Adhesion and invasion of Listeria monocytogenes and interaction with Lactobacillus rhamnosus GG after habituation on fresh-cut pear

An Untargeted Metabolomic Analysis of Lacticaseibacillus (L.) rhamnosus, Lactobacillus (L.) acidophilus, Lactiplantibacillus (L.) plantarum and Limosilactobacillus (L.) reuteri Reveals an Upregulated Production of Inosine from L. rhamnosus

Lactic acid bacteria are considered an inexhaustible source of bioactive compounds; indeed, products from their metabolism are known to have immunomodulatory and anti-inflammatory activity. Recently, we demonstrated that Cell-Free Supernatants (CFS) obtained from Lactobacillus (L.) acidophilus, Lactiplantibacillus (L.) plantarum, Lacticaseibacillus (L.) rhamnosus, and Limosilactobacillus (L.) reuteri can impair Candida pathogenic potential in an in vitro model of epithelial vaginal infection. This effect could be ascribed to a direct effect of living lactic acid bacteria on Candida virulence and to the production of metabolites that are able to impair fungal virulence. In the present work, stemming from these data, we deepened our knowledge of CFS from these four lactic acid bacteria by performing a metabolomic analysis to better characterize their composition. By using an untargeted metabolomic approach, we detected consistent differences in the metabolites produced by these four different lactic acid bacteria. Interestingly, L. rhamnosus and L. acidophilus showed the most peculiar metabolic profiles. Specifically, after a hierarchical clustering analysis, L. rhamnosus and L. acidophilus showed specific areas of significantly overexpressed metabolites that strongly differed from the same areas in other lactic acid bacteria. From the overexpressed compounds in these areas, inosine from L. rhamnosus returned with the best identification profile. This molecule has been described as having antioxidant, anti-inflammatory, anti-infective, and neuroprotective properties. The biological significance of its overproduction by L. rhamnosus might be important in its probiotic and/or postbiotic activity.

Evaluation of Commercial Anti-Listerial Products for Improvement of Food Safety in Ready-to-Eat Meat and Dairy Products

In ready-to-eat products, such as cooked ham, fresh cheese, and fuet in which Listeria monocytogenes is a concern, the use of biopreservation techniques represents an additional hurdle to inhibit pathogen growth during storage. The objective of this study was to apply several biopreservation techniques in three different food matrices to reduce the growth of Listeria innocua, used as a surrogate of L. monocytogenes. Several lactic acid bacteria, the bacteriocin nisin, the bacteriophage PhageGuard Listex^TM P100, and the enzyme lysozyme were evaluated. Cooked ham treated with the bacteriophage PhageGuard Listex^TM at 0.5% or with the lactic acid bacteria SafePro^® B-SF-43 (25 g/100 kg) reduced L. innocua population to below the detection limit after 7 days of storage (4 °C plus modified atmosphere packaging). In fresh cheese, the application of PhageGuard Listex^TM at 0.2 and 0.5% reduced L. innocua counts by more than 3.4 logarithmic units after 6 days at 4 °C. In fuet, the 1.0% of PhageGuard Listex^TM reduced L. innocua population by 0.7 ± 0.2 logarithmic units in front of control with no significant differences to other evaluated biopreservative agents. The present results confirm that the application of biopreservation techniques was able to inhibit L. innocua in fuet, cooked ham, and fresh cheese, and suggest that the type of food matrix and its physicochemical characteristics influence the biopreservative efficacy.

Lactobacilli, a Weapon to Counteract Pathogens through the Inhibition of Their Virulence Factors

To date, several studies have reported an alarming increase in pathogen resistance to current antibiotic therapies and treatments. Therefore, the search for effective alternatives to counter their spread and the onset of infections is becoming increasingly important.

Effect of vacuum impregnation assisted probiotics fermentation suspension on shelf life quality of freshly cut lotus root

Probiotic fermentation suspension was used to extend the shelf life of freshly cut lotus root for the first time, which played a dual role of biological protection and quality maintenance. Fermentation suspension contained lactic acid bacteria (8-9 log CFU/mL) was prepared from juice of lotus root and used to immerse samples under atmospheric pressure and vacuum. Probiotic fermentation suspension inhibited microorganism and the activity of polyphenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonia lyase (PAL), which slowed down the physiological reaction and was beneficial to maintain the color and hardness of tissues. Lactic acid bacteria antagonized other microorganisms, and metabolic acid production played a continuous role in preservation during storage. The vacuum was helpful for the fermentation suspension to be fully impregnated into samples. The probiotic fermentation suspension had a significant inhibitory effect on E.coli O157:H7, and extended lotus root shelf life from 3 to 9 days.

Lactiplantibacillus plantarum subsp. plantarum and Fructooligosaccharides Combination Inhibits the Growth, Adhesion, Invasion, and Virulence of Listeria monocytogenes

Listeria monocytogenes is a foodborne pathogen responsible for many food outbreaks worldwide. This study aimed to investigate the single and combined effect of fructooligosaccharides (FOS) and Lactiplantibacillus plantarum subsp. plantarum CICC 6257 (L. plantarum) on the growth, adhesion, invasion, and virulence of gene expressions of Listeria monocytogenes 19112 serotype 4b (L. monocytogenes). Results showed that L. plantarum combined with 2% and 4% (w/v) FOS significantly (p < 0.05) inhibited the growth of L. monocytogenes (3-3.5 log10 CFU/mL reduction) at the incubation temperature of 10 °C and 25 °C. Under the same combination condition, the invasion rates of L. monocytogenes to Caco-2 and BeWo cells were reduced more than 90% compared to the result of the untreated group. After L. plantarum was combined with the 2% and 4% (w/v) FOS treatment, the gene expression of actin-based motility, sigma factor, internalin A, internalin B, positive regulatory factor A, and listeriolysin O significantly (p < 0.05) were reduced over 91%, 77%, 92%, 89%, 79%, and 79% compared to the result of the untreated group, respectively. The inhibition level of the L. plantarum and FOS combination against L. monocytogenes was higher than that of FOS or L. plantarum alone. Overall, these results indicated that the L. plantarum and FOS combination might be an effective formula against L. monocytogenes.

Transcriptomic Response of L. monocytogenes to Co-Culture with S. cerevisiae

The aim of the present study was to assess the transcriptomic response of L. monocytogenes during co-culture with three S. cerevisiae strains. For this purpose, BHI broth was inoculated with 7 log CFU·mL−1 L. monocytogenes serotype 4b strain LQC 15257, isolated from a strawberry sample and 4 log CFU·mL−1 S. cerevisiae strains Y32, Y34 and Y37, isolated from spontaneous olive fermentation. Sampling took place after 24 and 48 h incubation at 5 and 20 °C. RNA was extracted, stabilized and the transcription of virulence associated genes prfA, sigB, hly, plcA, plcB, inlA, inlB, inlC and inlJ, was assessed by RT-qPCR. Co-culture with the yeast strains mostly affected the transcription of sigB and inlJ, the upregulation of which during growth at 5 °C for 24 h, reached 10.13 and 9.76 log2(fold change), respectively. Similarly, the effect that incubation time had on the relative transcription of the genes under study was dependent on the co-cultivating yeast strain. On the other hand, the effect of the yeast strain was less pronounced when the relative transcription of the genes under study was assessed between 20 °C and 5 °C. In that case, incubation temperature seemed to have an important effect since, in the 79.2% of the samples analyzed, upregulation was evident, irrespective of yeast strain presence. These results highlight the complex trophic relationships that take place during co-existence between L. monocytogenes and S. cerevisiae.

Role of biological control agents and physical treatments in maintaining the quality of fresh and minimally-processed fruit and vegetables

Fruit and vegetables are an important part of human diets and provide multiple health benefits. However, due to the short shelf-life of fresh and minimally-processed fruit and vegetables, significant losses occur throughout the food distribution chain. Shelf-life extension requires preserving both the quality and safety of food products. The quality of fruit and vegetables, either fresh or fresh-cut, depends on many factors and can be determined by analytical or sensory evaluation methods. Among the various technologies used to maintain the quality and increase shelf-life of fresh and minimally-processed fruit and vegetables, biological control is a promising approach. Biological control refers to postharvest control of pathogens using microbial cultures. With respect to application of biological control for increasing the shelf-life of food, the term biopreservation is favored, although the approach is identical. The methods for screening and development of biocontrol agents differ greatly according to their intended application, but the efficacy of all current approaches following scale-up to commercial conditions is recognized as insufficient. The combination of biological and physical methods to maintain quality has the potential to overcome the limitations of current approaches. This review compares biocontrol and biopreservation approaches, alone and in combination with physical methods. The recent increase in the use of meta-omics approaches and other innovative technologies, has led to the emergence of new strategies to increase the shelf-life of fruit and vegetables, which are also discussed herein.

Evaluation of postharvest calcium treatment and biopreservation with Lactobacillus rhamnosus GG on the quality of fresh-cut 'Conference' pears

BACKGROUND

Biological preservation with probiotic bacteria has arisen as an alternative to control the growth of foodborne pathogens on food. The objective of this work was to evaluate the effect of postharvest calcium application and biopreservation with Lactobacillus rhamnosus GG on the quality and bioaccessibility of total phenolic content and antioxidant activity in fresh-cut pears.

RESULTS

The immersion of whole pears in a calcium chloride solution did not provide added value. Despite the increase in observed activity of PME and PPO enzymes in fresh-cut pears during storage, the browning index and firmness values were constant for all samples. The antioxidant properties, including antioxidant activity, total phenolic content and vitamin C content, were maintained during storage, but a significant decrease was observed after in vitro simulated digestion. Ca/LGG samples showed the lowest calcium content (1.75 ± 0.00 g kg^-1 ) after 9 d of storage at 4 °C. In general, the overall visual quality scores were higher in fresh-cut pears treated with L. rhamnosus GG than in non-treated pears, with the highest values in the NoCa/LGG (7.7 ± 0.2) samples after 9 d at 4 °C.

CONCLUSION

Fresh-cut pears with a postharvest treatment of calcium and immersed in a solution containing antioxidant agents and probiotic bacteria could be a suitable alternative to dairy products for maintaining the overall quality of fruit for up to 9 d of storage. © 2018 Society of Chemical Industry.