Quantitative microbiological risk assessment for the occurrence of listeriosis in Brazil due to the consumption of milk processed by pasteurization or thermosonication

This study aimed to estimate the risk of listeriosis from the consumption of pasteurized milk in Brazil, comparing conventional treatment with the technology of thermosonication. The Quantitative Microbiological Risk Assessment (QMRA) model was developed, covering the entire milk production chain, from milking to the moment of consumption. In general, higher risks were observed in association with higher initial concentrations of the pathogen and the vulnerable population. The highest risk predicted (3.67 × 10-5) was related to the scenario considering the initial concentration range of L. monocytogenes between 4 and 6 log CFU/mL, with conventional treatment and considering the vulnerable population, resulting in one case of listeriosis every 27,248 servings. When considering thermosonication treatment, lower risks have been predicted. The scenario analysis indicated that the steps related to storage conditions in retail and at the consumer's home (post-processing steps) are the most influential in the associated risk, in all scenarios. The predictive parameters of inactivation related to the applied treatment also have a considerable influence on the risk. The results point to the influence of the stages of the dairy production chain and the thermosonication treatment applied in the food safety of milk, subsidizing information for industrial application and for regulatory agencies.

Comparative genomics reveals key molecular targets for mutant Pediococcus pentosaceus C23221 producing pediocin

Listeria monocytogenes is a common microorganism that causes food spoilage. Pediocins are some biologically active peptides or proteins encoded by ribosomes, which have a strong antimicrobial activity against L. monocytogenes. In this study, the antimicrobial activity of previously isolated P. pentosaceus C-2-1 was enhanced by ultraviolet (UV) mutagenesis. A positive mutant strain P. pentosaceus C23221 was obtained after 8 rounds of UV irradiation with increased antimicrobial activity of 1448 IU/mL, which was 8.47 folds higher than that of wild-type C-2-1. The genome of strain C23221 and wild-type C-2-1 was compared with identify the key genes for higher activity. The genome of the mutant strain C23221 consists of a chromosome of 1,742,268 bp, with 2052 protein-coding genes, 4 rRNA operons, and 47 tRNA genes, which is 79,769 bp less than the original strain. Compared with strain C-2-1, a total of 19 deduced proteins involved in 47 genes are unique to C23221 analyzed by GO database; the specific ped gene related to bacteriocin biosynthesis were detected using antiSMASH in mutant C23221, indicating mutant C23221 produced a new bacteriocin under mutagenesis conditions. This study provides genetic basis for further constituting a rational strategy to genetically engineer wild-type C-2-1 into an overproducer.

Current approaches on the roles of lactic acid bacteria in crop silage

Lactic acid bacteria (LAB) play pivotal roles in the preservation and fermentation of forage crops in spontaneous or inoculated silages. Highlights of silage LAB over the past decades include the discovery of the roles of LAB in silage bacterial communities and metabolism and the exploration of functional properties. The present article reviews published literature on the effects of LAB on the succession, structure, and functions of silage microbial communities involved in fermentation. Furthermore, the utility of functional LAB in silage preparation including feruloyl esterase-producing LAB, antimicrobial LAB, lactic acid bacteria with high antioxidant potential, pesticide-degrading LAB, lactic acid bacteria producing 1,2-propanediol, and low-temperature-tolerant LAB have been described. Compared with conventional LAB, functional LAB produce different effects; specifically, they positively affect animal performance, health, and product quality, among others. In addition, the metabolic profiles of ensiled forages show that plentiful probiotic metabolites with but not limited to antimicrobial, antioxidant, aromatic, and anti-inflammatory properties are observed in silage. Collectively, the current knowledge on the roles of LAB in crop silage indicates there are great opportunities to develop silage not only as a fermented feed but also as a vehicle of delivery of probiotic substances for animal health and welfare in the future.

Effects of Bacteriocin-Producing Lactiplantibacillus Plantarum on Fermentation, Dynamics of Bacterial Community, and Their Functional Shifts of Alfalfa Silage with Different Dry Matters

This study investigated the effects of two bacteriocin-producing Lactiplantibacillus plantarum strains on fermentation, bacterial communities, and their functions of alfalfa silage with two dry matter (DM) contents of 355 (moderate DM) and 428 (high DM) g/kg fresh weight. Before ensiling, alfalfa was treated with (1) distilled water (control), (2) the commercial strain L. plantarum MTD/1, (3) bacteriocin-producing L. plantarum ATCC14917, and (4) bacteriocin-producing L. plantarum LP1-4, and ensiled for 3 d, 7 d, 14 d, 60 d, and 90 d, respectively. Application of ATCC14917 promoted lactic acid production in the moderate DM silage at the early fermentation stage (3 d). Silages treated with ATCC14917 and LP1-4 showed lower DM losses and non-protein nitrogen concentrations versus the control or MDT/1-treated silage (p < 0.05). During fermentation, a high proportion of Weissella cibaria was observed in the silages with high DM content from 3 to 60 d of ensiling, and the functions of carbohydrate and amino acid metabolisms of silage bacterial community were decreased by ATCC14917 before 60 d of ensiling. In addition, ATCC14917 also inhibited the growth of Aerococcus and Enterobacter in silage. Therefore, the bacteriocin-producing L. plantarum ATCC14917 has a great potential to improve alfalfa silage quality, nutritive value, and safety as well.

Challenges and opportunities for the production of lactic acid bacteria inoculants aimed for ensiling processes

The use of bacterial inoculants for ensiling based on lactic acid bacteria (LAB) to obtain conserved forages has become an alternative for the improvement of milk and meat productivity in cattle, specifically by optimizing the nutritional and microbial quality of animal feed. LAB inoculant production involves microbial and technological aspects such as biomass obtention, the use of cocultures, the inclusion of probiotics, the production of antimicrobial peptides, operational methods used in bioreactors, and the formulation of the end product to be commercialized to farmers. This review explores the technical aspects of the manufacture of bacterial inoculants, from the main features desired in LAB for ensiling purposes to the alternatives of the bioprocess involved.

Wildlife symbiotic bacteria are indicators of the health status of the host and its ecosystem

Lactic acid bacteria (LAB) are gut symbionts that can be used as a model to understand the host-microbiota crosstalk under unpredictable environmental conditions such as wildlife ecosystems. The aim of this study was to determine whether viable LAB can be informative of the health status of wild boar populations. We monitored the genotype and phenotype of LAB based on markers that included safety and phylogenetic origin, antibacterial activity and immunomodulatory properties. A LAB profile dominated by lactobacilli appears to stimulate protective immune responses and relates to strains widely used as probiotics, resulting in a potentially healthy wildlife population whereas microbiota overpopulated by enterococci was observed in a hostile environment. These enterococci were closely related to pathogenic strains that have developed mechanisms to evade innate immune system, posing a potential risk for the host health. Furthermore, our LAB isolates displayed antibacterial properties in a species-dependent manner. Nearly all of them were able to inhibit bacterial pathogens, raising the possibility of using them as a la carte antibiotic alternative in the unexplored field of wildlife disease mitigation. Our study highlights that microbiological characterization of LAB is a useful indicator of wildlife health status and the ecological origin from which they derive. Significance Statement The wildlife symbiotic microbiota is an important component to the greater for greater diversity and functionality of their bacterial populations, influencing the host health and adaptability to its ecosystem. Although many microbes are partly responsible for the development of multiple physiological processes, only certain bacterial groups such as lactic acid bacteria (LAB) have the capacity to overpopulate the gut, promoting health (or disease) when specific genetic and environmental conditions are present. LAB have been exploited in many ways due to their probiotic properties, in particular lactobacilli, however their relationship with wildlife gut-associated microbiota hosts remains to be elucidated. On the other hand, it is unclear whether LAB such as enterococci, which have been associated with detrimental health effects, could lead to disease. These important questions have not been properly addressed in the field of wildlife, and therefore, should be clearly attained.

Probiotic Characterization and Population Diversity Analysis of Gut-Associated Pediococcus acidilactici for Its Potential Use in the Dairy Industry

In recent years, gut-tailored probiotics have been proven to be beneficial for host health. Probiotic strains such as lactic acid bacteria (LAB) are known to exhibit antimicrobial activity, acting as natural substitutes for the regulation of foodborne pathogens. In the present study, a complete analysis, isolation, biochemical characterization, and molecular identification of Pediococcus acidilactici (NMCC-11) from Nili Ravi water buffalo (Bubalis bubalis) gut was carried out. NMCC-11 showed the best enzymatic potential, antimicrobial activity against known pathogenic strains, and survivability at a wide pH range (pH 4–pH 6) out of all isolates. The isolates were screened for their antimicrobial activity against the five most infectious microbes such as Escherichia coli (ATCC 8739), Pseudomonas aeruginosa (ATCC9027), Staphylococcus aureus (ATCC6538), Listeria monocytogenes (ATCC13932), and Bacillus cereus (ATCC 11778) using the agar-well diffusion method. Moreover, after NMCC-11 isolation, a comparative diversity analysis against a variety of other randomly selected strains from around the world was carried out using R software. This study showed relatively low genetic diversity, which also contributed to the claim of the stability of this probiotic strain and its potential use as a starter culture and feed probiotic in the dairy industry. However, further studies are certainly warranted to determine its optimal dosage, time frame, and intake frequency.

Effects of Class IIa Bacteriocin-Producing Lactobacillus Species on Fermentation Quality and Aerobic Stability of Alfalfa Silage

Simple Summary

Bacteriocins produced by lactic acid bacteria are considered good alternatives for feed antibiotics because of inhibiting spoilage microorganisms in silage and non-drug resistance in animals. Owing to the narrow antibacterial spectrum, class I bacteriocin-producing lactic acid bacteria are considered to have limitations as silage inoculants. The research was conducted to evaluate the effects of two class IIa bacteriocin-producing Lactobacillus on silage fermentation, microbial population, chemical composition, and aerobic stability. The strains results showed that class IIa bacteriocin-producing lactic acid bacteria could improve silage fermentation quality, reduce counts of molds and yeasts, and improve aerobic stability to a greater extent than inoculation with Lactobacillus plantarum MTD/1, a proven, widely used inoculant, which does not produce bacteriocin. The findings of this research are of great value for current understandings and onwards to conduct further research and for possible practical implementation of class IIa bacteriocin-producing lactic acid bacteria as silage inoculants.

Abstract

The effects of two strains of class IIa bacteriocin-producing lactic acid bacteria, Lactobacillus delbrueckii F17 and Lactobacillus plantarum (BNCC 336943), or a non-bacteriocin Lactobacillus plantarum MTD/1 (NCIMB 40027), on fermentation quality, microbial counts, and aerobic stability of alfalfa silage were investigated. Alfalfa was harvested at the initial flowering stage, wilted to a dry matter concentration of approximately 32%, and chopped to 1 to 2 cm length. Chopped samples were treated with nothing (control, CON), Lactobacillus delbrueckii F17 (F17), Lactobacillus plantarum (BNCC 336943) (LPB), or Lactobacillus plantarum MTD/1 (NCIMB 40027) (LPN), each at an application rate of 1 × 10⁶ colony-forming units/g of fresh weight. Each treatment was ensiled in quadruplicate in vacuum-sealed polyethylene bags packed with 500 g of fresh alfalfa per bag and ensiled at ambient temperature (25 ± 2 °C) for 3, 7, 14, 30, and 60 days. The samples were then subjected to an aerobic stability test after 60 days of ensiling. Compared with the CON silage, the inoculants reduced the pH after 14 days of ensiling. After 60 days, pH was lowest in the LPB-treated silage, followed by the F17 and LPN-treated silages. Inoculation of F17 increased concentrations of lactic acid in silages fermented for 7, 14, 30, and 60 days relative to other treatments, except for the LPN-treated silages ensiled for 30 and 60 days, in which the lactic acid concentrations were similar to that of F17 silage. Application of F17 and LPB decreased the number of yeast and mold relative to CON and LPN-treated silages. Compared with the CON silage, inoculant-treated silages had greater aerobic stability, water-soluble carbohydrate, and crude protein concentrations, and lower neutral detergent fiber, amino acid nitrogen, and ammonia nitrogen concentrations. The LPB-treated silage had the greatest aerobic stability followed by the F17-treated silage. Both class IIa bacteriocin producing inoculants improved alfalfa silage fermentation quality, reduced the growth of yeasts and molds, and improved the aerobic stability of the ensiled forage to a greater extent than the proven LPN inoculant. However, higher crude protein concentration and lower ammonia nitrogen concentration were observed in LPN-treated silage relative to other treatments.

Antimicrobial effect of spore-forming probiotics Bacillus laterosporus and Bacillus megaterium against Listeria monocytogenes

There are several reports on the detection of Listeria monocytogenes in Iran, which has been identified as a major public health problem. In addition, due to drug resistance and strong biofilm formation of this pathogen, new approaches such as using probiotics are needed to combat this bacterium. The aim of this study was to investigate the effect of spore-forming probiotics on the expression of virulence genes hly, plc, inlA, and invasion of L. monocytogenes. Spore-forming probiotics were co-cultured with L. monocytogenes at different time points and following cell count, the expression level of virulence genes of L. monocytogenes was assessed by real-time PCR. To investigate the effect of the isolated strains on the invasiveness of L. monocytogenes at different time points, HT-29 cell line was used. Sporulated probiotics reduced the growth of L. monocytogenes in broth medium at different time periods. The number of L. monocytogenes co-cultured with Bacillus laterosporus decreased by 1, 3, 3, and 6 log at 2, 4, 8 and 24 h after treatment, respectively. In addition, the expression of virulence genes was decreased at different time points and the expression of hly and plcA genes was more affected. The invasion rate of L. monocytogenes on HT-29 cells was decreased by 1 to 6 log at different time points. Both probiotic strains inhibited bacterial growth at different time points; however, more sensitive methods should be established for an accurate assessment.

Antibacterial and antifungal activity of crude and freeze-dried bacteriocin-like inhibitory substance produced by Pediococcus pentosaceus

Pediococcus pentosaceus LBM 18 has shown potential as producer of an antibacterial and antifungal bacteriocin-like inhibitory substance (BLIS). BLIS inhibited the growth of spoilage bacteria belonging to Lactobacillus, Enterococcus and Listeria genera with higher activity than Nisaplin used as control. It gave rise to inhibition halos with diameters from 9.70 to 20.00 mm, with Lactobacillus sakei being the most sensitive strain (13.50-20.00 mm). It also effectively suppressed the growth of fungi isolated from corn grain silage for up to 25 days and impaired morphology of colonies by likely affecting fungal membranes. These results point out that P. pentosaceus BLIS may be used as a new promising alternative to conventional antibacterial and antifungal substances, with potential applications in agriculture and food industry as a natural bio-controlling agent. Moreover, cytotoxicity and cell death induction tests demonstrated cytotoxicity and toxicity of BLIS to human colon adenocarcinoma Caco-2cells but not to peripheral blood mononuclear cells, with suggests possible applications of BLIS also in medical-pharmaceutical applications.