Use of microbial antagonism to reduce pathogen levels on produce and meat products: a review

Role of Exposure to Lactic Acid Bacteria from Foods of Animal Origin in Human Health

Animal products, in particular dairy and fermented products, are major natural sources of lactic acid bacteria (LAB). These are known for their antimicrobial properties, as well as for their roles in organoleptic changes, antioxidant activity, nutrient digestibility, the release of peptides and polysaccharides, amino acid decarboxylation, and biogenic amine production and degradation. Due to their antimicrobial properties, LAB are used in humans and in animals, with beneficial effects, as probiotics or in the treatment of a variety of diseases. In livestock production, LAB contribute to animal performance, health, and productivity. In the food industry, LAB are applied as bioprotective and biopreservation agents, contributing to improve food safety and quality. However, some studies have described resistance to relevant antibiotics in LAB, with the concomitant risks associated with the transfer of antibiotic resistance genes to foodborne pathogens and their potential dissemination throughout the food chain and the environment. Here, we summarize the application of LAB in livestock and animal products, as well as the health impact of LAB in animal food products. In general, the beneficial effects of LAB on the human food chain seem to outweigh the potential risks associated with their consumption as part of animal and human diets. However, further studies and continuous monitorization efforts are needed to ensure their safe application in animal products and in the control of pathogenic microorganisms, preventing the possible risks associated with antibiotic resistance and, thus, protecting public health.

Guidance on date marking and related food information: part 1 (date marking)

A risk-based approach was developed to be followed by food business operators (FBO) when deciding on the type of date marking (i.e. 'best before' date or 'use by' date), setting of shelf-life (i.e. time) and the related information on the label to ensure food safety. The decision on the type of date marking needs to be taken on a product-by-product basis, considering the relevant hazards, product characteristics, processing and storage conditions. The hazard identification is food product-specific and should consider pathogenic microorganisms capable of growing in prepacked temperature-controlled foods under reasonably foreseeable conditions. The intrinsic (e.g. pH and aw), extrinsic (e.g. temperature and gas atmosphere) and implicit (e.g. interactions with competing background microbiota) factors of the food determine which pathogenic and spoilage microorganisms can grow in the food during storage until consumption. A decision tree was developed to assist FBOs in deciding the type of date marking for a certain food product. When setting the shelf-life, the FBO needs to consider reasonably foreseeable conditions of distribution, storage and use of the food. Key steps of a case-by-case procedure to determine and validate the shelf-life period are: (i) identification of the relevant pathogenic/spoilage microorganism and its initial level, (ii) characterisation of the factors of the food affecting the growth behaviour and (iii) assessment of the growth behaviour of the pathogenic/spoilage microorganism in the food product during storage until consumption. Due to the variability between food products and consumer habits, it was not appropriate to present indicative time limits for food donated or marketed past the 'best before' date. Recommendations were provided relating to training activities and support, using 'reasonably foreseeable conditions', collecting time-temperature data during distribution, retail and domestic storage of foods and developing Appropriate Levels of Protection and/or Food Safety Objectives for food-pathogen combinations.

Evaluation of factors influencing the growth of non-toxigenic Clostridium botulinum type E and Clostridium sp. in high-pressure processed and conditioned tender coconut water from Thailand

Bacterial spores survive high pressure processing (HPP). Group II Clostridium botulinum is an obligate anaerobe spore-forming pathogen that can produce the botulinum neurotoxin under refrigeration. This study assessed nontoxigenic type E C. botulinum and Group II Clostridium sp. growth in raw and HPP (550 MPa, 3 min, 10 °C) Thai coconut water (CCW; pH 5.2). No spore germination or growth occurred in HPP CCW inoculated with 10⁵ CFU/ml after 61 days regardless of oxygen concentration (<0.5 - 11 mg/l) or storage temperature (4 and 20 °C). Spore concentration decreased by 3.0 ± 0.1 log CFU/ml in a worst-case scenario consisting of non-HPP filter-sterilized CCW (pH 7.0) under anoxic incubation at 30 °C during 61 days, suggesting spore germination followed by cellular death. Supplementing filter-sterilized CCW (pH 7.0) with selected germinants and free amino acids did not support spore development, but the addition of nutrient-rich laboratory media (TPGY broth) at low concentrations (6.25%) promoted growth, suggesting that a lack of nutrients prevents C. botulinum development in CCW. Further risk assessment will require evaluating other CCW varieties and toxin production.

Modulations of growth performance, gut microbiota, and inflammatory cytokines by trehalose on Salmonella Typhimurium-challenged broilers

Salmonellosis in broilers is not merely a significant disease with high economic costs in the poultry industry but also the foodborne disease with the impact on public health by cross-contamination. This study was to investigate the prebiotic ability of trehalose supplementing in diets (0, 1, 3, and 5%, w/w) against Salmonella by using S. Typhimurium (ST)-inoculated broilers. The improvements (P < 0.05) of feed conversion ratio (FCR) were observed with 5% trehalose supplementation in ST-inoculated broilers' diets. An addition of 3 or 5% trehalose in diets increased (P < 0.05) the abundance of lactobacilli in the duodenum and jejunum but decreased (P < 0.05) the growth of ST in the cecum. The adverse effects on serum levels of aspartate aminotransferase, triglyceride, and albumin and globulin ratio in ST-inoculated broilers were noticed and counteracted by supplementing 3 or 5% trehalose in diets (P < 0.05). Besides, the inclusion of trehalose in diets alleviated the intestinal damages and maintained the integrity of cecal epithelial cells after ST challenge under an haematoxylin and eosin-staining observation. Supplementing trehalose further showed the inhibitions of toll-like receptor 4-mediated nuclear factor-kappa-B pathway, including the downregulation (P < 0.05) of proinflammatory cytokine genes, such as interleukin 1 beta and lipopolysaccharide-induced tumor necrosis factor-alpha factor and the upregulation (P < 0.05) of interleukin 10 and interferon-alpha in ST-inoculated broilers. Overall, supplementing trehalose alleviated the adverse effects from ST challenge on FCR, serum biochemistry, the damage, and inflammation in the liver and cecum. Those improvements on ST challenged broilers also contributed to the overgrowth of lactobacilli, the decrement of ST, and anti-inflammatory effects in affected broilers. Trehalose, therefore, could be a promising prebiotic against salmonellosis to benefit broiler production and promote food safety in the poultry industry.

Synergistic Effects of Probiotics and Phytobiotics on the Intestinal Microbiota in Young Broiler Chicken

Probiotics and phytobiotics have been studied as in-feed antibiotic alternatives for decades, yet there are no studies on their possible symbiotic effects. In the present study, newly hatched chickens were fed with feeds supplemented either with host-specific Lactobacillus strains (L. agilis and L. salivarius), commercial phytobiotics, or combinations of both. After 13 days of life, crops and caecums were analyzed for bacterial composition (16S rDNA sequencing, qPCR) and activity (bacterial metabolites). Crop and caecum samples were also used to study the ex vivo survival of a broiler-derived extended-spectrum beta-lactamase (ESBL) producing Escherichia coli strain. In the crop, combinations of probiotics and phytobiotics, but not their single application, increased the dominance of lactobacilli. The single application of phytobiotics reduced the metabolite concentrations in the crop, but certain combinations synergistically upregulated the metabolites. Changes in the qualitative and quantitative composition of the caecal microbiota were less pronounced than in the crop. Acetate concentrations were significantly lower for phytobiotics or the L. agilis probiotic strain compared to the control group, but the L. salivarius probiotic showed significantly higher acetate concentrations alone or in combination with one phytobiotic. The synergistic effects on the reduction of the ex vivo survival of an ESBL producing E. coli strain in crop or caecum contents were also observed for most combinations. This study shows the beneficial synergistic effects of probiotics and phytobiotics on the intestinal bacterial composition and their metabolic activity in young broilers. The reduced survival of potentially problematic bacteria, such as ESBL-producing E. coli further indicates that combinations of probiotics and phytobiotics may lead to a more enhanced functionality than their individual supplementation.

Effect of Lactobacillus rhamnosus NCDC 298 with FOS in Combination on Viability and Toxin Production of Enterotoxigenic Escherichia coli

The present study was to investigate the utilization of prebiotics by Lactobacillus rhamnosus NCDC 298 and its synergistic adversary effect on both population and production of heat-labile (LT) toxin in enterotoxigenic Escherichia coli (ETEC). To select suitable prebiotic in order to enhance functionality, its utilization and the prebiotic activity score was examined. Antivirulence effect on ETEC was inspected by its inactivation rate and heat-labile toxin production in presence of different synbiotic combination. L. rhamnosus NCDC 298 strain grown well on media supplemented with fructooligosaccharides (FOS) and galactooligosaccharides (GOS), whereas significant inactivation of ETEC was observed when FOS was added to the co-culture medium. Significant decrease in LT enterotoxin was seen through GM1 ganglioside enzyme linked immunoassay (GM1 ELISA), when ETEC has grown with L. rhamnosus NCDC 298 and FOS. Short-chain FOS proved to be the most effective substrate, improving antagonistic activity for L. rhamnosus NCDC 298. Both L. rhamnosus NCDC 298 with FOS can be used as an effective synbiotic combination for secretory antidiarrheal fermented dairy formulations.

Co-fermentation of Propionibacterium freudenreichii and Lactobacillus brevis in Wheat Bran for in situ Production of Vitamin B12

The present study investigated the effect of co-fermentation on vitamin B12 content and microbiological composition of wheat bran. Propionibacterium freudenreichii DSM 20271 was used as the producer of vitamin while Lactobacillus brevis ATCC 14869 was selected to ensure the microbial safety of the bran dough. Fermentation trials were conducted in bioreactors to monitor and adjust the pH of the ferments. Vitamin B12 level reached 357 ± 8 ng/g dry weight (dw) after 1 day of pH-controlled fermentation with P. freudenreichii monoculture and remained stable thereafter. In co-fermentation with L. brevis, slightly less vitamin B12 (255 ± 31 ng/g dw) was produced in 1 day and an effective inhibition of the growth of total Enterobacteriaceae and Bacillus cereus was obtained. On day 3, vitamin B12 content in pH-controlled co-fermentation increased to 332 ± 44 ng/g dw. On the other hand, without a pH control, co-fermentation resulted in a stronger inhibition of Enterobacteriaceae and B. cereus but a lower level of vitamin B12 (183 ± 5 ng/g dw on day 3). These results demonstrated that wheat bran fermented by P. freudenreichii and L. brevis can be a promising way to produce vitamin B12 fortified plant-origin food ingredients, which could reduce cereal waste streams and contribute to a more resilient food chain.

Protective effects of indigenous Escherichia coli against a pathogenic E. coli challenge strain in pigs

To investigate the inhibitory effect of indigenous enterobacteria on pathogenic Escherichia coli, a challenge trial with postweaning pigs was conducted. A pathogenic E. coli strain was administered to all animals and their health was closely monitored thereafter. Faecal samples were taken from three healthy and three diarrhoeic animals. Samples were cultivated on MacConkey agar and isolates were subcultured. A soft agar overlay assay was used to determine the inhibitory activity of the isolates. A total of 1,173 enterobacterial isolates were screened for their ability to inhibit the E. coli challenge strain. Colony forming units of enterobacteria on MacConkey agar were not different between healthy and diarrhoeic animals in the original samples. Furthermore, numbers of isolates per animal were also not significantly different between healthy (482 isolates) and diarrhoeic animals (691 isolates). A total of 43 isolates (3.7%) with inhibitory activity against the pathogenic E. coli challenge strain were detected. All inhibitory isolates were identified as E. coli via MALDI-TOF. The isolates belonged to the phylotypes A, C and E. Many isolates (67.4%) were commensal E. coli without relevant porcine pathogenic factors, but toxin- and fimbrial genes (stx2e, fae, estIb, elt1a, fas, fan) were detected in 14 inhibitory isolates. Healthy animals showed significantly (P=0.003) more inhibitory isolates (36 of 482 isolates; 7.5%) than diseased animals (7 of 691 isolates; 1.0%). There were no significant correlations regarding phylotype or pathogenic factors between healthy and diseased animals. This study has shown that a small proportion of indigenous E. coli is able to inhibit in vitro growth of a pathogenic E. coli strain in pigs. Furthermore, healthy animals possess significantly more inhibitory E. coli strains than diarrhoeic animals. The inhibition of pathogenic E. coli by specific indigenous E. coli strains may be an underlying principle for the containment of pathogenic E. coli in pigs.

Strand-specific transcriptomes of Enterohemorrhagic Escherichia coli in response to interactions with ground beef microbiota: interactions between microorganisms in raw meat

BACKGROUND

Enterohemorrhagic Escherichia coli (EHEC) are zoonotic agents associated with outbreaks worldwide. Growth of EHEC strains in ground beef could be inhibited by background microbiota that is present initially at levels greater than that of the pathogen E. coli. However, how the microbiota outcompetes the pathogenic bacteria is unknown. Our objective was to identify metabolic pathways of EHEC that were altered by natural microbiota in order to improve our understanding of the mechanisms controlling the growth and survival of EHECs in ground beef.

RESULTS

Based on 16S metagenomics analysis, we identified the microbial community structure in our beef samples which was an essential preliminary for subtractively analyzing the gene expression of the EHEC strains. Then, we applied strand-specific RNA-seq to investigate the effects of this microbiota on the global gene expression of EHEC O2621765 and O157EDL933 strains by comparison with their behavior in beef meat without microbiota. In strain O2621765, the expression of genes connected with nitrate metabolism and nitrite detoxification, DNA repair, iron and nickel acquisition and carbohydrate metabolism, and numerous genes involved in amino acid metabolism were down-regulated. Further, the observed repression of ftsL and murF, involved respectively in building the cytokinetic ring apparatus and in synthesizing the cytoplasmic precursor of cell wall peptidoglycan, might help to explain the microbiota's inhibitory effect on EHECs. For strain O157EDL933, the induced expression of the genes implicated in detoxification and the general stress response and the repressed expression of the peR gene, a gene negatively associated with the virulence phenotype, might be linked to the survival and virulence of O157:H7 in ground beef with microbiota.

CONCLUSION

In the present study, we show how RNA-Seq coupled with a 16S metagenomics analysis can be used to identify the effects of a complex microbial community on relevant functions of an individual microbe within it. These findings add to our understanding of the behavior of EHECs in ground beef. By measuring transcriptional responses of EHEC, we could identify putative targets which may be useful to develop new strategies to limit their shedding in ground meat thus reducing the risk of human illnesses.

Plant Community Richness Mediates Inhibitory Interactions and Resource Competition between Streptomyces and Fusarium Populations in the Rhizosphere

Plant community characteristics impact rhizosphere Streptomyces nutrient competition and antagonistic capacities. However, the effects of Streptomyces on, and their responses to, coexisting microorganisms as a function of plant host or plant species richness have received little attention. In this work, we characterized antagonistic activities and nutrient use among Streptomyces and Fusarium from the rhizosphere of Andropogon gerardii (Ag) and Lespedeza capitata (Lc) plants growing in communities of 1 (monoculture) or 16 (polyculture) plant species. Streptomyces from monoculture were more antagonistic against Fusarium than those from polyculture. In contrast, Fusarium isolates from polyculture had greater inhibitory capacities against Streptomyces than isolates from monoculture. Although Fusarium isolates had on average greater niche widths, the collection of Streptomyces isolates in total used a greater diversity of nutrients for growth. Plant richness, but not plant host, influenced the potential for resource competition between the two taxa. Fusarium isolates had greater niche overlap with Streptomyces in monoculture than polyculture, suggesting greater potential for Fusarium to competitively challenge Streptomyces in monoculture plant communities. In contrast, Streptomyces had greater niche overlap with Fusarium in polyculture than monoculture, suggesting that Fusarium experiences greater resource competition with Streptomyces in polyculture than monoculture. These patterns of competitive and inhibitory phenotypes among Streptomyces and Fusarium populations are consistent with selection for Fusarium-antagonistic Streptomyces populations in the presence of strong Fusarium resource competition in plant monocultures. Similarly, these results suggest selection for Streptomyces-inhibitory Fusarium populations in the presence of strong Streptomyces resource competition in more diverse plant communities. Thus, landscape-scale variation in plant species richness may be critical to mediating the coevolutionary dynamics and selective trajectories for inhibitory and nutrient use phenotypes among Streptomyces and Fusarium populations in soil, with significant implications for microbial community functional characteristics.

Microbes versus microbes: control of pathogens in the food chain

Foodborne illness continues as a considerable threat to public health. Despite improved hygiene management systems and increased regulation, pathogenic bacteria still contaminate food, causing sporadic cases of illness and disease outbreaks worldwide. For many centuries, microbial antagonism has been used in food processing to improve food safety. An understanding of the mode of action of this microbial antagonism has been gained in recent years and potential applications in food and feed safety are now being explored. This review focuses on the potential opportunities presented, and the limitations, of using microbial antagonism as a biocontrol mechanism to reduce contamination along the food chain; including animal feed as its first link. © 2014 Society of Chemical Industry.

Growth of Shiga toxin-producing Escherichia coli (STEC) and impacts of chilling and post-inoculation storage on STEC attachment to beef surfaces

Concern has been expressed surrounding the utility of studies describing the efficacy of antimicrobial interventions targeting the Shiga toxin-producing Escherichia coli (STEC) that inoculate chilled versus non-chilled beef carcasses. The objectives of this study were to evaluate the effects of chilling (non-chilled, chilled to surface temperature of ≤5 °C) on STEC attachment to brisket surfaces, and the effects of post-inoculation storage on STEC recovery. Paired briskets from split carcasses were separated; one brisket from each pair was kept non-chilled, while the other was chilled to a surface temperature of ≤5 °C prior to inoculation. Briskets were inoculated with a cocktail of eight STEC and then stored at 5 or 25 °C. At 0, 30, 60, 90 and 120 min post-inoculation, 30 cm(2) of tissue was aseptically excised, followed by selective enumeration of strongly and loosely attached STEC. A significant, though small (0.4 log10 CFU/cm(2)), difference in the numbers of strongly attached cells was observed between non-chilled and chilled briskets (p < 0.05). Significant effects on cell attachment by the interaction of chilling and post-inoculation storage period, or chilling and post-inoculation storage temperature, were identified (p < 0.05). Results indicate beef chilling and post-inoculation storage conditions influenced STEC attachment to beef.

Draft Genome Sequence of the Pediocin-Encoding Biopreservative and Biocontrol Strain Pediococcus acidilactici D3

We describe a draft genome sequence for Pediococcus acidilactici strain D3, a component of multistrain commercial cultures with biopreservative and biocontrol properties in food-based applications. Strain D3 encodes at least one antimicrobial peptide, pediocin AMPd3. The AMPd3-encoding operon exhibits high sequence similarity to the archetype pediocin, PA-1, encoded by P. acidilactici PAC 1.0.

Growth inhibition of foodborne pathogens by Oenococcus oeni

To explore the possibility of using Oenococcus oeni to inhibit foodborne pathogens, and to characterize antimicrobial compounds produced by O. oeni, 24 strains of O. oeni were tested for their ability to inhibit growth of foodborne pathogens, Escherichia coli O157:H7, Salmonella enteritidis, and Listeria monocytogenes by using the spot-on-lawn method. Of the 24 strains, 17 strains were able to inhibit all 3 pathogens in this study. Proteases, catalase, and buffer solutions were used for determining the type of inhibitory compounds produced from 4 selected strains with stronger inhibitory activity. Antimicrobial activity of 2 strains against the pathogens was completely inactivated by buffer solution, and other 2 strains against E. coli O157:H7 were partially removed. The antimicrobial compound was not sensitive to selected proteases and catalase.

PRACTICAL APPLICATION

There is little information available about using O. oeni for human pathogens control. The results of this study revealed such discovery and potential applications for pathogen control.

Reduction of Escherichia coli O157:H7 in Fresh Spinach, using lactic acid bacteria and chlorine as a multihurdle intervention

A 12-day shelf life study was conducted at 7 degrees C to determine whether Escherichia coli O157:H7 on spinach can be controlled effectively by selected strains of lactic acid bacteria (LAB) alone or in combination with chlorine as a multihurdle intervention. The multihurdle intervention consisted of both LAB and chlorine and was applied to spinach as a rinse and evaluated in comparison to LAB alone and chlorine and water rinses. Reductions achieved by all treatments also were compared with those observed for an inoculated control. The spinach was inoculated by submersion in a solution containing an E. coli O157:H7 cocktail at 1.0 x 10(6) CFU/ml. LAB were applied postharvest at a concentration of 2.0 x 10(8) CFU/ml, and 200 ppm of chlorine was used for the chlorine rinse. All spinach samples were packaged in commercial packaging, held in a retail display case, and tested for E. coli O157:H7 on days 0, 1, 3, 6, 9, and 12 using the Neo-Grid filtration system and CHROMagar. Survival of LAB throughout the shelf life also was determined. Significant reductions in pathogen populations were achieved by water (P = 0.0008), LAB (P < 0.0001), chlorine (P < 0.0001), and multihurdle (P < 0.0001) treatments when compared with controls. The multihurdle treatment produced the greatest reduction from control populations, a reduction of 1.91 log CFU/ml. This reduction was significantly greater than that achieved with water (P < 0.0001), LAB (P = 0.0025), and chlorine (P < 0.0001) alone, indicating that the application of chlorine and LAB is most effective as a combination treatment. The results obtained from this study indicate that the industry standard chlorine wash may be more effective when applied in combination with LAB.

External concentration of organic acid anions and pH: key independent variables for studying how organic acids inhibit growth of bacteria in mildly acidic foods

Although the mechanisms by which organic acids inhibit growth of bacteria in mildly acidic foods are not fully understood, it is clear that intracellular accumulation of anions is a primary contributor to inhibition of bacterial growth. We hypothesize that intracellular accumulation of anions is driven by 2 factors, external anion concentration and external acidity. This hypothesis follows from basic chemistry principles that heretofore have not been fully applied to studies in the field, and it has led us to develop a novel approach for predicting internal anion concentration by controlling the external concentration of anions and pH. This approach overcomes critical flaws in contemporary experimental design that invariably target concentration of either protonated acid or total acid in the growth media thereby leaving anion concentration to vary depending on the pK(a) of the acids involved. Failure to control external concentration of anions has undoubtedly confounded results, and it has likely led to misleading conclusions regarding the antimicrobial action of organic acids. In summary, we advocate an approach for directing internal anion levels by controlling external concentration of anions and pH because it presents an additional opportunity to study the mechanisms by which organic acids inhibit bacterial growth. Knowledge gained from such studies would have important application in the control of important foodborne pathogens such as Listeria monocytogenes, and may also facilitate efforts to promote the survival in foods or beverages of desirable probiotic bacteria.

Bacterial communities associated with retail alfalfa sprouts

Fresh produce, including salad, is increasingly implicated in foodborne outbreaks. Although studies have been carried out to detect specific human pathogens from fresh produce, the total bacterial community associated with fresh produce is poorly understood. In this study, we characterized the bacterial community associated with alfalfa sprouts, using a culture-independent method. Four retail-purchased alfalfa sprout samples were obtained from different producers, and the bacterial community associated with each sample was determined by 16S rDNA profiling. Our results indicate that alfalfa sprouts sampled in our study shared significant similarities in their bacterial communities. Proteobacteria was the dominant phylum detected from all alfalfa sprout samples, with Enterobacteriaceae, Oxalobacteraceae, Moraxellaceae, and Sphingomonadaceae as the most frequently detected families. These results indicate that growth conditions of alfalfa sprouts should be taken into consideration to prevent the proliferation of pathogenic proteobacteria such as Escherichia coli O157 and Salmonella.