and small intestine but are digested in the large intestine. Therefore, GPs can be considered as potential prebiotics. However, further studies should investigate how GPs as prebiotics regulate GM and improve host health.

Nucleic acid amplification-based strategy to detect foodborne pathogens in milk: a review.

Milk contaminated with trace amounts of foodborne pathogens can considerably threaten food safety and public health. Therefore, rapid and accurate detection techniques for foodborne pathogens in milk are essential. Nucleic acid amplification (NAA)-based strategies are widely used to detect foodborne pathogens in milk. This review article covers the mechanisms of the NAA-based detection of foodborne pathogens in milk, including polymerase chain reaction (PCR), loop-mediated isothermal amplification (LAMP), recombinase polymerase amplification (RPA), rolling circle amplification (RCA), and enzyme-free amplification, among others. Key factors affecting detection efficiency and the advantages and disadvantages of the above techniques are analyzed. Potential on-site detection tools based on NAA are outlined. We found that NAA-based strategies were effective in detecting foodborne pathogens in milk. Among them, PCR was the most reliable. LAMP showed high specificity, whereas RPA and RCA were most suitable for on-site and in-situ detection, respectively, and enzyme-free amplification was more economical. However, factors such as sample separation, nucleic acid target conversion, and signal transduction affected efficiency of NAA-based strategies. The lack of simple and effective sample separation methods to reduce the effect of milk matrices on detection efficiency was noteworthy. Further research should focus on simplifying, integrating, and miniaturizing microfluidic on-site detection platforms.

The effect of optimized carbon source on the synthesis and composition of exopolysaccharides produced by Lactobacillus paracasei.

This study aimed to predict the optimal carbon source for higher production of exopolysaccharides (EPS) by Lactobacillus paracasei TD 062, and to evaluate the effect of this carbon source on the production and monosaccharide composition of EPS. We evaluated the EPS production capacity of 20 strains of L. paracasei under the same conditions. We further investigated L. paracasei TD 062, which showed the highest EPS-producing activity (0.609 g/L), by examining the associated biosynthesis pathways for EPS. Genomics revealed that fructose, mannose, trehalose, glucose, galactose, and lactose were carbon sources that L. paracasei TD 062 could use to produce EPS. We identified an EPS synthesis gene cluster that could participate in transport, export, and sugar chain synthesis, and generate 6 sugar nucleotides. Experimental results showed that the sugar content of the EPS produced using fermentation with the optimized carbon source (fructose, mannose, trehalose, glucose, galactose, and lactose) increased by 115%. Furthermore, use of the optimized carbon source changed the monosaccharide content of the associated EPS. The results of enzyme activity measurements showed significant increases in the activity of 2 key enzymes involved in the glycoside synthesis pathway. Our study revealed that optimizing the carbon source provided for fermentation not only increased the production of EPS, but also affected the composition of the monosaccharides by increasing enzyme activity in the underlying synthesis pathways, suggesting an important role for carbon source in the production of EPS by L. paracasei TD 062.

Invited review: Stress resistance of Cronobacter spp. affecting control of its growth during food production.

Members of the Cronobacter genus include food-borne pathogens that can cause infections in infants, with a mortality rate as high as 40 to 80%. The high fatality rate of Cronobacter and its isolation from numerous types of food, especially from powdered infant formula, demonstrate the serious nature of this organism. The source tracking of Cronobacter spp. and the analysis of high-frequency species from different sources are helpful for a more targeted control. Furthermore, the persistence during food processing and storage may be attributed to strong resistance of Cronobacter spp. to environment stresses such as heat, pH, and desiccation. There are many factors that support the survival of Cronobacter spp. in harsh environments, such as some genes, regulatory systems, and biofilms. Advanced detection technology is helpful for the strict monitoring of Cronobacter spp. In addition to the traditional heat treatment, many new control techniques have been developed, and the ability to control Cronobacter spp. has been demonstrated. The control of this bacteria is required not only during manufacture, but also through the selection of packaging methods to reduce postprocessing contamination. At the same time, the effect of inactivation methods on product quality and safety must be considered. This review considers the advances in our understanding of environmental stress response in Cronobacter spp. with special emphasis on its implications in food processing.

Assessment of the production of Bacillus cereus protease and its effect on the quality of ultra-high temperature-sterilized whole milk.

Bacillus cereus is one of the most important spoilage microorganisms in milk. The heat-resistant protease produced is the main factor that causes rotten, bitter off-flavors and age gelation during the shelf-life of milk. In this study, 55 strains of B. cereus were evaluated, of which 25 strains with protease production ability were used to investigate proteolytic activity and protease heat resistance. The results showed that B. cereus C58 had strong protease activity, and its protease also had the highest thermal stability after heat treatment of 70°C (30 min) and 100°C (10 min). The protease was identified as protease HhoA, with a molecular mass of 43.907 kDa. The protease activity of B. cereus C58 in UHT-sterilized whole milk (UHT milk) showed an increase with the growth of bacteria, especially during the logarithmic growth phase. In addition, the UHT milk incubated with protease from B. cereus C58 at 28°C (24 h) and 10°C (6 d) were used to evaluate the effects of protease on the quality of UHT milk, including protein hydrolysis and physical stability. The results showed that the hydrolysis of casein was κ-CN, ß-CN, and αS-CN successively, whereas whey protein was not hydrolyzed. The degree of protein hydrolysis, viscosity, and particle size of the UHT milk increased. The changes in protein and fat contents indicated that fat globules floated at 28°C and settled at 10°C, respectively. Meanwhile, confocal laser scanning microscopy images revealed that the protease caused the stability of UHT milk to decrease, thus forming age gelation.

A novel smartphone-based colorimetric aptasensor for on-site detection of Escherichia coli O157:H7 in milk.

Effective testing tools for Escherichia coli O157:H7 can prevent outbreaks of foodborne illness. In this paper, a smartphone-based colorimetric aptasensor was developed using functionalized gold nanoparticles (GNP) and multi-walled carbon nanotubes (MWCNT) for monitoring E. coli O157:H7 in milk. The maximum absorption peak of GNP bonded with aptamer (Apt) generated evident transformation from 518 to 524 nm. The excess GNP-Apt was removed by functionalized MWCNT magnetized with carbonyl iron powder (CIP) and hybridized with a DNA probe, whereas the GNP-Apt immobilized on E. coli O157:H7 remained in the system. In the presence of a high-salt solution, the GNP-Apt that captured E. coli O157:H7 remained red, but the free GNP-Apt aggregated and appeared blue. The chromogenic results were analyzed by a smartphone-based colorimetric device that was fabricated using acrylic plates, a light-emitting diode, and a mobile power pack. To our knowledge, this was the first attempt to use a smartphone-based colorimetric aptasensor employing the capture of GNP-Apt coupled with separation of MWCNT@CIP probe to detect E. coli O157:H7. The aptasensor exhibited good reproducibility and no cross-reaction for other bacteria. A concentration of 8.43 × 103 cfu/mL of E. coli O157:H7 could be tested in pure culture, and 5.24 × 102 cfu/mL of E. coli O157:H7 could be detected in artificially contaminated milk after 1 h of incubation. Therefore, the smartphone-based colorimetric aptasensor was an efficient tool for the detection of E. coli O157:H7 in milk.

An aptamer-exonuclease III (Exo III)-assisted amplification-based lateral flow assay for sensitive detection of Escherichia coli O157:H7 in milk.

Escherichia coli O157:H7 (E. coli O157:H7), one of the most widespread foodborne pathogens, can cause a series of diseases and even lead to death. In this study, a highly sensitive method was developed by combining aptamer-exonuclease III (Exo III)-assisted amplification with lateral flow assay (LFA) based on gold nanoparticles (AuNP). The compound of single-stranded (ss) DNA-anti-E. coli O157:H7 aptamer (ssDNA-aptamer) was formed by hybridization between designed target ssDNA and aptamer. When E. coli O157:H7 was present, target bacteria were bound with the aptamer, and the free target ssDNA was hybridized with the probes of the designed hairpin (HP) structure. Exo III digests the 3' double-stranded blunt end of the complex and releases the enzyme product. Because the remaining sequence of the HP of the designed enzyme product was the same as the target ssDNA sequence, the target ssDNA could be amplified. Finally, the enhanced target ssDNA was combined with AuNP-LFA to achieve visual detection of E. coli O157:H7. The quantitative ability of this platform for E. coli O157:H7 was 7.6 × 101 cfu/mL in pure culture, and the detection limit in milk was 8.35 × 102 cfu/mL. This LFA was highly specific to E. coli O157:H7, and the time for detection of E. coli O157:H7 in milk was 4 h. Hence, this system has important application prospects in the detection of pathogenic bacteria in dairy products.

Screening of specific nucleic acid targets for Cronobacter sakazakii and visual detection by loop-mediated isothermal amplification and lateral flow dipstick method in powdered infant formula.

Due to the lack of specific genes for rapid detection methods of Cronobacter sakazakii in food samples, whole genome sequence analysis was performed in this investigation using the basic local alignment search tool. Forty-two DNA fragments unique to C. sakazakii were mined, then primers were designed and screened by PCR and loop-mediated isothermal amplification (LAMP). Two primer sets, CS1 and CS31, were found as specific and stable primers, with their corresponding nucleic acid targets the CSK29544_00235 gene and CSK29544_03484 gene, respectively. Furthermore, compared with 3 genes reported previously, these 2 genes were verified as more specific to C. sakazakii among Cronobacter species, by sequence similarity alignment using Cronobacter MLST databases (http://pubmlst.org/cronobacter). The specificity of the LAMP reaction approached 100% by using 48 bacterial strains, which included 22 C. sakazakii strains. Subsequently, LAMP was combined with visual lateral flow dipstick (LFD) based on the above 2 nucleic acid targets, and was demonstrated as a rapid, efficient method with high specificity. Finally, the detection sensitivity of this assay system for pure cultures and artificially contaminated milk was measured as 4.5 × 100 cfu/mL and 5.7 × 101 cfu/g, respectively. Total time to detection for this assay was within 2 h. Thus, the establishment of this LAMP-LFD method shows great significance and potential for rapid detection of C. sakazakii in powdered infant formula.

Physicochemical and transcriptomic responses of Lactobacillus brevis JLD715 to sodium selenite.

BACKGROUND: Elemental selenium, as a new type of selenium supplement, can be prepared by microorganisms reducing inorganic selenium. In this study, Lactobacillus brevis JLD715 was incubated in broth containing different concentrations of sodium selenite (Na2 SeO3 ). RESULTS: The results showed that the bacterial biomass of L. brevis JLD715 decreased due to the inhibition of Na2 SeO3 . The cell membrane of L. brevis JLD715 treated with Na2 SeO3 was damaged, as evidenced by the reduction of intracellular ATP concentration, depolarization of cell membrane, reduction of intracellular pH and impairment of membrane integrity. In addition, we investigated the metabolism mechanism of Na2 SeO3 by L. brevis JLD715 based on transcriptome sequencing. A total of 461 genes were significantly differentially expressed under Na2 SeO3 treatment, of which 231 genes were up-regulated and 230 genes were down-regulated. These genes were involved in pathways such as pyruvate metabolism, fatty acid biosynthesis, selenocompound metabolism and nucleotide-binding oligomerization domain-like (NOD-like) receptor signaling. Meanwhile, the genes related to sulfhydryl oxidoreductase, electron carrier proteins and transmembrane transport proteins synthesis were significantly up-regulated. CONCLUSION: To sum up, the findings of this research will contribute to providing support for the application of L. brevis JLD715 in selenium-enriched functional foods. © 2021 Society of Chemical Industry.

Multiplex loop-mediated isothermal amplification-based lateral flow dipstick for simultaneous detection of 3 food-borne pathogens in powdered infant formula.

In this study, we established a rapid, simple, and sensitive method for visual and point-of-care detection of Salmonella spp., Cronobacter spp., and Staphylococcus aureus in powdered infant formula (PIF) based on multiplex loop-mediated isothermal amplification (mLAMP) combined with lateral flow dipstick (LFD). Three different species-specific target genes, siiA of Salmonella spp., internal transcribed space (ITS) of Cronobacter spp., and nuc of Staph. aureus, were applied in the mLAMP with biotin-, digoxin-, and Texas Red-modified forward inner primers and fluorescein isothiocyanate (FITC)-modified backward inner primers. After mLAMP, a large number of modified amplicons were detected with LFD; one end of the amplicon was conjugated to the anti-FITC antibody on gold nanoparticles and the other end to streptavidin (anti-digoxin or anti-Texas Red antibody) on test lines. Visual inspection of the device relies on the presence of a red band formed by accumulation of sandwich composites. The detection limits of this mLAMP-LFD assay for Salmonella spp., Cronobacter spp., and Staph. aureus in PIF without enrichment were 4.2, 2.6, and 3.4 cfu/g, respectively. The whole method can be completed in less than 1 h. Thus, mLAMP-LFD is a rapid and efficient method for simultaneously detecting Salmonella spp., Cronobacter spp., and Staph. aureus in PIF.

Electricity-free amplification and visual detection of Cronobacter species in powdered infant formula.

Due to the lack of electricity and thermostatic instruments in certain settings for convenient detection of Cronobacter species in powdered infant formula (PIF), a novel investigation was conducted to establish an electricity-free visual detection system for rapid detection of Cronobacter species in PIF. This system included a portable electricity-free heater that could use the exothermic reaction of calcium oxide and water and 3 kinds of phase change materials to supply 3 constant temperatures for immunomagnetic separation, DNA extraction, and loop-mediated isothermal amplification assay. Meanwhile, the amplified reaction combined with hydroxynaphthol blue could achieve rapid visual detection. Primers designed based on the 16S-23S ribosomal RNA internal transcribed spacer were used in loop-mediated isothermal amplification to specifically monitor Cronobacter species, and the detection limit can reach 4.2 × 102 cfu/g in PIF by an electricity-free heater in 2 h 30 min. Moreover, 2 h of pre-enrichment was necessary when the level of the PIF samples with Cronobacter spp. was 100 cfu/g. The stability of the system was evaluated in ambient temperature at 4°C, 25°C, and 37°C. The results suggested that the electricity-free heater can maintain 3 constant temperatures to support different processes. Therefore, this amplification and visual system is applicable for use in many fields for rapid and specific detection of Cronobacter species in PIF.

Lactobacillus gasseri JM1 with potential probiotic characteristics alleviates inflammatory response by activating the PI3K/Akt signaling pathway in vitro.

Lactobacillus gasseri JM1, a novel strain isolated from infant feces, exhibited common probiotic properties such as high acid tolerance, bile salt tolerance, and adhesion to epithelial Caco-2 cells, suggesting its ability to survive in the gastrointestinal tract and confer potential probiotic action on the host. In the current study, we aimed to evaluate the immunomodulatory activity of L. gasseri JM1 and explore the underlying signaling pathways in vitro. The results showed that pretreatment with L. gasseri JM1 alleviated lipopolysaccharide-induced inflammatory response, as evidenced by downregulation of genes encoding proinflammatory cytokines [IL1B, IL6, IL8, and tumor necrosis factor-α (TNFA)] and upregulation of genes encoding anti-inflammatory cytokines [IL4, IL10, transforming growth factor-ß3 (TGFB3), and IFNG]. A high level of gene expression was noted for toll-like receptor 2 and NOD-like receptor 2. Meanwhile, transcriptomic sequencing obtained 84 differentially expressed genes. Kyoto Encyclopedia of Genes and Genomes analysis revealed the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway was activated by L. gasseri JM1 in Caco-2 cells. Inhibitor of PI3K/Akt played various roles in the release of cytokines, indicating that the pathway was involved in protecting the host against lipopolysaccharide stress. Moreover, whole-genome sequencing revealed fundamental genetic properties of L. gasseri JM1 and provided clues for probiotic characteristics. In summary, the strain could exert immunomodulatory effects via the toll-like receptor 2 and NOD2-mediated PI3K/Akt signaling pathway and be regarded as a potential probiotic.

A novel fluorometric aptasensor based on carbon nanocomposite for sensitive detection of Escherichia coli O157:H7 in milk.

Escherichia coli O157:H7 is an extremely serious foodborne pathogen accounting for a vast number of hospitalizations. In this system, a simple, rapid, and safe compound method was developed based on carbonyl iron powder (CIP) and multiwalled carbon nanotubes (MWCNT). Then, the CIP@MWCNT-based aptasensor was constructed by strong π-stacking between nanocomposite and aptamer, single-strand DNA, causing fluorescent quenching of the dye-labeled aptamer. The restoration of dye fluorescence could be achieved when aptamer came off the surface of the CIP@MWCNT nanocomposite due to the presence of target bacteria. To the best of our knowledge, this fabrication of magnetic carbon nanotubes without irritating and corrosive reagents is described for the first time. The sensing platform was also an improvement on the conventional formation of the aptasensor between carbon materials and DNA aptamer. The nanocomposite was verified by diverse characterization of zeta potential, Fourier-transform infrared spectroscopy, transmission electron microscopy, and energy dispersive x-ray analysis. The CIP@MWCNT-based aptasensor was an effective nanoplatform for quantitative detection of E. coli O157:H7, and was measured to have high specificity, good reproducibility, and strong stability. The aptasensor's capacity to quantify E. coli O157:H7 was as low as 7.15 × 103 cfu/mL in pure culture. The detection limit of E. coli O157:H7 was 3.15 × 102 cfu/mL in contaminated milk after 1 h of pre-incubation. Hence, the developed assay is a new possibility for effective synthesis of nanocomposites and sensitive tests of foodborne pathogens in the dairy industry.

Short communication: Complete genome sequence of Lactobacillus plantarum J26, a probiotic strain with immunomodulatory activity.

Lactobacillus plantarum J26, a significant probiotic isolated from Chinese traditional fermented dairy products, exerts a positive immunomodulatory effect by regulating the expression of immune-related genes. We investigated expression of the cytokines IL-1α, IL-1ß, IL-6, and tumor necrosis factor-α in the intestinal tract of mice stimulated by L. plantarum J26. In vivo, these cytokines were upregulated, peaked on d 5, and then decreased to the control level, indicating that L. plantarum J26 could induce expression of the genes encoding these proinflammatory cytokines. Teichoic acids produced by L. plantarum are recognized as key immunomodulatory molecules involved in the regulation of the host immune response. To better understand the genetic basis of this immunomodulatory mechanism, we sequenced and analyzed the whole genome of L. plantarum J26. The genome of L. plantarum J26 contains a circular chromosome and 4 circular plasmids. Lactobacillus plantarum J26 was predicted to synthesize ribitol-type backbones of wall teichoic acid. Furthermore, orthologous average nucleotide identity (OrthoANI) values showed that the genome was highly similar (>98.00%) to other L. plantarum strains, especially to L. plantarum ST-III and JDM1. The genomic data of L. plantarum J26 provide a genetic basis to further elucidate its mechanism of immunoregulation and will facilitate its application in the functional dairy food industry.

Transcriptomic responses of Caco-2 cells to Lactobacillus rhamnosus GG and Lactobacillus plantarum J26 against oxidative stress.

Oxidative stress is the basic reason for aging and age-related diseases. In this study, we investigated the protective effect of 2 strains of lactic acid bacteria (LAB), Lactobacillus rhamnosus GG and L. plantarum J26, against oxidative stress in Caco-2 cells, and gave an overview of the mechanisms of lactic acid bacteria antioxidant activity using digital gene expression profiling. The 2 LAB strains provided significant protection against hydrogen peroxide (H2O2)-induced reduction in superoxide dismutase activity and increase in glutathione peroxidase activity in Caco-2 cells. However, inactive bacteria had little effect on alleviating oxidation stress in Caco-2 cells. Eight genes related to oxidative stress-FOSB, TNF, PPP1R15A, NUAK2, ATF3, TNFAIP3, EGR2, and FBN2-were significantly upregulated in H2O2-induced Caco-2 cells compared with untreated Caco-2 cells. After incubation of the H2O2-induced Caco-2 cells with L. rhamnosus GG and L. plantarum J26, 5 genes (TNF, EGR2, NUAK2, FBN2, and TNFAIP3) and 2 genes (NUAK2 and FBN2) were downregulated, respectively. In addition, the Kyoto Encyclopedia of Genes and Genomes indicated that some signaling pathways associated with inflammation, immune response, and apoptosis, such as Janus kinase/signal transducers and activators of transcription (Jak-STAT), mitogen-activated protein kinase (MAPK), nuclear factor-κB, and tumor necrosis factor, were all negatively modulated by the 2 strains, especially L. rhamnosus GG. In this paper, we reveal the mechanism of LAB in relieving oxidative stress and provide a theoretical basis for the rapid screening and evaluation of new LAB resources.

Typing and evaluating heat resistance of Bacillus cereus sensu stricto isolated from the processing environment of powdered infant formula.

Bacillus cereus sensu lato is one of the most harmful bacterial groups affecting the quality and safety of powdered infant formula (PIF). In this study, samples were collected from the raw materials and processing environments of PIF. A total of 84 isolates were identified as Bacillus cereus sensu stricto (B. cereus s. s.) by 16S rRNA analysis, molecular typing technology, and physiological and biochemical tests. The 84 B. cereus s. s. strains were assigned to panC group II, group III, and group IV. Then, the 7 housekeeping genes glpF, gmk, ilvD, pta, pur, pycA, and tpi were selected for multilocus sequence typing. Results showed that the 84 isolates were clustered into 24 sequence types (ST), and 14 novel ST were detected. Among the 24 ST, ST999 (19/84, 22.62%) and ST1343 (13/84, 15.48%) predominated. The correlation between processing areas and ST showed that the processing environments of the production and packing areas were the most susceptible to contamination by B. cereus s. s. Spores of these ST showed different heat resistance phenotypes evaluated by the analysis of DT (time in minutes of spore decimal reduction at each temperature) and Z values (temperature increase required to reduce the DT value to one-tenth of the original). Spores from group III according to panC gene analysis were the most heat resistant. These findings will help us to better understand B. cereus s. s. contamination and control in PIF processing environments.

Diversity and evolution of Lactobacillus casei group isolated from fermented dairy products in Tibet.

Bacteria in Lactobacillus casei group, including Lactobacillus casei (L. casei), Lactobacillus paracasei (L. paracasei), and Lactobacillus rhamnosus (L. rhamnosus) are important lactic acid bacteria in the production of fermented dairy products and are faced with the controversial nomenclatural status due to their close phylogenetic similarity. To probe the evolution and phylogeny of L. casei group, 100 isolates of lactic acid bacteria originated from naturally fermented dairy products in Tibet of China were subjected to multilocus sequence typing (MLST). The MLST scheme, based on analysis of the housekeeping genes fusA, ileS, lepA, leuS, pyrG, recA and recG, revealed that all the isolates belonged to a group containing the L. paracasei reference strains and were clearly different from the strains of L. casei and L. rhamnosus. Although nucleotide diversity (π) was low for the seven genes (ranging from 0.00341 for fusA to 0.01307 for recG), high genetic diversity represented by 83 sequence types (STs) with a discriminatory index of 0.98 was detected. A network-like structure based on split decomposition analysis, and the high values of the relative effect of recombination and mutation in the diversification of the lineages (r/m = 4.76) and the relative frequency of occurrence of recombination and mutation (ρ/θ = 2.62) indicated that intra-species recombination occurred frequently and homologous recombination played a key role in generating genotypic diversity amongst L. paracasei strains in Tibet. The discovery of 51 new STs and the results of STRUCTURE analysis suggested that the L. casei group in Tibet had an individual and particular population structure in comparison to European isolates. Overall, this research might be the first report about genetic diversity and population structure of Lactobacillus populations isolated from naturally fermented dairy products in Tibet based on MLST scheme.