Complementary Antibacterial Effects of Bacteriocins and Organic Acids as Revealed by Comparative Analysis of Carnobacterium spp. from Meat

Carnobacterium maltaromaticum as bioprotective culture against spoilage bacteria in ground meat and cooked ham

This study assessed the bioprotective effect of Carnobacterium maltaromaticum (CM) against Pseudomonas fluorescens (PF) and Brochothrix thermosphacta (BT) in ground beef and sliced cooked ham stored in high- and low-oxygen-modified atmospheres (66/4/30% O2/N2/CO2 and 70/30% N2/CO2, respectively). Both meat products were inoculated with CM, PF, and BT individually or in combination and stored for 7 days (3 days at 4 °C + 4 days at 8 °C) for ground beef and 28 days (10 days at 4 °C + 18 days at 8 °C) for sliced cooked ham. Each food matrix was assigned to 6 treatments: NC (no bacterial inoculation, representing the indigenous bacteria of meat), CM, BT, PF, CM + BT, and CM + PF. Bacterial growth, pH, instrumental color, and headspace gas composition were assessed during storage. CM counts remained stable from inoculation and throughout the shelf-life. CM reduced the population of inoculated and indigenous spoilage bacteria, including BT, PF, and enterobacteria, and showed a negligible impact on the physicochemical quality parameters of the products. Furthermore, upon simulating the shelf-life of ground beef and cooked ham, a remarkable extension could be observed with CM. Therefore, CM could be exploited as a biopreservative in meat products to enhance quality and shelf-life.

Biorefinery of brewery spent grain to obtain bioproducts with high value-added in the market

The brewery industry is under economic and environmental pressure to minimize residual management costs, particularly brewery spent grain (BSG), which accounts for 80-85% (w/w) of the total by-products generated. BSG is a lignocellulosic material primarily composed of carbohydrates, proteins and lipids. Developing a biorefinery model for conversion of BSG into value-added products is a plausible idea. Previous work optimized the pretreatment of BSG with the ionic liquid [N1112OH][Gly] and further release of fermentable sugar-containing solutions by enzymatic hydrolysis, using an enzymatic cocktail obtained by solid-state fermentation of BSG with Aspergillus brasiliensis CECT 2700 and Trichoderma reesei CECT 2414. The current work ends the biorefinery process, studying the fermentation of these culture media with two LAB strains, Lactobacillus pentosus CECT 4023 and Lactobacillus plantarum CECT 221, from which the production of organic acids, bacteriocins, and microbial biosurfactants (mBS) was obtained. In addition to the bacteriocin activity observed, a mass balance of the whole biorefinery process quantified the production of 106.4 g lactic acid and 6.76 g mBS with L. plantarum and 116.1 g lactic acid and 4.65 g mBS with L. pentosus from 1 kg of dry BSG. Thus, BSG shows a great potential for waste valorization, playing a major role in the implementation of biomass biorefineries in circular bioeconomy.

Multiple genome sequences of lactic acid bacteria, Carnobacterium divergens and Carnobacterium maltaromaticum strains, isolated from vacuum-packaged lamb meat

Here, we report the whole-genome sequences of 11 Carnobacterium divergens and 2 Carnobacterium maltaromaticum bacteria isolated from vacuum-packed chill-stored lamb meat in New Zealand. Examination of these lactic acid bacteria (LAB) genomes will improve our knowledge of their potential antimicrobial activities and spoilage mechanisms of importance to the meat industry.

Potential Impact of Combined Inhibition by Bacteriocins and Chemical Substances of Foodborne Pathogenic and Spoilage Bacteria: A Review

In recent years, food safety caused by foodborne pathogens and spoilage bacteria has become a major public health problem worldwide. Bacteriocins are a kind of antibacterial peptide synthesized by microbial ribosomes, and are widely used as food preservatives. However, when used individually bacteriocins may have limitations such as high cost of isolation and purification, narrow inhibitory spectrum, easy degradation by enzymes, and vulnerability to complex food environments. Numerous studies have demonstrated that co-treatment with bacteriocins and a variety of chemical substances can have synergistic antibacterial effects on spoilage microorganisms and foodborne pathogens, effectively prolonging the shelf life of food and ensuring food safety. Therefore, this paper systematically summarizes the synergistic bacteriostatic strategies of bacteriocins in combination with chemical substances such as essential oils, plant extracts, and organic acids. The impacts of bacteriocins when used individually and in combination with other chemical substances on different food substrates are clarified, and bacteriocin-chemical substance compositions that enhance antibacterial effectiveness and reduce the potential negative effects of chemical preservatives are highlighted and discussed. Combined treatments involving bacteriocins and different kinds of chemical substances are expected to be a promising new antibacterial method and to become widely used in both the food industry and biological medicine.

Characterization of Bacteriophage cd2, a Siphophage Infecting Carnobacterium divergens and a Representative Species of a New Genus of Phage

Carnobacterium divergens is frequently isolated from natural environments and is a predominant species found in refrigerated foods, particularly meat, seafood, and dairy. While there is substantial interest in using C. divergens as biopreservatives and/or probiotics, some strains are known to be fish pathogens, and the uncontrolled growth of C. divergens has been associated with food spoilage. Bacteriophages offer a selective approach to identify and control the growth of bacteria; however, to date, few phages targeting C. divergens have been reported. In this study, we characterize bacteriophage cd2, which we recently isolated from minced beef. A detailed host range study reveals that phage cd2 infects certain phylogenetic groups of C. divergens. This phage has a latent period of 60 min and a burst size of ~28 PFU/infected cell. The phage was found to be acid and heat sensitive, with a complete loss of phage activity when stored at pH 2 or heated to 60°C. Electron microscopy shows that phage cd2 is a siphophage, and while it shares the B3 morphotype with a unique cluster of Listeria and Enterococcus phages, a comparison of genomes reveals that phage cd2 comprises a new genus of phage, which we have termed as Carnodivirus. IMPORTANCE Currently, very little is known about phages that infect carnobacteria, an important genus of lactic acid bacteria with both beneficial and detrimental effects in the food and aquaculture industries. This report provides a detailed characterization of phage cd2, a novel siphophage that targets Carnobacterium divergens, and sets the groundwork for understanding the biology of these phages and their potential use in the detection and biocontrol of C. divergens isolates.

Bacteriocin-Based Synergetic Consortia: a Promising Strategy to Enhance Antimicrobial Activity and Broaden the Spectrum of Inhibition

Bacteria-derived natural antimicrobial compounds such as bacteriocins, reruterin, and organic acids have recently received substantial attention as food preservatives or therapeutic alternatives in human or animal sectors. This study aimed to evaluate the antimicrobial activity of different bacteria-derived antimicrobials, alone or in combination, against a large panel of Gram-negative and Gram-positive bacteria. Bacteriocins, including microcin J25, pediocin PA-1, nisin Z, and reuterin, were investigated alone or in combination with lactic acid and citric acid, using a checkerboard assay. Concentrations were selected based on predetermined MICs against Salmonella enterica subsp. enterica serovar Newport ATCC 6962 and Listeria ivanovii HPB28 as Gram-negative and Gram-positive indicator strains, respectively. The results demonstrated that the combination of microcin J25 + citric acid + lactic acid; microcin J25 + reuterin + citric acid; and microcin J25 + reuterin + lactic acid tested against S. Newport ATCC 6962 showed synergistic effects (FIC index = 0.5). Moreover, a combination of pediocin PA-1 + citric acid + lactic acid; and reuterin + citric acid + lactic acid against L. ivanovii HPB28 showed a partially synergistic interactions (FIC index = 0.75). Nisin Z exerted a partially synergistic effect in combination with acids (FIC index = 0.625 -0.75), whereas when it was combined with reuterin or pediocin PA-1, it showed additive effects (FIC index = 1) against L. ivanovii HPB28. The inhibitory activity of synergetic consortia were tested against a large panel of Gram-positive and Gram-negative bacteria. According to our results, combining different antimicrobials with different mechanisms of action led to higher potency and a broad spectrum of inhibition, including multidrug-resistance pathogens.

IMPORTANCE Reuterin and bacteriocins, including microcin J25, pediocin PA-1, nisin were produced and purified with >90% purity. Using the broth-based checkerboard assay the interaction between these compounds (synergetic, additive, or antagonistic) was assessed. By combining different natural antimicrobials with different modes of action and structure (reuteirn, microcin J25, pediocin PA-1, and organic acids), we successfully developed five different synergetic consortia with improved antimicrobial activity and a broad spectrum of inhibition. These consortia were shown to be effective against a large panel of pathogenic and spoilage microorganisms as well as clinically important multidrug-resistance bacteria. Moreover, because the lower concentrations of bacteriocins and reuterin are used in the synergetic consortia, there is a limited risk of toxicity and resistance development for these compounds.

Novel pathways in bacteriocin synthesis by lactic acid bacteria with special reference to ethnic fermented foods

Ethnic fermented foods are known for their unique aroma, flavour, taste, texture and other sensory properties preferred by every ethnic community in this world culturally as parts of their eatables. Some beneficial microorganisms associated with fermented foods have several functional properties and health-promoting benefits. Bacteriocins are the secondary metabolites produced by the microorganisms mostly lactic acid bacteria present in the fermented foods which can act as lantibiotics against the pathogen bacteria. Several studies have been conducted regarding the isolation and characterization of potent strains as well as their association with different types of bacteriocins. Collective information regarding the gene organizations responsible for the potent effect of bacteriocins as lantibiotics, mode of action on pathogen bacterial cells is not yet available. This review focuses on the gene organizations, pathways include for bacteriocin and their mode of action for various classes of bacteriocins produced by lactic acid bacteria in some ethnic fermented foods.

Genome Sequences of Bacteriophages cd2, cd3, and cd4, which Specifically Target Carnobacterium divergens

Carnobacteria have been implicated in food spoilage, but also in protection against pathogenic bacteria. We report the isolation and complete genome sequences of three bacteriophages (phages cd2, cd3, and cd4) that specifically target Carnobacterium divergens. The genome sizes are approximately 57 kbp and have limited homology to known enterococcal and streptococcal phages.

Dynamic Modeling of Carnobacterium maltaromaticum CNCM I-3298 Growth and Metabolite Production and Model-Based Process Optimization

Carnobacterium maltaromaticum is a species of lactic acid bacteria found in dairy, meat, and fish, with technological properties useful in food biopreservation and flavor development. In more recent years, it has also proven to be a key element of biological time–temperature integrators for tracking temperature variations experienced by perishable foods along the cold-chain. A dynamic model for the growth of C. maltaromaticum CNCM I-3298 and production of four metabolites (formic acid, acetic acid, lactic acid, and ethanol) from trehalose in batch culture was developed using the reaction scheme formalism. The dependence of the specific growth and production rates as well as the product inhibition parameters on the operating conditions were described by the response surface method. The parameters of the model were calibrated from eight experiments, covering a broad spectrum of culture conditions (temperatures between 20 and 37 °C; pH between 6.0 and 9.5). The model was validated against another set of eight independent experiments performed under different conditions selected in the same range. The model correctly predicted the growth kinetics of C. maltaromaticum CNCM I-3298 as well as the dynamics of the carbon source conversion, with a mean relative error of 10% for biomass and 14% for trehalose and the metabolites. The paper illustrates that the proposed model is a valuable tool for optimizing the culture of C. maltaromaticum CNCM I-3298 by determining operating conditions that favor the production of biomass or selected metabolites. Model-based optimization may thus reduce the number of experiments and substantially speed up the process development, with potential applications in food technology for producing starters and improving the yield and productivity of the fermentation of sugars into metabolites of industrial interest.

The forgotten role of food cultures

Fermentation is one of if not the oldest food processing technique, yet it is still an emerging field when it comes to its numerous mechanisms of action and potential applications. The effect of microbial activity on the taste, bioavailability and preservation of the nutrients and the different food matrices has been deciphered by the insights of molecular microbiology. Among those roles of fermentation in the food chain, biopreservation remains the one most debated. Presumably because it has been underestimated for quite a while, and only considered - based on a food safety and technological approach - from the toxicological and chemical perspective. Biopreservation is not considered as a traditional use, where it has been by design - but forgotten - as the initial goal of fermentation. The 'modern' use of biopreservation is also slightly different from the traditional use, due mainly to changes in cooling of food and other ways of preservation, Extending shelf life is considered to be one of the properties of food additives, classifying - from our perspective - biopreservation wrongly and forgetting the role of fermentation and food cultures. The present review will summarize the current approaches of fermentation as a way to preserve and protect the food, considering the different way in which food cultures and this application could help tackle food waste as an additional control measure to ensure the safety of the food.

Genomic analysis of Shiga toxin-producing Escherichia coli O157:H7 from cattle and pork-production related environments

Three E. coli O157:H7 outbreaks have been attributed to contaminated pork in Alberta, Canada, recently. This study investigates the phylogenetic relatedness of E. coli O157:H7 from pigs, cattle, and pork-production environments for source attribution. Limited strain diversity was observed using five conventional subtyping methods, with most or all strains being in one subgroup. Whole-genome single nucleotide polymorphism analysis confirmed the recent ancestry of the isolates from all three sources. Most environmental isolates clustered closer with pig isolates than cattle isolates. Also, a direct link was observed between 2018-outbreak environmental isolates and isolates collected from a pig farm in 2018. The majority of pig isolates harbor only one Shiga toxin gene, stx_2a, while 70% (35/50) of the cattle isolates have both stx_1a and stx_2a. The results show some E. coli O157:H7 strains could establish persistence on pig farms and as such, pigs can be a significant source of the organism.

Metataxonomic profiling of bacterial communities and their predictive functional profiles in traditionally preserved meat products of Sikkim state in India

Traditionally preserved meat products are common food items in Sikkim state of India. We studied the high-throughput sequencing of four traditionally preserved meat products viz. beef kargyong, pork kargyong, yak satchu and khyopeh to profile the bacterial communities and also inferred their predictive functional profiles. Overall abundant OTUs in samples showed that Firmicutes was the abundant phylum followed by Proteobacteria and Bacteroidetes. Abundant species detected in each product were Psychrobacter pulmonis in beef kargyong, Lactobacillus sakei in pork kargyong, Bdellovibrio bacteriovorus and Ignatzschinera sp. in yak satchu and Lactobacillus sakei and Enterococcus sp. in khyopeh. Several genera unique to each product, based on analysis of shared OTUs contents, were observed among the samples except in khyopeh. Goods coverage recorded to 1.0 was observed, which reflected the maximum bacterial diversity in the samples. Alpha diversity metrics showed a maximum bacterial diversity in khyopeh and lowest in pork kargyong Community dissimilarities in the products were observed by PCoA plot. A total of 133 KEGG predictive functional pathways was observed in beef kargyong, 131 in pork kargyong, 125 in yak satchu and 101 in khyopeh. Metagenome contribution of the OTUs was computed using PICTRUSt2 and visualized by BURRITO software to predict the metabolic pathways. Several predictive functional profiles were contributed by abundant OTUs represented by Enterococcus, Acinetobacter, Agrobacterium, Bdellovibrio, Chryseobacterium, Lactococcus, Leuconostoc, Psychrobacter, and Staphylococcus.

Lactic Acid Bacteria Adjunct Cultures Exert a Mitigation Effect against Spoilage Microbiota in Fresh Cheese

Lactic acid bacteria (LAB) have a strong mitigation potential as adjunct cultures to inhibit undesirable bacteria in fermented foods. In fresh cheese with low salt concentration, spoilage and pathogenic bacteria can affect the shelf life with smear on the surface and packaging blowing. In this work, we studied the spoilage microbiota of an Italian fresh cheese to find tailor-made protective cultures for its shelf life improvement. On 14-tested LAB, three of them, namely Lacticaseibacillus rhamnosus LRH05, Latilactobacillus sakei LSK04, and Carnobacterium maltaromaticum CNB06 were the most effective in inhibiting Gram-negative bacteria. These cultures were assessed by the cultivation-dependent and DNA metabarcoding approach using in vitro experiments and industrial trials. Soft cheese with and without adjunct cultures were prepared and stored at 8 and 14 °C until the end of the shelf life in modified atmosphere packaging. Data demonstrated that the use of adjunct cultures reduce and/or modulate the growth of spoilage microbiota at both temperatures. Particularly, during industrial experiments, C. maltaromaticum CNB06 and Lcb. rhamnosus RH05 lowered psychrotrophic bacteria of almost 3 Log CFU/g in a 5-week stored cheese. On the contrary, Llb. sakei LSK04 was able to colonize the cheese but it was not a good candidate for its inhibition capacity. The combined approach applied in this work allowed to evaluate the protective potential of LAB strains against Gram-negative communities.

Synergistic inhibition mechanism of pediocin PA-1 and L-lactic acid against Aeromonas hydrophila

Pediocin PA-1 (PA-1) is a membrane-targeting bacteriocin from lactic acid bacteria, which shows antimicrobial activity against a wide range of Gram-positive pathogens. However, the outer membrane of Gram-negative bacteria does not allow pediocin access to its target. In this work, the synergistic inhibitory mechanism of PA-1 with L-lactic acid against Gram-negative aquaculture and food pathogen Aeromonas hydrophila (A. hydrophila) was analyzed. The combined treatment of 3.5 mmol/L L-lactic acid and 50 μmol/L (or 30 μmol/L) PA-1 had strong bacteriostatic and bactericidal activity against A. hydrophila. Full wavelength scanning and ELISA assay revealed the release of lipopolysaccharide (LPS) from the outer membrane of A. hydrophila caused by L-lactic acid treatment. Laser confocal microscopic imaging of A. hydrophila with FITC-labeled pediocin PA-1 proved the accumulation of PA-1 on lactic acid-treated bacterial cells. PA-1 then caused a rapid dissipation of membrane potential (Δψ) and a proton gradient difference (ΔpH) in lactic acid-treated A. hydrophila. Pediocin PA-1 also caused an increase in the extracellular ATP level. Morphology revealed by SEM and TEM showed that combined treating with lactic acid and PA-1 induced vesicles on the cell surface, the outer and inner membrane disruption, and even cytoplasm leakage and cell lysis. The results proved a potential mechanism of the synergistic inhibition of lactic acid and PA-1 against A. hydrophila, by which L-lactic acid released the outer membrane LPS, making it possible for PA-1 to contact the plasma membrane of A. hydrophila, resulting in the dissipation of proton-motive force in the inner membrane and cell death.

Large microbiota survey reveals how the microbial ecology of cooked ham is shaped by different processing steps

Cooked ham production involves numerous steps shaping the microbial communities of the final product, with consequences on spoilage metabolites production. To identify the main factors driving the ecology of ham and its spoilage, we designed a study encompassing five variables related to ham production: type of storage during meat transportation, churning speed, drain-off time, slicing line and O₂ packaging permeability. About 200 samples from the same facility were obtained and characterized with respect to i) their microbiota based on gyrB amplicon sequencing ii) their production of spoilage-related metabolites based on E-Nose analysis and enzymatic assays. The slicing was the most critical step, shaping two general types of microbiota according to the slicing line: one dominated by Carnobacterium divergens and another one dominated by Leuconostoc carnosum and Serratia proteamaculans. Regarding metabolites production, L. carnosum was associated to d-lactic acid, ethanol and acetic acid production, whereas Serratia proteamaculans was associated to acetic acid production. This last species prevailed with highly O₂-permeable packaging. Within a given slicing line, campaign-based variations were observed, with Lactobacillus sakei, Leuconostoc mesenteroides and Carnobacterium maltaromaticum prevalent in summer. L. sakei was associated with l-lactic acid production and C. maltaromaticum with formic and acetic acid productions.