Evaluation of the effect of Lactobacillus sakei strain L115 on Listeria monocytogenes at different conditions of temperature by using predictive interaction models

Shelf life estimation of refrigerated vacuum packed beef accounting for uncertainty

This study estimates the shelf life of vacuum packed beef meat (three muscles: striploin (longissimus thoracis et lumborum, LTL), tenderloin (psoas major, PM) and outside chuck (trapezius thoracis, TT)) at refrigeration temperatures (0 °C-10 °C) based on modelling the growth of two relevant groups of spoilage microorganisms: lactic acid bacteria (LAB) and Enterobacteriaceae. The growth models were developed combining a two-step and a one-step approach. The primary modelling was used to identify the parameters affecting the growth kinetics, guiding the definition of secondary growth models. For LAB, the secondary model included the effect of temperature and initial pH on the specific growth rate. On the other hand, the model for Enterobacteriaceae incorporated the effect of temperature on the specific growth rate and the lag phase; as well as the effect of the initial pH on the specific growth rate, the lag phase and the initial microbial count. We did not observe any significant effect of the type of muscle on the growth kinetics. Once the equations were defined, the models were fitted to the complete dataset using a one-step approach. Model validation was carried out by cross-validation, mitigating the impact of an arbitrary division between training and validation sets. The models were used to estimate the shelf life of the product, based on the maximum admissible microbial concentration (7 log CFU/g for LAB, 5 log CFU/g for Enterobacteriaceae). Although LAB was the dominant microbiota, in several cases, both LAB and Enterobacteriaceae reached the critical concentration practically at the same time. Furthermore, in some scenarios, the end of shelf life would be determined by Enterobacteriaceae, pointing at the potential importance of non-dominant microorganisms for product spoilage. These results can aid in the implementation of effective control measures in the meat processing industry.

Characterization of bacteriocins produced by Lactobacillus species against adhesion and invasion of Listeria monocytogenes isolated from different samples

BACKGROUND

Listeria monocytogenes is an important difficult to control and eradicate foodborne pathogen due to its resistance properties to extreme conditions. Bacteriocins produced by lactic acid bacteria (LAB) can be considered as natural alternatives for safety and quality of foods, since these molecules offer antimicrobial activity against other bacteria.

METHODS

In this study, Lacticaseibacillus casei, Lactiplantibacillus plantarum, and L. monocytogenes isolates were first characterized by phenotypical tests and 16S rRNA gene using PCR. Then, six types of bacteriocins produced by Lactobacilli strains were identified using molecular tests. The ability of these strains to compete with L. monocytogenes for adhesion and invasion to HT-29 cells was evaluated through colony count and MTT assay. Finally, the level of bacteriocins expression was assessed using qRT-PCR.

RESULTS

L. monocytogenes strains were categorized from A1 to A8 based on the source of isolation. In the adhesion assay, L. casei + L. monocytogenes isolated from milk and Lpb plantarum + L. monocytogenes isolated from feces presented the maximum adherence values. Further, Lpb plantarum + L. monocytogenes isolated from blood invaded to HT-29 cell line at the highest level. Eventually, L. casei + Lpb plantarum + L. monocytogenes isolated from placenta revealed more expression levels in comparison with other groups.

CONCLUSION

These results suggest a practical approach to classifying bacteriocins into functional groups that could be used for identifying the best mixture of bacteriocins for usage against L. monocytogenes.

Lactobacillus plantarum Lp62 exerts probiotic effects against Gardnerella vaginalis ATCC 49154 in bacterial vaginosis

The severe side-effects elicited by conventional antibiotic therapy and the recurrence of Bacterial vaginosis-associated bacteria and bacterial resistance have led to the development of novel alternative therapies, among which genital probiotics are widely used. In this study, we aimed to evaluate the antimicrobial activities of Lactobacillus plantarum Lp62 and its supernatant against Gardnerella vaginalis, using both in vitro and in vivo approaches. In vitro assays were used to evaluate the viability of the strain and the antimicrobial activities of the supernatant in different pH ranges. An in vivo assay was performed on female BALB/c mice, wherein the animals were divided into eight groups: four control groups and four treated groups (for curative and preventive therapies). After infecting and treating the mice, the animals were killed to quantify the bacterial load using qPCR, evaluate leucocyte cellular response, determine vaginal cytokine levels and perform cytokine tissue gene expression. Our analyses revealed significant activity of the strain and its supernatant against G. vaginalis. Preliminary in vitro tests showed that the strain grew with equal efficiency in different pH ranges. Meanwhile, the presence of halo and inhibition of pathogen growth established the significant activity of the supernatant against G. vaginalis. We observed that both micro-organisms are resident bacteria of mouse microbiota and that the lactobacilli population growth was affected by G. vaginalis and vice versa. We also observed that the treated groups, with their low bacterial load, absence of leucocyte recruitment, reduced cytokine levels in the vaginal lavage and normalized cytokine gene expression, successfully controlled the infection.

Optimization of the Effects of Different Temperatures and Compositions of Filmogenic Solution on Lactobacillus Salivarius Using Predictive Mathematical Models

It is well known that intake of probiotic brings health benefits. Lactic bacteria with probiotic potential have aroused the interest of the industry in developing food products that incorporate such benefits. However, incorporating probiotic bacteria into food is a challenge for the industry, given the sensitivity of probiotic cultures to process conditions. Therefore, the objective of this study is to evaluate gelatin- and inulin-based filmogenic solutions as a potential vehicle for incorporating probiotics into food products and to model the fermentation kinetics. L. salivarius (Lactobacillus salivarius) growth in filmogenic solutions was analyzed under the influence of a variety gelatin concentrations (1.0–3.0%) and inulin concentrations (4.0–6.0%) and fermented under the effect of different temperatures (25–45 °C). A full 2³ factorial plan with three replicates at the central point was used to optimize the process. The impacts of process conditions on cell development are fundamental to optimize the process and make it applicable by the industry. The present study showed that the optimal conditions for the development of probiotic cells in filmogenic solutions are a combination of 1.0% gelatin with 4.0% inulin and fermentation temperature of 45 °C. It was observed that the maximum cell growth occurred in an estimated time of about 4 h of fermentation. L. salivarius cell production and substrate consumption during the fermentation of the filmogenic solution were well simulated by a model proposed in this article, with coefficients of determination of 0.981 (cell growth) and 0.991 (substrate consumption).