Growth Of Listeria Research Articles

Effects of Fermentation Temperature, Drying Temperature, Caliber Size, Starter Culture, and Sodium Lactate on Listeria monocytogenes Inactivation During Salami Production

The effect of fermentation and drying temperatures, caliber, and sodium lactate on Listeria monocytogenes inactivation was studied in salami, produced in a pilot scale, inoculated with 107 CFU/g of Listeria innocua ATCC® 33090 as a surrogate microorganism for L. monocytogenes. Fermentation temperature varied between 24 and 30°C, drying temperature between 14 and 20°C, caliber between 5.1 and 13.2 cm, and sodium lactate initial concentrations in salamis were 0 and 2%. L. innocua counts, pH and water activity were determined in salamis over time. Sodium lactate (2%) decreased pH drop and Listeria inactivation during fermentation. Baranyi & Roberts equation was used to fit the experimental data and to estimate, for each test condition, inactivation rate (k), initial (Y0), and final counts of L. innocua (YEND). Total inactivation was calculated as Y0 minus YEND (Y0-YEND). Then, using a Box Benkhen experimental design, a quadratic model for k and a two-factor interaction model (2FI) for Y0 − YEND were obtained as functions of fermentation temperature, drying temperature, and caliber size. The models predicted that maximum k and Y0 −YEND, −2.62 ± 0.14 log10 CFU/g/day and 4.5 ± 0.1 log10 CFU/g, respectively, would be obtained fermenting at 30°C and drying at 20°C regardless of caliber. Drying at 14°C allowed Listeria growth until a water activity (aw) of 0.92 was reached. Therefore, if initial Listeria contamination is high (3 log10 CFU/g), drying at low temperatures will compromise product safety.

Investigation of the growth of Listeria in plant-based beverages

The objective of the present study was to evaluate whether the content of sugar, protein, fat, or fibre in commercially available and specially formulated plant-based beverages (oat, soya and pea) influences the growth rates of Listeria. Beverages were inoculated with a strain cocktail of Listeria (approximately 1 × 103 CFU/mL), and the data demonstrated that Listeria could proliferate in all tested beverages. Moreover, varying concentrations of naturally occurring or added sugar (0–3.3%), protein (3.3–5%), fat (1.1–3.5%) and added fibre (0–1.5%) did not have a statistically significant (p > 0.05) impact on the growth rates of Listeria in the tested plant-based beverages. These data suggest that the wide variety of commercial plant-based beverages serve as an ideal medium for the growth of Listeria irrespective of product composition. All the various products tested provided sufficient nutrients to support at least a 2.6-log increase of Listeria within 16 h at room temperature, with some beverages supporting a 3-log increase. Therefore, these data highlight the importance of careful storage and handling of these increasingly varied and popular products.

Reduction and Growth Inhibition of Listeria monocytogenes by Use of Anti-Listerial Nisin, P100 Phages and Buffered Dry Vinegar Fermentates in Standard and Sodium-Reduced Cold-Smoked Salmon.

Cold-smoked salmon are ready-to-eat products that may support the growth of pathogenic Listeria monocytogenes during their long shelf-life. Consumption of such contaminated products can cause fatal listeriosis infections. Another challenge and potential risk associated with CS salmon is their high levels of sodium salt. Excess dietary intake is associated with serious health complications. In the present study, anti-listerial bacteriocin (nisin), P100 bacteriophages (Phageguard L, PGL) and fermentates (Verdad N6, P-NDV) were evaluated as commercial bio-preservation strategies for increased control of L. monocytogenes in standard (with NaCl) and sodium-reduced (NaCl partially replaced with KCl) CS salmon. Treatments of CS salmon with nisin (1 ppm) and PGL (5 × 107 pfu/cm2) separately yielded significant initial reductions in L. monocytogenes (up to 0.7 log) compared to untreated samples. Enhanced additive reductions were achieved through the combined treatments of nisin and PGL. Fermentates in the CS salmon inhibited the growth of Listeria but did not lead to its eradication. The lowest levels of L. monocytogenes during storage were observed in nisin- and PGL-treated CS salmon containing preservative fermentates and stored at 4 °C, while enhanced growth was observed during storage at an abusive temperature of 8 °C. Evaluation of industry-processed standard and sodium-replaced CS salmon confirmed significant effects with up to 1.7 log reductions in L. monocytogenes levels after 34 days of storage of PGL- and nisin-treated CS salmon-containing fermentates. No differences in total aerobic plate counts were observed between treated (PGL and nisin) or non-treated standard and sodium-reduced CS salmon at the end of storage. The microbiota was dominated by Photobacterium, but with a shift showing dominance of Lactococcus spp. and Vagococcus spp. in fermentate-containing samples. Similar and robust reductions in L. monocytogenes can be achieved in both standard and sodium-replaced CS salmon using the bio-preservation strategies of nisin, PGL and fermentates under various and relevant processing and storage conditions.

Control of the Growth of Listeria monocytogenes in Cooked Ham through Combinations of Natural Ingredients.

In the ready-to-eat food industry, Listeria control is mandatory to ensure the food safety of the products since its presence could cause a disease called listeriosis. The objective of the present study was to carry out a challenge test to verify the efficiency of different combinations of natural antimicrobial ingredients against Listeria monocytogenes to be used in ready-to-eat foods. Six different formulations of cooked ham were prepared: a control formulation and five different formulations. An initial inoculation of 2 log cycles was used in the different products, and the growth of Listeria was monitored at different temperatures and times (4 °C for 17 w and 7 °C for 12 w). Control samples showed a progressive growth, reaching 5-6 log after 3 or 4 weeks. The rest of the samples showed constant counts of Listeria during the entire study. Only samples containing 100 ppm nitrite + 250 PPM ascorbic acid + 0.7% PRS-DV-5 did not control the growth of Listeria at 7 °C after 7 w of storage. The results obtained allowed us to classify the cooked ham prepared using natural ingredient combinations as a "Ready-to-eat food unable to support the growth of L. monocytogenes other than those intended for infants and for special medical purposes".

Prevalence of Listeria monocytogenes in milk in Africa: a generalized logistic mixed-effects and meta-regression modelling

Listeria outbreaks and food recalls is on the raise globally. Milk particularly is highly susceptible to Listeria as its production and storage adequately support Listeria growth. The extent of milk contamination with Listeria monocytogenes (Lm) and preventative actions to halt milk associated outbreaks in Africa are unknown. Hence, this study aimed at assessing the national and subregional prevalence of Lm in milk in Africa and identify impacting factors via generalized logistic mixed-effects (GLMEs) and meta-regression modelling. Lm-milk-specific data acquired from primary studies according to standard protocol were fitted using a GLMEs. The GLMEs was subjected to leave-one-study-out-cross-validation (LOSOCV). Factors impacting Lm prevalence in milk were assayed via a 1000-permutation-assisted meta-regression-modelling. The pooled prevalence of Lm in milk in Africa was 4.35% [2.73–6.86] with a prediction interval (PI) of 0.14–59.86% and LOSOCV value of 2.43% [1.62–3.62; PI: 0.32–16.11%]. Western Africa had the highest prevalence [20.13%, 4.13–59.59], then Southern Africa [5.85%, 0.12–75.72], Northern Africa [4.67%, 2.82–7.64], Eastern Africa [1.91%, 0.64–5.55], and there was no record from Central Africa. In term of country, Lm prevalence in milk significantly (p < 0.01) varied from 0.00 to 90.00%. Whereas the Lm prevalence was negligibly different (p = 0.77) by milk type, raw-milk had the highest prevalence [5.26%], followed by fermented-milk [4.76%], boiled-milk [2.90%], pasteurized-milk [1.64%], and powdered-milk [1.58%]. DNA extraction approach did not significantly (p = 0.07) affect Lm prevalence (Boiling [7.82%] versus Kit [7.24%]) as well as Lm detection method (p = 0.10; (ACP [3.64%] vs. CP [8.92%] vs. CS [2.27%] vs. CSP [6.82%]). Though a bivariate/multivariate combination of all tested variables in meta-regression explained 19.68–68.75% (R2) variance in Lm prevalence in milk, N, nation, and subregion singly/robustly accounted for 17.61% (F1;65 = 7.5994; p = 0.005), 63.89% (F14;52 = 4.2028; p = 0.001), and 16.54% (F3;63 = 3.4743; p = 0.026), respectively. In conclusion, it is recommended that adequate sample size should be prioritized in monitoring Lm in milk to prevent spuriously high or low prevalence to ensure robust, plausible, and credible estimate. Also, national efforts/interests and commitments to Lm monitoring should be awaken.

Inactivation of foodborne and other pathogenic bacteria with pyrrolidine based fatty acid amide derivatives

AbstractFoodborne pathogens are a persistent threat to food and consumer safety. To mitigate outbreaks and contamination incited by these pathogens, the development of novel preventative safety controls and biorational inactivation measures are paramount. The objectives of this research were to evaluate the efficacy of pyrrolidine‐based amide derivatives of decanoic (DEPY), lauric (LAPY), myristic (MYPY) and palmitic (PAPY) fatty acids for in‐vitro inhibition and inactivation of various Gram‐positive bacterial strains including Listeria monocytogenes (typically associated with foodborne illness), Bacillus subtilis, and Streptococcus mutans and Streptococcus sobrinus (both normally present in the oral cavity and involved with dental caries). Compared to no treatment (control), significant differences (P &lt; 0.05) in the growth of Listeria strains were seen in‐vitro with increased inhibition at higher amide concentrations (10,000–20,000 ppm). Furthermore, in‐vitro growth inhibition of B. subtilis, S. sobrinus, and S. mutans was also observed with an effectiveness of LAPY&gt;MYPY&gt;PAPY&gt;DEPY. In co‐inoculation assays, LAPY treatment significantly reduced Listeria growth from 1.55 to &gt;5.0 Log CFU/mL when a concentration range of 5 to 250 ppm was applied. Moreover, Listeria populations on pathogen‐inoculated produce were significantly (P &lt; 0.05) reduced from 0.51 to &gt;3.00 Log CFU/g with greater inactivation on carrots compared to alfalfa, soybean, and pistachio. These results demonstrated the potential value of these FA amides against Gram‐positive pathogenic bacteria. Biorational applications of antibacterial FA amides on fresh produce as a postharvest intervention process offers a great potential for enhancement of food safety.

Antimicrobial Activity of Spanish Propolis against Listeria monocytogenes and Other Listeria Strains.

The outbreaks of Listeria associated with food consumption are increasing worldwide concurrently with public concern about the need for natural growth inhibitors. In this context, propolis seems to be a promising bioactive product collected by honeybees, due to its antimicrobial activity against different food pathogens. This study aims to evaluate the efficacy of hydroalcoholic propolis extracts for controlling Listeria under several pH conditions. The physicochemical properties (wax, resins, ashes, impurities), the bioactive compounds (phenolic and flavonoid content), and the antimicrobial activity of 31 propolis samples collected from the half North of Spain were determined. Results showed similar trends in the physicochemical composition and bioactive properties, regardless of the harvesting area. Non-limiting pH conditions (7.04, 6.01, 5.01) in 11 Listeria strains (5 from collection and 6 wild strains from meat products) exhibited MICs (Minimum inhibition concentration) and MBCs (Minimum bactericidal concentration) ranging from 39.09 to 625 μg/mL. The antibacterial activity increased under acidic pH conditions, showing a synergistic effect at pH = 5.01 (p < 0.05). These findings suggest the potential of Spanish propolis as a natural antibacterial inhibitor to control Listeria growth in food products.

Assessment of the relationship between the MLST genetic diversity of Listeria monocytogenes and growth under selective and non-selective conditions

Listeria monocytogenes can grow under stressful conditions and contaminate various food categories. Progresss in DNA sequencing-based identification methods, such as multi-locus sequence typing (MLST) now allow for more accurate characterization of pathogens. L. monocytogenes MLST genetic diversity is reflected by the different prevalence of the “clonal complexes” (CCs) in foods or infections. Better understanding of the growth potentials of L. monocytogenes is essential for quantitative risk assessment and efficient detection across CCs genetic diversity. Using optical density measurements taken with an automated spectrophotometer, we compared the maximal growth rate and lag phase of 39 strains from 13 different CCs and various food origins, in 3 broths mimicking stresful food conditions (8 °C, aw 0.95 and pH5) and in ISO Standard enrichment broths (Half Fraser and Fraser). This is important as growth could influence risk through pathogen multiplication in food. Besides, enrichment problems could lead to a lack of detection of some CCs. Despite small differences highlighting natural intraspecific variability, our results show that growth performances of L. monocytogenes strains under the conditions tested in selective and non-selective broth do not appear to be strongly correlated to CCs and cannot explain higher CC “virulence” or prevalence.

A novel approach for accelerating smear development on bacterial smear-ripened cheeses reduces ripening time and inhibits the growth of Listeria and other unwanted microorganisms on the rind

Bacterial smear-ripened cheeses are commonly contaminated with fungi and the potentially dangerous pathogen Listeria monocytogenes, which compromises food safety and quality. Here, we present new approach for accelerating smear development on these cheeses, while reducing growth of unwanted microorganisms. We grew the smear microorganism Brevibacterium linens in acid whey (AW) supplemented with a by-product of whey protein hydrolysate production (FCH). B. linens grew to a high cell density (10.27 log 10 CFU/mL), and alkalized the AW-FCH medium. We found that the fermented AW-FCH, with its high pH, rapidly killed L. monocytogenes and yeasts. When culture medium was smeared on the cheese surface, the surface pH was rapidly neutralized, and in just 7 days, the cheeses developed a dense orange color and growth of spoilage fungi was inhibited. Summing up, by growing B. linens to high cell density on low-value dairy byproducts, and applying dense suspensions onto cheeses, we can reduce the time needed for establishing the smear. Added benefits are increased food safety and less spoilage, as quick smear development inhibits growth of unwanted microorganisms on the rind. Preliminary tests at a dairy show that flavor development is comparable to traditional bacterial surface-ripened cheeses with far more complex surface microflora.

Growth of food-borne pathogens Listeria and Salmonella and spore-forming Paenibacillus and Bacillus in commercial plant-based milk alternatives

The objective of the present study was to compare the growth of food-pathogens Listeria monocytogenes, Salmonella enterica, food spoilage Bacillus subtilis, an industrial milk product isolate, and spore-forming Paenibacillus in commercially available ultrahigh temperature processed (UHT) bovine milk and non-dairy, plant-based beverages (coconut, almond, cashew) stored at chilled and ambient temperatures (4 °C, 8 °C or 20 °C). Beverage samples were inoculated with a strain cocktail or individual strains of either Listeria or Salmonella, or Paenibacillus or Bacillus, respectively (approximately 1 × 103 CFU/mL). The findings indicate that the bacterial strains used in the study were capable of proliferating in plant-based beverages at higher rates than in bovine milk at 8 °C and 20 °C for Listeria and 20 °C for Salmonella and Paenibacillus, respectively. Bacillus subtilis grew equally fast in bovine milk and plant-based almond drink at 20 °C. No statistically significant difference (p > 0.05) in growth rates between different types of tested beverages was observed at 4 °C and at 8 °C for Listeria and Salmonella cocktails, respectively. These data suggest that plant-based beverages may present a significant risk for listeriosis and salmonellosis and post-opening recommendations should be carefully considered.

Probiotic and Functional Characterization of Pediococcus acidilactici Isolated from Bhaati jaanr, Traditional Fermented Rice Porridge.

Traditional fermented foods are the ideal source of novel probiotic isolates which are known to have significant therapeutic benefits and play a vital role as bioprotective agents. Bhaati jaanr is an ethnic fermented rice beverage popularly consumed in sub-Himalayan regions. The strain UAMS was isolated from Bhaati jaanr based on high butyrate production and evaluated for the potential probiotic characteristics. MALDI-TOF MS and 16s rRNA gene sequencing revealed the identity of strains as Pediococcus acidilactici. The isolated strain exhibited high tolerance to gastric and bile stress, autoaggregation, hydrophobicity, and adherence to colon cells. Antibiotic susceptibility testing results showed the resistance of the isolated strain toward tested common antibiotics and the pathogenic determinants were absent in PCR-based detection. Moreover, the organism was able to inhibit the growth of Listeria, Salmonella, Staphylococcus, and Enterococcus species. The isolate was found to be a high butyrate producer along with other short-chain fatty acids and exhibited an anti-proliferative effect against colon cancer cells HT29 and SW480. Therefore, our study represents Pediococcus acidilactici UAMS as a potent putative probiotic with bioprotective abilities.

Antilisterial action of PLA films with ferulic acid as affected by the method of incorporation

Previous studies demonstrated that polylactic acid (PLA) films with ferulic acid (F) obtained by melt blending did not release the active compound to exert effective antibacterial action. To solve this problem, different strategies to promote the active properties of PLA-F materials have been studied: film processing by casting with F up to 10% w/w, surface loading of thermoprocessed films with F, by adsorption or pulverisation with F solutions, and electrospinning of PLA-F solutions, using different solvent systems, to obtain nanostructured mats. The materials obtained were characterised by their morphological properties and antilisterial activity. F crystallised inside cast films and on the surface loaded PLA films. Electrospun materials exhibited different morphology, depending on the solvent system of the initial solution; fibre mats were obtained with ethyl acetate-DMSO mixtures, whereas bead structures were mainly formed with glacial acetic acid with or without ethyl acetate. No antilisterial activity was observed in cast films regardless of the F concentration, whereas surface loaded films by adsorption or pulverisation inhibited the listeria growth by about 4 Log (CFU/mL). Electrospun materials only inhibited bacterial growth (3 Log CFU) when these were fibre-structured. Therefore, active films of PLA with F could be only obtained when the active was surface anchored or encapsulated in thin fibre mats, with high surface to volume ratio. In this way, the release of the active compound is promoted, avoiding the problem of its limited internal diffusion through the PLA matrix.

Isolation, discrimination, and molecular detection of Listeria species from slaughtered cattle in Namwala District, Zambia

BackgroundThe food industry is increasingly becoming more scrutinized, given the frequency and intensity with which zoonotic diseases are being reported. Pathogen tracking has become more applicable with regards food safety. It is in this regard that the present study was formulated to track Listeria species. in freshly slaughtered cattle carcasses by utilizing standard and molecular biological techniques.MethodsA cross-sectional study design was conducted from March to December 2020 with 200 samples being equally collected in the rainy and dry seasons. A total of 180 and 20 swabs were aseptically collected from carcasses and the environment respectively. Samples were first subjected to pre-enrichment in half-strength Fraser broth followed by enrichment in full strength Fraser broth and subsequent plating on Listeria agar. Listeria growth characteristics were identified up to species level based on their morphological and biochemical characteristics. Further, molecular detection and phylogenetic analysis was conducted. Quantitative proportionate survey data were analyzed using Stata Version 15 software to estimate crude prevalence taking into account complex design at abattoir level. Factors associated with contamination were characterized using logistic regression. Sequences were analyzed using, Genetyyx version 12 and phylogenetic Mega.ResultsOf the 200 samples, 19 were positive for Listeria species identified as L.innocua 14/19 (73.7%) and L. monocytogenes 5/19 (26.3%). All isolates were from freshly slaughtered carcasses, and none from environment. Siginificant differences in contamination levels were observed based on season: rainy season yielded 14 (73.6%) whilst the dry season 5 (26.3%). The L. monocytogenes strains showed a high degree of homogeneity on phylogenetic analysis and clustered based on abattoir. Seasonality was identified as a major determinant influencing contamination based on the final logistic regression model.ConclusionThis study found evidence of L. monocytogenes contamination on traditionally raised beef carcasses across various abattoirs surveyed. The failure to find Listeria contamination on the abattoir environment may to a greater extent intimate cattle carccases as primary sources of contamination. However, a more comprerehnsive study incorporating different geographical regions is needed to conclusively ascertain these present findings.

Listeria prevention

<i>Listeria</i> prevention

Investigation of the influence of plant tissue damage on the attachment of Listeria to fresh salad produce

Vegetables and fruits are an important for a healthy life due to them containing nutritionally important minerals and vitamins. Green salads (spinach, lettuce) are popular convenience consumer products, however evidence is increasing that these ready to eat salads have been identified as a source of foodborne illness. There are many pathogenic bacteria which are transmitted by food that can cause serious disease. One of the most important is Listeria monocytogenesbecause it can cause invasive infections and especially because of its ability to grow at low (food refrigeration) temperatures. The aim of this study is to investigate whether compounds released from damaged fresh salad leave have an effect on Listeria growth and virulence. The results in this report show that Listeria was highly responsive to the salad extracts and that growth and biofilm formation were both increased compared to un-supplemented control cultures. Plant derived chemicals also stimulated Listeria growth in serum-SAPI medium. The results also showed that Listeria treated with salad extract was more virulent in a Galleria mellonella infection model.

A 5-Point Listeria Control Plan: A European Perspective

With an aging population and no reduction in Listeria cases, listeriosis is likely to become even more important in Europe, and all potential food industry control measures should be explored. A Listeria 5-point control plan to manage the occurrence of Listeria in high hygiene food manufacturing areas has been developed and trialed in the United Kingdom and Ireland since 2016; it comprises these points: • Prevent entry of Listeria into high hygiene food manufacturing areas using effective barriers. • Ensure that the high hygiene manufacturing infrastructure (building structure, equipment, and utensils) cannot harbor and/or allow the growth of Listeria (Listeria sources). • Ensure that high hygiene good manufacturing practices limit the cross-contamination vectors that can carry Listeria from sources to product or product- contact surfaces. • Design an effective cleaning and disinfection program that will kill or remove any Listeria that has entered the high hygiene area since the previous cleaning program. • Provide an environmental monitoring and microbiological verification sampling program that monitors and verifies Listeria control procedures. This review suggests that the plan develops a team ethos among factory technical, production, engineering, and hygiene functions and that success has been achieved in reducing the prevalence of Listeria in product and the environment.

Co-Occurrence of L. monocytogenes with Other Bacterial Genera and Bacterial Diversity on Cleaned Conveyor Surfaces in a Swine Slaughterhouse.

Bacterial pathogens, such as Listeria monocytogenes, can show resistance to disinfection and persistence on working surfaces, permitting them to survive and contaminate food products. Persistence—a complex phenomenon involving interactions between many bacteria within a biofilm—is modulated by in situ characteristics. This study aimed to describe, in silico, the microbiota identified in a swine slaughterhouse after sanitation procedures to better understand the presence of L. monocytogenes on these surfaces. Molecular tools for characterization of microbial communities were used to assess the relative contribution of different bacteria resulting from this phenomenon, and the 16S rRNA sequencing method was used on samples from meat conveyor belt surfaces collected on four sampling visits to study the co-occurrence between L. monocytogenes and other bacteria. From the background microbiota, a total of six genera were found to be negatively correlated with Listeria spp., suggesting Listeria growth inhibition, competition, or at least an absence of shared habitats. Based on these results, a complete scenario of interactions of Listeria with components of background microbiota was established. This work contributes to identifying avenues that could prevent the growth and persistence of L. monocytogenes on food-processing surfaces.

A Study of Identification Listeria monocytogenes Bacteria Isolated from Raw Vegetables in Madhya Pradesh, India

The modern lifestyle pronounced changed eating habits around the world, today raw vegetables are used for major cravings but the packaging and storage conditions of this output can favor the growth of bacteria Listeria spp. or LM which is a foodborne pathogen. that’s why it is necessary to check as they are difficult to identify and differentiate solely by biochemical tests and molecular methods. The aim of the present study is to explore identification of LM in various raw vegetables from wet and hypermarkets available in selected Madhya Pradesh districts using the different Biochemical test and 16s rRNA method. A variety of available vegetables (n = 312) consumed in the minimally processed states in Madhya Pradesh have examined ten types of selected raw vegetables for the presence of LM to found information on the presence of these organisms in these raw vegetables. In the years 2019-2020, a total of 147 of the 312 different raw vegetable samples collected tested positive for L. spp. or L. monocytogenes. Our findings demonstrated that the presence of L. spp. in selected vegetable products was generally medium, on average 47.11% in the years studied including Listeria monocytogenes.

Antimicrobial Activity of Ferulic Acid in Indonesian Purple Rice through Toll-like Receptor Signaling

Purple rice is a potential source of ferulic acid, which has antimicrobial properties. However, the inhibitory mechanism of ferulic acid on the growth of bacteria, particularly Salmonella and Listeria, has not been elucidated. This study aimed to determine the bioactivity of ferulic acid from purple rice as an antimicrobial agent against Salmonella typhimurium and Listeria monocytogenes using in vitro and in silico analyses. The antimicrobial activity of a purple rice ferulic acid extract was tested using the agar well diffusion method. Its effect on bacterial cells was observed using scanning electron microscopy. Ferulic acid was confirmed to have antimicrobial properties using in silico software to attenuate the binding of bacterial virulence factors (lipoproteins, lipopolysaccharides, and flagellins) to Toll-like receptors (TLRs) and to prevent interactions with peptidoglycans. The purple rice ferulic acid extract inhibited bacterial growth. The inhibitory effects included induction of a biofilm and shrinkage of S. Typhimurium, as well as osmotic lysis of L. monocytogenes. This activity was supported by the ability of ferulic acid to inhibit the binding of bacterial virulence factors with TLRs and block bacterial peptidoglycans. These findings indicate that the purple rice ferulic acid extract acts as antimicrobial, both directly to bacterial cells and indirectly through TLRs. We conclude that ferulic acid from Indonesian purple rice has a biological function as an antimicrobial agent.

Plant Extracts for the Control of Listeria monocytogenes in Meat Products

The antimicrobial activity of garlic (Allium sativum L.) and onion (Allium cepa L.) plant active extracts was determined against Listeria monocytogenes in two meat products. Samples of sausages “cacciatore” and cooked ham in vacuum-packaged slices were artificially contaminated, and the presence of Listeria was evaluated during the sausages ripening and throughout the shelf-life of the cooked ham. The test carried out on sausages did not show differences among treated and untreated samples. The antagonistic activity of the plant extracts against the pathogen was probably hidden by the competition from the sausages microbial flora and the pH and the water activity (aw) decrease. On the other hand, the plant extracts determined an initial reduction of about 1.00 log cfu/g of the L. monocytogenes viable count in the cooked ham slices contaminated with 103 cfu/g, but the best result was obtained with the contamination of 102 cfu/g of L. monocytogenes. In addition to the pathogen’s initial decrease, we observed an extension of the lag phase and a reduction of the Listeria growth rate. Considering that the presence of L. monocytogenes during the slicing phase of the cooked ham does not exceed 10 cfu/g, the use of plant extracts can lead to complete pathogen elimination.