Safety of the surrogate microorganism Enterococcus faecium NRRL B-2354 for use in thermal process validation

A meta-analysis of microbial thermal inactivation in low moisture foods

Microbial thermal inactivation in low moisture foods is challenging due to enhanced thermal resistance of microbes and low thermal conductivity of food matrices. In this study, we leveraged the body of previous work on this topic to model key experimental features that determine microbial thermal inactivation in low moisture foods. We identified 27 studies which contained 782 mean D-values and developed linear mixed-effect models to assess the effect of microorganism type, matrix structure and composition, water activity, temperature, and inoculation and recovery methods on cell death kinetics. Intraclass correlation statistics (I2) and conditional R2 values of the linear mixed effects models were: E. coli (R2-0.91, I2-83%), fungi (R2-0.88, I2-85%), L. monocytogenes (R2-0.84, I2-75%), Salmonella (R2-0.69, I2-46%). Finally, global response surface models (RSM) were developed to further study the non-linear effect of aw and temperature on inactivation. The fit of these models varied by organisms from R2 0.88 (E. coli) to 0.35 (fungi). Further dividing the Salmonella data into individual RSM models based on matrix structure improved model fit to R2 0.90 (paste-like products) and 0.48 (powder-like products). This indicates a negative relationship between data diversity and model performance.

Bad to the bone? - Genomic analysis of Enterococcus isolates from diverse environments reveals that most are safe and display potential as food fermentation microorganisms

Enterococci comprise a group of lactic acid bacteria (LAB) with considerable potential to serve as food fermentation microorganisms. Unfortunately, enterococci have received a lot of negative attention, due to the occurrence of pathogenic and multidrug resistant strains. In this study, we used genomics to select safe candidates among the forty-four studied enterococcal isolates. The genomes of the forty-four strains were fully sequenced and assessed for presence of virulence and antibiotic resistance genes. Nineteen isolates belonging to the species Enterococcus lactis, Enterococcus faecium, Enterococcus durans, and Enterococcus thailandicus, were deemed safe from the genome analysis. The presence of secondary metabolite gene clusters for bacteriocins was assessed, and twelve candidates were found to secrete antimicrobial compounds effective against Listeria monocytogenes isolated from cheese and Staphylococcus aureus. Physiological characterization revealed nineteen industrial potentials; all strains grew well at 42 °C and acidified 1.5 hours faster than their mesophilic counterpart Lactococcus lactis, with which they share metabolism and flavor forming ability. We conclude that a large fraction of the examined enterococci were safe and could serve as excellent food fermentation microorganisms with inherent bioprotective abilities.

Evaluation of Enterococcus faecium NRRL B-2354 as a surrogate for Listeria monocytogenes during chlorine and peroxyacetic acid interventions in simulated apple dump tank water

Sanitizers are widely incorporated in commercial apple dump tank systems to mitigate the cross-contamination of foodborne pathogens. This study validated the suitability of Enterococcus faecium NRRL B-2354 as a surrogate for Listeria monocytogenes during sanitizer interventions in dump tank water systems. E. faecium NRRL B-2354 inoculated on apples exhibited statistically equivalent susceptibility to L. monocytogenes when exposed to chlorine-based sanitizers (25-100 ppm free chlorine (FC)) and peroxyacetic acid (PAA, 20-80 ppm) in simulated dump tank water (SDTW) with 1000 ppm chemical oxygen demand (COD), resulting in 0.2-0.9 and 1.1-1.7 log CFU/apple reduction, respectively. Increasing the contact time did not affect sanitizer efficacies against E. faecium NRRL B-2354 and L. monocytogenes on apples. Chlorine and PAA interventions demonstrated statistically similar efficacies against both bacteria inoculated in SDTW. Chlorine at 25 and 100 ppm FC for 0.5-5 min contact yielded ~37.68-78.25 % and > 99.85 % inactivation, respectively, in water with 1000-4000 ppm COD, while ~51.55-99.86 % and > 99.97 % inactivation was observed for PAA at 20 and 80 ppm, respectively. No statistically significant difference was observed between the transference of E. faecium NRRL B-2354 and L. monocytogenes from inoculated apples to uninoculated apples and water, and from water to uninoculated apples during chlorine- or PAA-treated SDTW exposure. The data suggest E. faecium NRRL B-2354 is a viable surrogate for L. monocytogenes in dump tank washing systems, which could be used to predict the anti-Listeria efficacy of chlorine and PAA interventions during commercial apple processing. Further investigations are recommended to assess the suitability of E. faecium NRRL B-2354 as a surrogate for L. monocytogenes, when using different sanitizers and different types of produce to ensure reliable and comprehensive results.

Reduction Foodborne Pathogens and Surrogate Microorganism on Citrus Fruits after Lab- and Pilot-scale Finishing Wax Application

After finishing waxes are applied, citrus fruits are typically dried at 32-60°C for 2-3 min before final packing. The survival of Listeria monocytogenes, Salmonella, and Enterococcus faecium NRRL B-2354 was evaluated under laboratory conditions on lemons after applying one of four finishing waxes (F4, F6, F8, and F15) followed by an ambient hold or heated (50 or 60°C) drying step. The reduction of inoculated microorganisms during drying was significantly influenced by wax type and temperature, with greater reductions at higher temperatures. Greater reductions after waxing and drying at 60°C were observed with L. monocytogenes (2.84-4.44 log) than with Salmonella (1.65-3.67 log), and with Salmonella than with E. faecium (0.99-2.93 log). The survival of Salmonella inoculated at 5.8-5.9 log/fruit on lemons and oranges after applying wax F6 and drying at 60°C was evaluated during storage at 4 and 22°C. The reductions of Salmonella after waxing and drying were 1.7 log; additional reductions during storage at 4 or 22°C were 1.40-1.43 or 0.18-0.29 log, respectively, on waxed lemons, and 0.56-1.02 or 0.54-0.57 log, respectively, on waxed oranges. Under pilot-scale packinghouse conditions with wax F4, mean and minimum reductions of E. faecium ranged from 2.15 to 2.89 and 1.64 to 2.12 log, respectively. However, E. faecium was recovered by whole-fruit enrichment (limit of detection: 0.60 log CFU/lemon) but not by plating (LOD: 1.3 log CFU/lemon) from uninoculated lemons run with or after the inoculated lemons. The findings should provide useful information to establish and implement packinghouse food safety plans.

Inactivation kinetics of selected pathogenic and non-pathogenic bacteria by aqueous ozone to validate minimum usage in purified water

Ozone is often used as an antimicrobial agent at the final step in purified water processing. When used in purified bottled water manufacturing, residual ozone should not exceed 0.4 mg/L, per US-FDA regulations. These regulations require the control of Escherichia coli and other coliform bacteria; however, non-coliform pathogens can contaminate bottled water. Hence, it is prudent to test the efficacy of ozone against such pathogens to determine if the regulated ozone level adequately ensures the safety of the product. Inactivation of selected pathogenic and non-pathogenic bacteria in purified water was investigated as a function of ozone dose, expressed in Ct units (mg O3*min/L). Bacterial species tested were Enterococcus faecium, E. coli (two serotypes), Listeria monocytogenes (three strains), Pseudomonas aeruginosa, and Salmonella enterica (three serovars). Resulting dose (Ct)-response (reduction in populations' log10 CFU/mL) relationships were mostly linear with obvious heteroscedasticity. This heteroscedastic relationship required developing a novel statistical approach to analyze these data so that the lower bound of the dose-response relationships can be determined and appropriate predictive models for such a bound can be formulated. An example of this analysis was determining the 95%-confidence lower bound equation for the pooled dose-responses of all tested species; the model can be presented as follows: Logpopulationreduction = 3.80Ct + 1.84. Based on this relationship, application ozone at a Ct of 0.832 and 21°C achieves ≥ 5-log reduction in the population of any of the tested pathogenic and non-pathogenic bacteria. This dose can be implemented by applying ozone at 0.832 mg/L for 1 min, 0.416 mg/L for 2 min, or other combinations. The study also proved the suitability of E. faecium ATCC 8459 as a surrogate strain for the pathogens tested in the current study for validating water decontamination processes by ozone. In conclusion, the study findings can be usefully implemented in processing validation of purified water and possibly other water types.

Enhanced heat tolerance of freeze-dried Enterococcus faecium NRRL B-2354 as valid Salmonella surrogate in low-moisture foods

In microbial studies of low-moisture foods (LMFs, water activity less than 0.85), freeze-dried bacteria benefit us to inoculate LMFs without introducing extra water or altering food physiochemical properties. However, the freeze-drying process would bring unavoidable damage to bacterial cells and results in less-resistant inoculum that are unlikely to be qualified in microbial studies. Herein, we enhanced bacterial heat tolerance by subjecting the cells to mild heat (42-50 °C) to counteract the reduced heat tolerance and survivability of freeze-dried bacteria. Enterococcus faecium NRRL B-2354 (E. faecium), a Salmonella surrogate in LMFs, was used as the target microorganism because it was widely accepted in microbial validation of thermal pasteurizing LMFs. Three types of LMFs (peanut powder, protein powder, and onion powder) were used as LMFs models to validate the freeze-dried E. faecium in comparison with Salmonella enterica Enteritidis PT 30 (S. Enteritidis) prepared by the traditional aqueous method. The heat tolerance (D65℃ value) of E. faecium increased at all treatments and peaked (+31.48 ± 0.13%) at temperature-time combinations of 45 °C-60 min and 50 °C-5 min. Survivability of freeze-dried inoculum and its heat tolerance retained well within 50 d storage. The freeze-dried E. faecium was prepared in this study brought equal or higher heat tolerance (D85℃ or D75℃) than S. Enteritidis in tested LMFs models. For instance, the D85℃ of freeze-dried E. faecium (heat-treated at 50 °C for 5 min) and S. Enteritidis in whole egg powder are 35.56 ± 1.52 min and 28.41 ± 0.41 min, respectively. The freeze-dried E. faecium with enhanced heat tolerance appears to be a suitable Salmonella surrogate for dry-inoculating LMFs. Our protocol also enables industry-scale production of freeze-dried inoculum by broth-cultivation method combined with mild-heat treatment.

Enterococcus faecium C171: Modulating the Immune Response to Acute Lethal Viral Challenge

Commensal bacteria modulate acute immune responses to infection in hosts. In this study, Enterococcus faecium C171 was screened and isolated. This strain has similar basic characteristics to the reference probiotic, including strong anti-inflammatory and anti-infective effects. E. faecium C171 inhibits the production of pro-Caspase-1 and significantly reduces the production of interleukin-1β (IL-1β) in vitro. These reactions were confirmed using the Transwell system. Live E. faecium C171 mainly exerted an inhibitory effect on acute inflammation, whereas the anti-infective and immune-activating effects were primarily mediated by the E. faecium C171-produced bacterial extracellular vesicles (Efm-C171-BEVs). Furthermore, in the specific pathogen-free (SPF) chicken model, oral administration of E. faecium C171 increased the relative abundance of beneficial microbiota (Enterococcus and Lactobacillus), particularly Enterococcus, the most important functional bacteria of the gut microbiota. E. faecium C171 significantly inhibited the acute inflammatory response induced by a highly virulent infectious disease, and reduced mortality in SPF chickens by 75%. In addition, E. faecium C171 induced high levels of CD3+, CD4-, and CD8- immunoregulatory cells and CD8+ killer T cells, and significantly improved the proliferative activity of T cells in peripheral blood mononuclear cells, and the secretion of interferon-γ. These findings indicate that E. faecium C171 and Efm-C171-BEVs are promising candidates for adjuvant treatment of acute inflammatory diseases and acute viral infections.

Transfer of Enterococcus faecium and Salmonella enterica during simulated postharvest handling of yellow onions (Allium cepa)

Bacterial transfer during postharvest handling of fresh produce provides a mechanism for spreading pathogens, but risk factors in dry environments are poorly understood. The aim of the study was to investigate factors influencing bacterial transfer between yellow onions (Allium cepa) and polyurethane (PU) or stainless steel (SS) under dry conditions. Rifampin-resistant Enterococcus faecium NRRL B-2354 or a five-strain cocktail of Salmonella was inoculated onto onion skin or PU surfaces at high or moderate levels using peptone, onion extract, or soil water as inoculum carriers. Transfer from inoculated to uninoculated surfaces was conducted using a texture analyzer to control force, time, and number of contacts. Transfer rates (ratio of recipient surface to donor surface populations) of E. faecium (4-5%) were significantly higher than those of Salmonella (0.5-0.6%) at the high (7 log CFU/cm2) but not moderate (5 log CFU/cm2) inoculum levels. Significantly higher populations of E. faecium transferred from onion to PU than from PU to onion. The transfer rates of E. faecium were impacted by inoculum carrier (61% [onion extract], 1.6% [peptone], and 0.31% [soil]) but not by inoculation level or recipient surface (PU versus SS). Bacterial transfer during dry onion handling is significantly dependent on bacterial species, inoculation levels, inoculum carrier, and transfer direction.

Phenotypic and genomic analyses of bacteriocin-producing probiotic Enterococcus faecium EFEL8600 isolated from Korean soy-meju

Enterococcus faecium is a prevalent species found in fermented soybean products, known for its contributions to flavor development and inhibition of pathogenic microorganisms during fermentation. This study aims to provide comprehensive phenotypic and genomic evidence supporting the probiotic characteristics of E. faecium EFEL8600, a bacteriocin-producing strain isolated from Korean soy-meju. Phenotypic analysis revealed that EFEL8600 produced a peptide with inhibitory activity against Listeria monocytogenes, estimated to be 4.6 kDa, corresponding to the size of enterocins P or Q. Furthermore, EFEL8600 exhibited probiotic traits, such as resilience in gastrointestinal conditions, antioxidant and anti-inflammatory activities, and protection of the intestinal barrier. Safety assessments demonstrated no hemolytic and bile salt deconjugation activities. Genomic analysis revealed the presence of several genes associated with probiotic characteristics and bacteriocin production, while few deleterious genes with a low likelihood of expression or transferring were detected. Overall, this study highlights E. faecium EFEL8600 as a potent anti-listeria probiotic strain suitable for use as a starter culture in soymilk fermentation, providing potential health benefits to consumers.

Progress in the application of Enterococcus faecium in animal husbandry

As a probiotic, enterococcus faecium (E. faecium) has the characteristics of high temperature resistance, gastric acid resistance, bile salt resistance, etc. It can also effectively improve animal performance and immunity and improve the animal's intestinal environment, so in recent years it has been more widely used in the livestock industry. However, due to the improper use of antibiotics and the growing environmental stress of strains, the drug resistance of enterococcus faecium has become more and more serious, and because some enterococcus faecium carry virulence genes, leading to the emergence of pathogenic strains, its safety issues have been widely concerned. This paper focuses on the biological characteristics of enterococcus faecium, the application of this bacterium in animal husbandry and the safety issues in its use, with a view to providing a reference for the application of enterococcus faecium in the development of animal husbandry.

Genomic insights into antibiotic-resistance and virulence genes of Enterococcus faecium strains from the gut of Apis mellifera

Enterococcus faecium is a lactic acid bacterium that confers beneficial health effects in humans. However, lately, a number of E. faecium strains have been linked to the spread of nosocomial infections in the hospital environment. Therefore, any potential commercial usage of E. faecium isolates should be preceded by an assessment of infection risk. In the current study, the genomes of two novel E. faecium strains Am1 (larval isolate) and Bee9 (adult bee isolate) isolated from the gut of Apis mellifera L. (honeybee) were sequenced to allow evaluation of their safety. In particular, their genomes were screened for antibiotic-resistance and virulence genes. In addition, their potential to spread resistance in the environment was evaluated. The analysis revealed that Am1 and Bee9 possess 2832 and 2844 protein-encoding genes, respectively. In each case, the genome size was 2.7 Mb with a G+C content of 37.9 mol%. Comparative analysis with probiotic, non-pathogenic and pathogenic enterococci revealed that there are variations between the two bee E. faecium isolates and pathogenic genomes. They were, however, closely linked to the probiotic comparison strains. Phenotypically, the Am1 and Bee9 strains were susceptible to most antibiotics tested, but showed intermediate sensitivity towards erythromycin, linezolid and trimethoprim/sulfamethoxazole. Notably, no genes associated with antibiotic resistance in clinical isolates (e.g. vancomycin resistance: vanA, vanB, vanS, vanX and vanY) were present. In addition, the insertion sequences (IS16, ISEfa11 and ISEfa5), acting as molecular pathogenicity markers in clinically relevant E. faecium strains, were also absent. Moreover, the analysis revealed the absence of three key pathogenicity-associated genes (acm, sgrA, ecbA) in the Am1 and Bee9 strains that are found in the prominent clinical isolates DO, V1836, Aus0004 and Aus0085. Overall, the findings of this investigation suggest that the E. faecium isolates from the bee gut have not suffered any recent clinically relevant antibiotic exposure. It also suggests that E. faecium Am1 and Bee9 are safe potential probiotic strains, because they lack the phenotypic and genetic features associated with strains eliciting nosocomial infections.

Interlaboratory Evaluation of Enterococcus faecium NRRL B-2354 as a Salmonella Surrogate for Validating Thermal Treatment of Multiple Low-Moisture Foods

ABSTRACT

This multi-institutional study assessed the efficacy of Enterococcus faecium NRRL B-2354 as a nonpathogenic Salmonella surrogate for thermal processing of nonfat dry milk powder, peanut butter, almond meal, wheat flour, ground black pepper, and date paste. Each product was analyzed by two laboratories (five independent laboratories total), with the lead laboratory inoculating (E. faecium or a five-strain Salmonella enterica serovar cocktail of Agona, Reading, Tennessee, Mbandaka, and Montevideo) and equilibrating the product to the target water activity before shipping. Both laboratories subjected samples to three isothermal treatments (between 65 and 100°C). A log-linear and Bigelow model was fit to survivor data via one-step regression. On the basis of D80°C values estimated from the combined model, E. faecium was more thermally resistant (P < 0.05) than Salmonella in nonfat dry milk powder (DEf-80°C, 100.2 ± 5.8 min; DSal-80°C, 28.9 ± 1.0 min), peanut butter (DEf-80°C, 133.5 ± 3.1 min; DSal-80°C, 57.6 ± 1.5 min), almond meal (DEf-80°C, 34.2 ± 0.4 min; DSal-80°C, 26.1 ± 0.2 min), ground black pepper (DEf-80°C, 3.2 ± 0.8 min; DSal-80°C, 1.5 ± 0.1 min), and date paste (DEf-80°C, 1.5 ± 0.0 min; DSal-80°C, 0.5 ± 0.0 min). Although the combined laboratory D80°C for E. faecium was lower (P < 0.05) than for Salmonella in wheat flour (DEf-80°C, 9.4 ± 0.1 min; DSal-80°C, 10.1 ± 0.2 min), the difference was ∼7%. The zT values for Salmonella in all products and for E. faecium in milk powder, almond meal, and date paste were not different (P > 0.05) between laboratories. Therefore, this study demonstrated the impact of standardized methodologies on repeatability of microbial inactivation results. Overall, E. faecium NRRL B-2354 was more thermally resistant than Salmonella, which provides support for utilizing E. faecium as a surrogate for validating thermal processing of multiple low-moisture products. However, product composition should always be considered before making that decision.

HIGHLIGHTS

Superheated steam effectively inactivates diverse microbial targets despite mediating effects from food matrices in bench-scale assessments

Sanitation in dry food processing environments is challenging due to the exclusion of water. Superheated steam (SHS) is a novel sanitation technique that utilizes high temperature steam to inactivate microorganisms. The high sensible heat of SHS prevents condensation on surfaces. Here we evaluated SHS thermal inactivation of various vegetative and spore forming bacteria and fungi and determined the effect of food matrix composition on SHS efficacy. Capillary tubes with vegetative cells (Salmonella, E. coli O157:H7, Listeria monocytogenes, or Enterococcus faecium), Aspergillus fischeri ascospores, or B. cereus spores (100 μL) were SHS treated at 135 ± 1 °C for 1 or 2 s. After 1 s, SHS achieved a reduction of 10.91 ± 0.63 log₁₀ CFU/mL for vegetative cells, 2.09 ± 0.58 log₁₀ ascospores/mL for A. fischeri, and 0.21 ± 0.10 log₁₀ spores/mL for B. cereus. SHS treatment achieved significant reductions in vegetative cells and fungal ascospores (p < 0.05), however B. cereus spores were not significantly reduced after 2 s and were determined to be the most resistant of the cell types evaluated. Consequently, peanut butter compositions (peanut powder, oil, and water) and milk powder (whole and nonfat) inoculated with B. cereus spores on aluminum foil coupons (2 × 3 × 0.5 cm) were tested. The D_161°C values for B. cereus spores ranged from 46.53 ± 4.48 s (6 % fat, 55 % moisture, a_w: 0.927) to 79.21 ± 14.87 s (43 % fat, 10 % moisture, a_w: 0.771) for various peanut butter compositions. Whole milk powder had higher D_161°C (34.38 ± 20.90 s) than nonfat milk powder (24.73 ± 6.78 s). SHS (135 ± 1 °C) rapidly (1 s) inactivated most common vegetative bacterial cells; however B. cereus spores were more heat resistant. B. cereus spore inactivation was significantly affected by product composition (p < 0.05). Compared to the log-linear model (R² 0.81-0.97), the Weibull model had better fit (R² 0.94-0.99). Finally, the ease of peanut butter removal from surfaces increased while the ease of non-fat dry milk removal decreased with the increasing SHS treatment duration. However, allergen residues were detectable on surfaces regardless of SHS treatment. The findings from this study can inform the development of pilot-scale research on SHS.

Investigation on Potential ESKAPE Surrogates for 222 and 254 nm Irradiation Experiments

Background

Due to the increase in multidrug-resistant pathogens, it is important to investigate further antimicrobial options. In order not to have to work directly with pathogens, the investigation of possible surrogates is an important aspect. It is examined how suitable possible surrogate candidates for ESKAPE pathogens are for UVC applications. In addition, the inactivation sensitivities to 222 and 254 nm radiation are compared in relation.

Methods

Non-pathogenic members (Enterococcus mundtii, Staphylococcus carnosus, Acinetobacter kookii, Pseudomonas fluorescens and Escherichia coli) of genera of ESKAPE strains were photoinactivated in PBS with irradiation wavelengths of 222 and 254 nm (no non-pathogenic Klebsiella was available). Log reduction doses were determined and compared to published photoinactivation results on ESKAPE pathogens. It was assumed that non-pathogenic bacteria could be designated as surrogates for one wavelength and one ESKAPE strain, if the doses were between the 25 and 75% quantiles of published log reduction dose of the corresponding pathogen.

Results

For all non-pathogen relatives (except A. kookii), higher average log reduction doses were required for irradiation at 222 nm than at 254 nm. Comparison by boxplot revealed that five of eight determined log reduction doses of the possible surrogates were within the 25 and 75% quantiles of the data for ESKAPE pathogens. The measured log reduction dose for non-pathogenic E. coli was above the 75% quantile at 222 nm, and the log reduction dose for S. carnosus was below the 25% quantile at 254 nm.

Conclusion

For more than half of the studied cases, the examined ESKAPE relatives in this study can be applied as surrogates for ESKAPE pathogens. Because of lack of data, no clear statement could be made for Enterococcus faecalis at 222 nm and Acinetobacter baumannii at both wavelengths.

Extracellular electron transfer increases fermentation in lactic acid bacteria via a hybrid metabolism

Energy conservation in microorganisms is classically categorized into respiration and fermentation; however, recent work shows some species can use mixed or alternative bioenergetic strategies. We explored the use of extracellular electron transfer for energy conservation in diverse lactic acid bacteria (LAB), microorganisms that mainly rely on fermentative metabolism and are important in food fermentations. The LAB Lactiplantibacillus plantarum uses extracellular electron transfer to increase its NAD⁺/NADH ratio, generate more ATP through substrate-level phosphorylation, and accumulate biomass more rapidly. This novel, hybrid metabolism is dependent on a type-II NADH dehydrogenase (Ndh2) and conditionally requires a flavin-binding extracellular lipoprotein (PplA) under laboratory conditions. It confers increased fermentation product yield, metabolic flux, and environmental acidification in laboratory media and during kale juice fermentation. The discovery of a single pathway that simultaneously blends features of fermentation and respiration in a primarily fermentative microorganism expands our knowledge of energy conservation and provides immediate biotechnology applications.

Bacteria produce the energy they need to live through two processes, respiration and fermentation. While respiration is often more energetically efficient, many bacteria rely on fermentation as their sole means of energy production. Respiration normally depends on the presence of small soluble molecules, such as oxygen, that can diffuse inside the cell, but some bacteria can use metals or other insoluble compounds found outside the cell to perform ‘extracellular electron transfer’.

Lactic acid bacteria are a large group of bacteria that have several industrial uses and live in many natural environments. These bacteria survive using fermentation, but they also carry a group of genes needed for extracellular electron transfer. It is unclear whether they use these genes for respiration or if they have a different purpose.

Tejedor-Sanz, Stevens et al. used a lactic acid bacterium called Lactiplantibacillus plantarum to study whether and how this group of bacteria use extracellular electron transfer. Analysis of L. plantarum and its effect on its surroundings showed that these bacteria use a hybrid process to produce energy: the cells use aspects of extracellular respiration to increase the yield and efficiency of fermentation. Combining these two approaches may allow L. plantarum to adapt to different environments and grow faster, allowing it to compete against other species.

Tejedor-Sanz, Stevens et al. provide new information on a widespread group of bacteria that are often used in food production and industry. The next step will be to understand how the hybrid system is controlled and how it varies among species. Understanding this process could result in new biotechnologies and foods that are healthier, produce less waste, or have different tastes and textures.

Inactivation of indicator microorganisms and biological hazards by standard and/or alternative processing methods in Category 2 and 3 animal by-products and derived products to be used as organic fertilisers and/or soil improvers

The European Commission requested EFSA to assess if different thermal processes achieve a 5 log10 reduction in Enterococcus faecalis or Salmonella Senftenberg (775W) and (if relevant) a 3 log10 reduction in thermoresistant viruses (e.g. Parvovirus) as well as if different chemical processes achieve a 3 log10 reduction of eggs of Ascaris sp., in eight groups of Category 2 and 3 derived products and animal by-products (ABP). These included (1) ash derived from incineration, co-incineration and combustion; (2) glycerine derived from the production of biodiesel and renewable fuels; (3) other materials derived from the production of biodiesel and renewable fuels; (4) hides and skins; (5) wool and hair; (6) feathers and down; (7) pig bristles; and (8) horns, horn products, hooves and hoof products. Data on the presence of viral hazards and on thermal and chemical inactivation of the targeted indicator microorganisms and biological hazards under relevant processing conditions were extracted via extensive literature searches. The evidence was assessed via expert knowledge elicitation. The certainty that the required log10 reductions in the most resistant indicator microorganisms or biological hazards will be achieved for each of the eight groups of materials mentioned above by the thermal and/or chemical processes was (1) 99-100% for the two processes assessed; (2) 98-100% in Category 2 ABP, at least 90-99% in Category 3 ABP; (3) 90-99% in Category 2 ABP; at least 66-90% in Category 3 ABP; (4) 10-66% and 33-66%; (5) 1-33% and 10-50%; (6) 66-90%; (7) 33-66% and 50-95%; (8) 66-95%, respectively. Data generation on the occurrence and reduction of biological hazards by thermal and/or chemical methods in these materials and on the characterisation of the usage pathways of ABP as organic fertilisers/soil improvers is recommended.

Strain diversity of plant-associated Lactiplantibacillus plantarum

Lactiplantibacillus plantarum (formerly Lactobacillus plantarum) is a lactic acid bacteria species found on plants that is essential for many plant food fermentations. In this study, we investigated the intraspecific phenotypic and genetic diversity of 13 L. plantarum strains isolated from different plant foods, including fermented olives and tomatoes, cactus fruit, teff injera, wheat boza and wheat sourdough starter. We found that strains from the same or similar plant food types frequently exhibited similar carbohydrate metabolism and stress tolerance responses. The isolates from acidic, brine‐containing ferments (olives and tomatoes) were more resistant to MRS adjusted to pH 3.5 or containing 4% w/v NaCl, than those recovered from grain fermentations. Strains from fermented olives grew robustly on raffinose as the sole carbon source and were better able to grow in the presence of ethanol (8% v/v or sequential exposure of 8% (v/v) and then 12% (v/v) ethanol) than most isolates from other plant types and the reference strain NCIMB8826R. Cell free culture supernatants from the olive‐associated strains were also more effective at inhibiting growth of an olive spoilage strain of Saccharomyces cerevisiae. Multi‐locus sequence typing and comparative genomics indicated that isolates from the same source tended to be genetically related. However, despite these similarities, other traits were highly variable between strains from the same plant source, including the capacity for biofilm formation and survival at pH 2 or 50°C. Genomic comparisons were unable to resolve strain differences, with the exception of the most phenotypically impaired and robust isolates, highlighting the importance of utilizing phenotypic studies to investigate differences between strains of L. plantarum. The findings show that L. plantarum is adapted for growth on specific plants or plant food types, but that intraspecific variation may be important for ecological fitness and strain coexistence within individual habitats.

Guidance on validation of lethal control measures for foodborne pathogens in foods

Food manufacturers are required to obtain scientific and technical evidence that a control measure or combination of control measures is capable of reducing a significant hazard to an acceptable level that does not pose a public health risk under normal conditions of distribution and storage. A validation study provides evidence that a control measure is capable of controlling the identified hazard under a worst-case scenario for process and product parameters tested. It also defines the critical parameters that must be controlled, monitored, and verified during processing. This review document is intended as guidance for the food industry to support appropriate validation studies, and aims to limit methodological discrepancies in validation studies that can occur among food safety professionals, consultants, and third-party laboratories. The document describes product and process factors that are essential when designing a validation study, and gives selection criteria for identifying an appropriate target pathogen or surrogate organism for a food product and process validation. Guidance is provided for approaches to evaluate available microbiological data for the target pathogen or surrogate organism in the product type of interest that can serve as part of the weight of evidence to support a validation study. The document intends to help food manufacturers, processors, and food safety professionals to better understand, plan, and perform validation studies by offering an overview of the choices and key technical elements of a validation plan, the necessary preparations including assembling the validation team and establishing prerequisite programs, and the elements of a validation report.

Control of Salmonella in low-moisture foods: Enterococcus faecium NRRL B-2354 as a surrogate for thermal and non-thermal validation

Salmonella has been implicated in multiple foodborne outbreaks and recalls associated with low water activity foods (La_wF). To verify the effectiveness of a process against Salmonella in La_wF, validation using a nonpathogenic surrogate strain is essential. Enterococcus faecium NRRL B-2354 strain has been used as a potential surrogate of Salmonella in different processing of La_wF. However, the survival of Salmonella and E. faecium in La_wF during food processing is a dynamic function of a_w, food composition and structure, processing techniques, and other factors. This review assessed pertinent literature on the thermal and non-thermal inactivation of Salmonella and its presumable surrogate E. faecium in various La_wF and provided an overview of its suitibility in different La_wF. Overall, based on the D-values, survival/reduction, temperature/time to obtain 4 or 5-log reductions, most studies concluded that E. faecium is a suitable surrogate of Salmonella during La_wF processing as its magnitude of resistance was slightly greater or equal (i.e., statistical similar) as compared to Salmonella. Studies also showed its unsuitability which either does not provide a proper margin of safety or being overly resistant and may compromise the quality and organoleptic properties of food. This review provides useful information and guidance for future validation studies of La_wF.

Fate of Salmonella and Enterococcus faecium during Pilot-Scale Spray Drying of Soy Protein Isolate

ABSTRACT

Outbreaks and recalls associated with microbial contamination of powdered foods have raised concern for the safety of the spray-drying process and its products. However, little research on the fate of bacteria during the spray-drying process has been done, leaving much unknown about the risks of contamination in spray dryers. Therefore, quantifying the contamination levels of Salmonella and Enterococcus faecium (as a surrogate) in various locations within a pilot-scale spray dryer can help illustrate the distribution of bacterial contamination, including in the final product. A 10% (w/w) dispersion of water and soy protein isolate was mixed with tryptic soy broth containing yeast extract inoculated with Salmonella enterica serovar Enteritidis phage type 30 (PT30) or E. faecium strain NRRL B-2354. This dispersion was spray dried using a pilot-scale tall-form cocurrent spray dryer at an inlet air temperature of 180, 200, or 220°C. After drying, samples of powder from eight locations within the system were collected or surface swabbed, plated, and enumerated. Spray drying achieved 2.40 to 4.15 and 2.33 to 2.83 log reductions in the concentrations of Salmonella and E. faecium, respectively, in the final powder product accumulated in the dryer's collectors. Salmonella and E. faecium were found in various concentrations in all locations within the spray dryer after a complete drying cycle. Differences in inlet air temperature between 180 and 220°C had no significant effect on the inactivation levels. As a surrogate, E. faecium was more resistant to spray drying than Salmonella. Overall, spray drying is capable of significant bacterial reduction in the final powder product, which can be combined with other hurdle technologies. However, adequate cleaning and sanitization procedures must be taken into consideration to prevent cross-contamination.

HIGHLIGHTS

Evaluation of Enterococcus faecium NRRL B-2354 as a surrogate for Salmonella in ground black pepper at different water activities

Thermal inactivation kinetics of Salmonella in low moisture foods are necessary for developing proper thermal processing parameters for pasteurization. The effect of water activity on thermal inactivation kinetics of Salmonella and Enterococcus faecium NRRL B-2354 in ground black pepper has not been studied previously. Identification of a suitable surrogate assists in conducting in-plant process validations. Ground black pepper was inoculated with a 5-serotype Salmonella cocktail or E. faecium NRRL B-2354, equilibrated to water activities of 0.25, 0.45 or 0.65 in a humidity-controlled chamber, and isothermally treated at different temperatures. The survivor data were used for fitting the log-linear models to obtain the D and z-values of Salmonella and E. faecium in ground black pepper. Modified Bigelow models were developed to evaluate the effects of temperature and water activity on the thermal inactivation kinetics of Salmonella and E. faecium. Water activity and temperature showed significant negative effects on the thermal resistance of Salmonella and E. faecium in ground black pepper. For example, significantly higher D values of Salmonella were observed at water activity of 0.45 (D_70°C = 20.5 min and D_75°C = 7.8 min) compared to water activity of 0.65 (D_70°C = 3.9 min and D_75°C = 2.0 min). D-values of E. faecium were significantly higher than those of Salmonella at all three water activities, indicating that E. faecium is a suitable surrogate for Salmonella in thermal processing validation.

Plant-Scale Validation of Physical Heat Treatment of Poultry Litter Composts Using Surrogate and Indicator Microorganisms for Salmonella

This study selected and used indicator and surrogate microorganisms for Salmonella to validate the processes for physically heat-treated poultry litter compost in litter processing plants. Initially laboratory validation studies indicated that 1.2- to 2.7-log or more reductions of desiccation-adapted Enterococcus faecium NRRL B-2354 were equivalent to > 5-log reductions of desiccation-adapted Salmonella Senftenberg 775/W in poultry litter compost, depending on treatment conditions and compost types. Plant validation studies were performed in one turkey litter compost processor and one laying hen litter compost processor. E. faecium was inoculated at ca.7 log CFU g^-1 into the turkey litter compost and at ca. 5 log CFU g^-1 into laying hen litter compost with respectively targeted moisture contents. The thermal processes in the two plants yielded 2.8 - > 6.4 log CFU g^-1 (> 99.86%) reductions E. faecium of the inoculated. Similarly, for the processing control samples, reductions of presumptive indigenous enterococci were in the order of 1.8-3.7 log CFU g^-1 (98.22% to 99.98%) of the total naturally present. In contrast, there were less reductions of indigenous mesophiles (1.7-2.9 log CFU) and thermophiles (0.4-3.2 log CFU g^-1). More indigenous enterococci were inactivated in the presence of higher moisture in the poultry litter compost. Based on the data collected under the laboratory conditions, the processing conditions in both plants were adequate to reduce any potential Salmonella contamination of processed poultry litter compost by at least 5 logs, even though the processing conditions varied among trials and plants.IMPORTANCE Poultry litter compost, commonly used as a biological soil amendment, is subjected to a physical heat-treatment in industry setting to reduce pathogenic bacteria such as Salmonella and produce a dry product. According to the FDA Food Safety Modernization Act (FSMA) Produce Safety Rule, the thermal process for poultry litter compost should be scientifically validated to satisfy the microbial standard requirement. To the best of our knowledge, this is the first validation study in commercial poultry litter compost processing plants, and our results indicated that Salmonella levels, if present, could be reduced by at least 5 logs based on the reductions of surrogate and indicator microorganisms, even though the processing conditions in these commercial plants varied greatly. Furthermore, both indicator and surrogate microorganisms along with the custom-designed sampler can serve as practical tools for poultry litter compost processors to routinely monitor or validate their thermal processes without introducing pathogens into the industrial environments.

A newly isolated E. thailandicus strain d5B with exclusively antimicrobial activity against C. difficile might be a novel therapy for controlling CDI

Colitis induced by C. difficile is one of the most common and costly healthcare-related infections for humans. Probiotics are one of the most promising approaches for controlling CDI. Here, we presented the isolation, safety, and probiotic property evaluation of a novel E. thailandicus strain, d5B, with effective antimicrobial activity against C. difficile. Strain d5B showed strong bactericidal effects on at least 54C. difficile strains. Safety tests showed that strain d5B was sensitive to clinically important antibiotics, and had no haemolytic and cytotoxic activities. Whole genomic analysis showed strain d5B only contained one aminoglycoside resistance gene located in the chromosome. Moreover, d5B was devoid of functional virulence genes. Finally, strain d5B exhibited probiotic properties, such as tolerance to the gastrointestinal tract, and adhered well to HT-29 cells. In conclusion, the E. thailandicus strain d5B should be investigated further for useful properties as a novel candidate probiotic for controlling CDI.

Verification of peroxyacetic acid treatment against L. monocytogenes on fresh apples using E. faecium NRRL B-2354 as a surrogate in commercial spray-bar operations

Peroxyacetic acid (PAA) is a commonly used antimicrobial in apple spray bar interventions during post-harvest packing. However, limited information is available about its efficacy against foodborne pathogens on fresh apples under commercial packing conditions. In this study, the practical efficacies of PAA against Listeria monocytogenes on fresh apples during spray bar operation at ambient and elevated temperature were validated in three commercial packing facilities using Enterococcus faecium NRRL B-2354 as a surrogate strain. Apples were inoculated with E. faecium at ~6.5 Log₁₀ CFU/apple and subjected to PAA spray bar interventions per commercial packing line practice. At each temperature and contact time intervention combination, 20-24 inoculated apples were processed together with 72-80 non-inoculated apples. Applying 80 ppm PAA at ambient temperature (17-21 °C) achieved a similar log reduction (P > 0.05) of E. faecium on Granny Smith apples (GSA) in three apple packing facilities, which caused 1.12-1.23 and 1.18-1.32 Log₁₀ CFU/apple reductions of E. faecium on GSA for 30-sec and 60-sec intervention, respectively. Increasing the temperature of the PAA solution to 43-45 °C enhanced its bactericidal effect against E. faecium, causing 1.45, 1.86 and 2.19 Log₁₀ CFU/apple reductions in three packing facilities for a 30-sec contact, and 1.50, 2.24, and 2.29 Log₁₀ CFU/apple reductions for a 60-sec contact, respectively. Similar efficacies (P > 0.05) of PAA at both ambient and elevated temperature were also observed on Fuji apples. Spraying PAA on apples at ambient or elevated temperature reduced the level of E. faecium cross-contamination from inoculated apples to non-inoculated apples but could not eliminate cross-contamination. Data from this study provides valuable technical information and a reference point for the apple industry in controlling L. monocytogenes and verifying the effectiveness of their practices.

Genome-based species-specific primers for rapid identification of six species of Lactobacillus acidophilus group using multiplex PCR

Many Lactobacillus species are frequently isolated from dairy products, animal guts, and the vaginas of healthy women. However, sequencing-based identification of isolated Lactobacillus strain is time/cost-consuming and lobor-intensive. In this study, we developed a multiplex PCR method to distinguish six closely related species in the Lactobacillus acidophilus group (L. gasseri, L. acidophilus, L. helveticus, L. jensenii, L. crispatus, and L. gallinarum), which is based on species-specific primer sets. Altogether, 86 genomes of 9 Lactobacillus species from the National Center of Biotechnology Information (NCBI) database were compared to detect species-specific genes and design six species-specific primer sets. The PCR conditions of the individual primer sets were optimized via gradient PCR methods. A final multiplex PCR condition was also optimized for a mixture of all six primer sets mixed. When identifying a single strain, the optimized multiplex PCR method can specifically detect one of the six species, but no band was amplified at least from the other Lactobacillus and Enterococcus species. These results indicated that species-specific primer sets designed from the genome comparison could identify one strain within the six Lactobacillus species by a single PCR reaction. Using the method described here, we will be able to save time, cost, and labor during species identification and screening of commercially important probiotic lactobacilli.

Transcriptome analysis to characterize the genes related to gonad growth and fatty acid metabolism in the sea urchin Strongylocentrotus intermedius

BACKGROUND

Sea urchin gonads of both sexes, commonly termed "roe", are highly valued seafood delicacies, and Strongylocentrotus intermedius is considered one of the tastiest sea urchins. In order to produce high-quality gonads for consumption and clarify the mechanism of gonad growth and development of the sea urchin, more genetic information, especially at the transcriptome level, is needed.

OBJECTIVE

A more thorough understanding of sea urchin gonad growth and development in both sexes could enable regulation of these processes at several stages with the aim of suppressing gametogenesis in order to produce high-quality gonads for consumption.

METHODS

The adult sea urchins S. intermedius were cultured for 3 months, and were sampled for the gonadal transcriptome analysis which has been performed on the RNAs of three male and female adults of S. intermedius in each gonad development stage.

RESULTS

Illumina sequencing raw sequence data was deposited in the NCBI Sequence Read Archive (SRA) database (PRJNA532998). It generated 560,196,356 raw reads and 548,956,944 clean reads were acquired, which were assembled into 107,850 transcripts with 44,124 genes. Comparative analysis showed the differentially expressed genes (DEGs) from 114 to 2566. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were used to determine the functional significance of these DEGs. We have selected 9 genes related to growth and 12 genes related to fatty acid biosynthesis and metabolism in sea urchin gonads.

CONCLUSION

These data for sea urchins were intended to provide markers for gonad growth and development that can be accumulated for use in aquaculture applications.

Effect of Talc as a Dry-Inoculation Carrier on Thermal Resistance of Enterococcus faecium NRRL B-2354 in Almond Meal

HIGHLIGHTS

E. faecium was more thermally resistant in dry- than in wet-inoculated almond meal. Presence of talc affected thermal resistance of E. faecium in almond meal. Use of dry inoculum carriers for thermal validation studies requires further work.

Evaluation of Methods for Inoculating Dry Powder Foods with Salmonella enterica, Enterococcus faecium, or Cronobacter sakazakii

Salmonella and Cronobacter are two bacteria of concern in powdered food ingredients with low water activity, due to their ability to remain viable for long periods of time. There is great interest in studying the survival of these bacteria in powdered foods, but discrepancies have been reported between broth-grown and lawn-grown bacterial cells and their thermal resistance and desiccation tolerance once inoculated onto powdered foods. The purpose of this study was to evaluate three different powdered food inoculation methods, two broth-grown and one lawn-grown. To evaluate these methods on three types of powdered food matrices, Salmonella enterica serovar Typhimurium LT2 (ATCC 700720), Salmonella surrogate Enterococcus faecium (NRRL B-2354), and Cronobacter sakazakii (ATCC 29544) were inoculated onto nonfat dry milk powder, organic soy flour, and all-purpose flour using one of the three previously developed inoculation methods. In the first broth-grown method, labeled broth-grown pelletized inoculation, a bacterial cell pellet was added to powdered foods directly and mixed with a sterile wooden stick. The second broth-grown method, labeled broth-grown spray inoculation, used a chromatography reagent sprayer to spray the bacterial cell suspension onto the powdered foods. The third inoculation method, lawn-grown liquid inoculation, made use of a spot inoculation and a stomacher to incorporate each bacterium into the powdered foods. Results indicated that the method of inoculation of each powder impacted repeatability and bacteria survivability postequilibration (4 to 6 days). Broth-grown spray inoculation, regardless of the powder and bacterium, resulted in the highest log reduction, with an average ∼1-log CFU/g reduction following equilibration. Broth-grown pelletized inoculation resulted in the second-highest log reduction (∼0.79 log CFU/g), and finally, lawn-grown liquid inoculation was the most stable inoculation method of the three, with ∼0.52-log CFU/g reduction. Overall, the results from this inoculation study demonstrate that inoculation methodologies impact the desiccation tolerance and homogeneity of C. sakazakii, E. faecium, and Salmonella Typhimurium LT2.

Assembly and Characterization of a Pathogen Strain Collection for Produce Safety Applications: Pre-growth Conditions Have a Larger Effect on Peroxyacetic Acid Tolerance Than Strain Diversity

Effective control of foodborne pathogens on produce requires science-based validation of interventions and control strategies, which typically involves challenge studies with a set of bacterial strains representing the target pathogens or appropriate surrogates. In order to facilitate these types of studies, a produce-relevant strain collection was assembled to represent strains from produce outbreaks or pre-harvest environments, including Listeria monocytogenes (n = 11), Salmonella enterica (n = 23), shiga-toxin producing Escherichia coli (STEC) (n = 13), and possible surrogate organisms (n = 8); all strains were characterized by whole genome sequencing (WGS). Strain diversity was assured by including the 10 most common S. enterica serotypes, L. monocytogenes lineages I-IV, and E. coli O157 as well as selected "non-O157" STEC serotypes. As it has previously been shown that strains and genetic lineages of a pathogen may differ in their ability to survive different stress conditions, a subset of representative strains for each "pathogen group" (e.g., Salmonella, STEC) was selected and assessed for survival of exposure to peroxyacetic acid (PAA) using strains pre-grown under different conditions including (i) low pH, (ii) high salt, (iii) reduced water activity, (iv) different growth phases, (v) minimal medium, and (vi) different temperatures (21°C, 37°C). The results showed that across the three pathogen groups pre-growth conditions had a larger effect on bacterial reduction after PAA exposure as compared to strain diversity. Interestingly, bacteria exposed to salt stress (4.5% NaCl) consistently showed the least reduction after exposure to PAA; however, for STEC, strains pre-grown at 21°C were as tolerant to PAA exposure as strains pre-grown under salt stress. Overall, our data suggests that challenge studies conducted with multi-strain cocktails (pre-grown under a single specific condition) may not necessarily reflect the relevant phenotypic range needed to appropriately assess different intervention strategies.

Complete Genome Sequence of Enterococcus faecium QU50, a Thermophilic Lactic Acid Bacterium Capable of Metabolizing Xylose

Herein, we report the complete genome sequence of Enterococcus faecium QU50, isolated from Egyptian soil and exhibiting intermediate susceptibility to vancomycin. The genome contains a 2,535,796-bp circular chromosome and two plasmids of 196,595 bp and 17,267 bp.

Herein, we report the complete genome sequence of Enterococcus faecium QU50, isolated from Egyptian soil and exhibiting intermediate susceptibility to vancomycin. The genome contains a 2,535,796-bp circular chromosome and two plasmids of 196,595 bp and 17,267 bp. IS1062-like sequences were not found.