Search Results (42)

Dairy products from unpasteurized milk produced using traditional production methods may contain many groups of microorganisms, including Staphylococcus aureus and Listeria monocytogenes. Therefore, the use of postbiotics as an alternative preservation method may be important for improving the safety of these products. Therefore, the main aim of the research conducted was to isolate and identify lactic acid bacteria and prepare postbiotics from selected strains using four different methods, sterilization, pasteurization, sonication and pascalization, to determine their antibacterial properties. The antilisterial and antistaphylococcal activities of the prepared postbiotics were investigated in vitro and in a fresh cheese model. The obtained results showed that the most effective method of postbiotic preparation was pascalization. Both, the results of the MRS medium and the challenge test confirmed that postbiotics produced through pascalization exhibited antistaphylococcal activity. This study may help identify more effective biopreservation compounds to combat pathogens in food products, particularly in dairy products. Full article

Previous research showed that three strains of lactic acid bacteria (LAB)—Leuconostoc mesenteroides, Lacticaseibacillus paracasei and Loigolactobacillus coryniformis—exhibited in vitro anti-listerial activity. The objectives of the present study was: (1) to determine whether the initial pH of heat-treated reconstituted milk affects the growth of Listeria monocytogenes, in monoculture and coculture with each of the LAB strains; and (2) to compare the capacity of the LAB strains to inhibit L. monocytogenes in the milk model. Monoculture and coculture challenge tests were conducted in milk adjusted to three initial pH levels of 5.5, 6.0, and 6.5. A pH-driven model and a Jameson-effect model were fitted to the growth curves. The former provided more precise estimates than the latter. In monoculture, L. mesenteroides exhibited the fastest development at all initial pH levels whereas, in coculture, this strain more effectively controlled L. monocytogenes by reducing its growth rates. As the initial milk pH increased, the maximum concentration of L. monocytogenes in monoculture and in coculture also increased, although the LAB strains were all able to reduce the pathogen’s maximum concentration. These findings demonstrated that adjusting milk to a more acidic pH before fermentation provides an additional barrier against the development of L. monocytogenes. Full article

Autochthonous enterococci surviving mild thermization of raw milk (RM) before traditional Greek cheese processing may simultaneously comprise safe and virulent thermoduric strains with multiple antibiotic resistances (ARs). Therefore, this study biotyped and then compared the ARs of 60 Enterococcus isolates from two antilisterial sheep milks of native Epirus breeds before (RM) and after (TM) thermization at 65 °C for 30 s; the RM isolates were previously genotyped and evaluated for primary safety traits, namely, hemolytic activity, vanA/vanB, cytolysin, and virulence genes, by molecular methods. Biochemically typical and atypical strains of Enterococcus faecium (six biotypes), E. durans (five biotypes), E. faecalis (two biotypes), and E. hirae (one biotype), which were subdominant to other LAB species in RM (19 isolates), prevailed in TM (41 isolates). E. faecium biotypes 1A, 1D, and 1H included multiple-Ent+ (entA/entB/entP or entA/entB) strains with strong antilisterial CFS activity, whereas E. faecium 1X (entA), E. durans 2A, 2B, 2C, and 2X (entA/entP or entP), E. faecalis 3B, and E. hirae 4A (entA) biotypes displayed direct in vitro antilisterial activity only. Biotypes 1D, 1X, and 2A were selected in TM. All E. faecium/durans isolates were susceptible to vancomycin, but the m-Ent + E. faecium biotype 1A and 1D strains were resistant to penicillin, erythromycin, ciprofloxacin, and ampicillin. In contrast, all biotype 1X isolates were susceptible to all antibiotics tested. All E. faecalis and most E. durans isolates were resistant to penicillin but susceptible to erythromycin and ciprofloxacin. Biotype 2X isolates and one virulent (ace; gelE) E. faecalis isolate from RM were tetracycline-resistant. A sporadic RM isolate of E. hirae that was resistant to penicillin and vancomycin was not retrieved from the counterpart TM, but the inclusion of three vancomycin-resistant isolates from TM in the primary biotype 3B of E. faecalis was a cause for concern. In conclusion, based on the results, antibiotic-susceptible representatives of all strain biotypes of the E. faecium/durans group, as well as antagonistic m-Ent+ E. faecium strains from sheep milk that were susceptible to vancomycin and ampicillin and lacking virulence genes, can be included in safe complex natural starters to be developed for onsite use in traditional Greek hard cheese technologies. Full article

Background/Objectives: Listeria monocytogenes is a high-risk pathogen in the food industry involved in several outbreaks. Bacteriocins are natural-origin antimicrobial peptides or proteins that represent a good alternative to synthetic antimicrobials capable of inhibiting the growth of pathogens. This study aimed to purify and identify bacteriocins from the cell-free supernatant of Enterococcus lactis-67, which exhibits antagonistic activity against L. monocytogenes. Methods: Protein purification was performed by precipitation with ammonium sulfate, dialysis, and fast protein liquid chromatography. Active protein fractions were analyzed by SDS-PAGE and identified by mass spectrometry. Results: In addition to enterocins A and B, a novel 47 kDa bacteriocin with LysM and NlpC/P60 domains, on the N- and C-terminal regions, respectively, was identified. This enterocin has not been described for Enterococcus before. Conclusions: This study contributes to the identification of new natural and effective strategies for ensuring food safety. Full article

The production of fermented sausages from poultry meat using traditional technologies and natural maturation conditions is a major challenge. The aim of this study was to identify indigenous microbiota with antilisterial activity from an innovative, additive-free, traditionally fermented chicken sausage. Isolates (n = 88) of lactic acid bacteria (LAB) were collected during maturation and subjected to MALDI-TOF mass spectrometry identification. The capacity to combat Listeria was screened against five strains using the agar well diffusion method in 63 selected LAB isolates. MALDI-TOF mass spectrometry identified four different LAB genera, namely Enterococcus, Lactococcus, Leuconostoc and Lactobacillus, the proportions of which differed significantly during the production phases (p < 0.001). Enterococcus faecalis was the most prevalent LAB species in the initial sausage dough. The presence of lactococci (Lactococcus lactis) and enterococci was detected during the 14- and 30-day ripening period and was gradually displaced by leuconostocs and lactobacilli. Lactobacilli appeared to be abundant during the central and late maturation phases, and consisted of only two species—Latilactobacillus sakei and Latilactobacillus curvatus. In total, 38 LAB isolates (60%) showed antilisterial activity toward at least one Listeria indicator strain. The proportions of antilisterial LAB differed significantly during sausage maturation. Inhibitory activity against all indicator Listeria was detected in the neutralized cell-free supernatants of five strains of Enterococcus faecalis, two L. sakei strains and one Leuconostoc mesenteroides strain. The antilisterial activity observed in the indigenous LAB revealed the possible role of L. sakei as a bioprotective culture, as well as the role of Ln. mesenteroides and E. faecalis as bacteriocin producers, for practical applications. Full article

Listeriosis is a disease associated with the consumption of food contaminated with Listeria monocytogenes. Probiotic lactic acid bacteria (LAB) or their postbiotics have been of interest for their anti-listerial effect. This study focused on isolating LAB from artisanal cheeses and characterizing their potential as probiotics. Twelve LAB isolates exhibiting typical LAB traits were evaluated for their ability to survive in simulated gastric juice, hydrolyze bile salts, auto-aggregate, hydrophobicity, and antagonistic activity against L. monocytogenes. The four most promising LAB strains demonstrated anti-listerial probiotic potential and were identified as Latilactobacillus (Lat.) curvatus SC076 and Lactiplantibacillus (Lact.) paraplantarum SC291, SC093, and SC425. The antimicrobial activity of these strains was mainly attributed to bacteriocin-like substances and organic acids. While three Lact. paraplantarum strains were resistant to ampicillin, Lat. curvatus was sensitive to all tested antibiotics. All selected strains exhibited no hemolytic, gelatinase, and lecithinase activity. Exposure to LAB supernatants resulted in a significant reduction in the adhesion and intracellular count of L. monocytogenes in Caco-2 cells, with Lat. curvatus SC076 showing the most significant effect. Based on its probiotic characteristics, Lat. curvatus SC076 is a promising candidate for functional foods, pending further in vivo studies to assess its potential in the food industry. Full article

Licorice roots are a rich source of bioactive compounds with multiple biological activities. The objective of this study was to evaluate the inhibitory effects of licorice root extract against a range of Listeria strains. In addition, the correlation of its phytochemical composition with antimicrobial properties was also investigated. Thus, the bacteriostatic and bactericidal effects of licorice root extract on seven Listeria monocytogenes strains, L. grayi, L. seeligeri, and L. ivanovii were determined. The minimum inhibitory and bactericidal concentrations ranged from 31.3 to 62.5 µg mL⁻¹ and from 62.5 to 250 µg mL⁻¹, respectively. The phytochemical composition of the extract was also analyzed using advanced LC-DAD- qTOF-MS; it is composed of fifty-one compounds belonging to different subgroups of flavonoids and triterpenoids. Subsequently, the anti-Listeria potency of the most abundant phytochemicals was determined using the AntiBac-Pred web tool. In silico calculation showed that liquiritin-apioside and licorice glycoside C1/C2 were strong growth inhibitors of L. monocytogenes, as their potency was comparable to well-known antibiotic substances. Overall, the present study demonstrates the potent antimicrobial effect of licorice root extract and reveals its active phytochemicals. Full article

Listeria monocytogenes (LM) is a frequent post-process contaminant in meat products. This study aimed to investigate the antilisterial effectiveness of post-process antimicrobial treatments employing olive mill wastewater polyphenolic extract (PE) in commercially manufactured frankfurters. Frankfurters were inoculated on the surface with a three-strain LM mixture (~10² CFU/g), treated on the surface with PE in a 2-fold series of concentrations (PM, 2PM, 4PM) and a control group (CTR) of PE-untreated samples. Then, the frankfurters were vacuum-packed and stored at 4 °C for 28 days. Samples were examined on days 0, 7, 14, 21, and 28 for LM count, in silico growth modeling, and impacts on pH, water activity (a_w), and sensory characteristics. From T(time) 7, the PE treatment showed a significant effect on LM growth, registering maximum Δ values between CTR and 4PM of 3.19, 4.86, 4.59, 4.39 at T7, T14, T21, T28, respectively. Minimum effect was attributable to PM treatment with Δ values (CTR versus PM) of 2.07, 2.52, 1.14, 0.65 at T7, T14, T21, T28, respectively. No significant changes occurred in pH (average 6 at T0 and 5.9 at T28), a_w (average 0.978 at T0 and 0.968 at T28), nor in sensory profile (p > 0.05). These findings suggest that PE is an effective natural antimicrobial, offering a promising approach to enhancing food safety and extending shelf life in meat products. Full article

In recent years, the awareness of healthier lifestyles among consumers has driven to an increased interest in more natural, nutritious, and low-processed foods. Ferulic acid, one of the most abundant phenolic acids in plants, has demonstrated a wide spectrum of antimicrobial activities and a range of biomedical effects, including antioxidant, antiallergic, hepatoprotective, anticarcinogenic, anti-inflammatory, and antithrombotic, among others. The objective of this work was to study the antilisterial effect of ferulic acid (FA, 1500 mg/L) on fresh, ready-to-eat orange (FOJ) and apple (FAJ) juices and evaluate its effect on product quality. The results showed that FA reduced the Listeria monocytogenes population after 9 days of storage at 4 °C, but no effect on the indigenous microbiota was observed. The titratable acidity and color significantly changed. The antioxidant capacity and total phenolic content significantly increased with the addition of FA, being at least two times greater in fortified juices. FAJ and FOJ containing FA were scored lower (6.8 and 5.7 on a 9-point hedonic scale, respectively) than their respective controls. Overall, our results demonstrated that FA treatment could be a useful strategy to maintain the safety of fresh apple and orange juices and increase the antioxidant activity and phenolic content. The potential industrial applications and health benefits of the fortification of fruit juices with FA should be further explored. Full article

Listeria monocytogenes is a foodborne pathogen that represents a serious concern for ready-to-eat (RTE) meat products due to its persistence in production facilities. Among the different strategies for the control of this pathogen, the use of antimicrobial peptides derived from food by-products, such as slaughterhouse blood proteins, has emerged as a promising biocontrol strategy. This study evaluated for the first time the use of peptic hydrolysates of porcine hemoglobin as a biocontrol strategy of L. monocytogenes in RTE pork cooked ham. Pure porcine hemoglobin (Hb-P) and porcine cruor (P-Cru) were hydrolyzed using pepsin at different temperatures (37 °C for Hb-P and 23 °C for P-Cru) for 3 h. Then, the hydrolysates were characterized in terms of their degree of hydrolysis (DH), peptide population, color, and antimicrobial activity (in vitro and in situ) against three different serotypes of L. monocytogenes. Reducing the hydrolysis temperature of P-Cru by 14 °C resulted in a 2 percentage unit decrease in DH and some differences in the peptide composition. Nevertheless, the antimicrobial activity (in situ) was not significantly impacted, decreasing the viable count of L. monocytogenes by ~1-log and retarding their growth for 21 days at 4 °C. Although the color of the product was visibly altered, leading to more saturated reddish and yellowish tones and reduced brightness, the discoloration of the hydrolysates can be addressed. This biopreservation approach holds promise for other meat products and contributes to the circular economy concept of the meat industry by valorizing slaughterhouse blood and producing new antilisterial compounds. Full article

Listeria monocytogenes, the causative agent of listeriosis, is a relevant pathogen in dry fermented sausages (DFSs), and the application of antilisterial starter cultures is an effective intervention strategy to control the pathogen during DFS production. The effect of factors in relation to DFS formulation and production, NaCl (0–40 g/L), Mn (0.08–0.32 g/L), glucose (0–40 g/L) and temperature (3–37 °C), on the behaviour of L. monocytogenes when cocultured with Latilactobacillus sakei 23K (non-bacteriocinogenic) and CTC494 (bacteriocinogenic) strains was studied through a central composite design in meat simulation media. L. sakei and L. monocytogenes counts, pH, lactic acid production and bacteriocin activity were determined in mono and coculture. The pH decrease and lactic acid production were highly influenced by glucose, while production of sakacin K by L. sakei CTC494 was observed at moderate (10 and 20 °C), but not at the lowest (3 °C) and highest (37 °C), temperatures. Coculture growth had no effect on the acidification and bacteriocin production but inhibited and inactivated L. monocytogenes when L. sakei 23K entered the early stationary phase and when L. sakei CTC494 produced sakacin K. Optimal conditions for achieving a 5-log units reduction of L. monocytogenes were at 20 °C, 20 g/L of NaCl, 0.20 g/L of Mn and 40 g/L of glucose, those highlighting the importance of considering product formulation and fermentation conditions for bioprotective starter cultures application. Full article

Among the foodborne illnesses, listeriosis has the third highest case mortality rate (20–30% or higher). Emerging drug-resistant strains of Listeria monocytogenes, a causative bacterium of listeriosis, exacerbate the seriousness of this public health concern. Novel anti-Listerial compounds are therefore needed to combat this challenge. In recent years, marine actinobacteria have come to be regarded as a promising source of novel antimicrobials. Hence, our aim was to provide a narrative of the available literature and discuss trends regarding bioprospecting marine actinobacteria for new anti-Listerial compounds. Four databases were searched for the review: Academic Search Ultimate, Google Scholar, ScienceDirect, and South African Thesis and Dissertations. The search was restricted to peer-reviewed full-text manuscripts that discussed marine actinobacteria as a source of antimicrobials and were written in English from 1990 to December 2023. In total, for the past three decades (1990–December 2023), only 23 compounds from marine actinobacteria have been tested for their anti-Listerial potential. Out of the 23 reported compounds, only 2-allyoxyphenol, adipostatins E–G, 4-bromophenol, and ansamycins (seco-geldanamycin B, 4.5-dihydro-17-O-demethylgeldanamycin, and seco-geldanamycin) have been found to possess anti-Listerial activity. Thus, our literature survey reveals the scarcity of published assays testing the anti-Listerial capacity of bioactive compounds sourced from marine actinobacteria during this period. Full article

The antimicrobial activity of Origanum vulgare var. hirtum (O) and Coridothymus capitatus (C) essential oils (EOs) and hydrolates (HYs) of the same botanical species was evaluated on sixteen L. monocytogenes strains from food and clinical origins. The antimicrobial activity was assessed by Minimum Inhibitory Concentration (MIC) determination, viable cell enumeration over time up to 60 min, and evaluation of the cellular damage through Confocal Laser Scanning Microscope (CLSM) analysis. EOs exhibited antimicrobial activity with MIC values ranging from 0.3125 to 10 µL/mL. In contrast, HYs demonstrated antimicrobial effectiveness at higher concentrations (125–500 µL/mL). The effect of HYs was rapid after the contact with the cells, and the cell count reduction over 60 min of HY treatment was about 1.2–1.7 Log CFU/mL. L. monocytogenes cells were stressed by HY treatment, and red cell aggregates were revealed through CLSM observation. Moreover, the combinations of EOs and HYs had an additive antilisterial effect in most cases and allowed the concentration of use to be reduced, while maintaining or improving the antimicrobial effectiveness. The combined use of EOs and HYs can offer novel opportunities for applications, thereby enhancing the antimicrobial effectiveness and diminishing the concentration of use. This provides the added benefit of reducing toxicity and mitigating any undesirable sensory effects. Full article

Listeria monocytogenes is a foodborne pathogen that causes listeriosis, a group of human illnesses that appear more frequently in countries with better-developed food supply systems. This review discusses the efficacy of actual biocontrol methods combined with the main types of food involved in illnesses. Comments on bacteriophages, lactic acid bacteria, bacteriocins, essential oils, and endolysins and derivatives, as main biological antilisterial agents, are made bearing in mind that, using them, food processors can intervene to protect consumers. Both commercially available antilisterial products and solutions presented in scientific papers for mitigating the risk of contamination are emphasized. Potential combinations between different types of antilisterial agents are highlighted for their synergic effects (bacteriocins and essential oils, phages and bacteriocins, lactic acid bacteria with natural or synthetic preservatives, etc.). The possibility to use various antilisterial biological agents in active packaging is also presented to reveal the diversity of means that food processors may adopt to assure the safety of their products. Integrating biocontrol solutions into food processing practices can proactively prevent outbreaks and reduce the occurrences of L. monocytogenes-related illnesses. Full article

Listeria monocytogenes is a foodborne pathogen that contaminates food-processing environments and persists within biofilms on equipment, thus reaching final products by cross-contamination. With the growing demand for clean-label products, the search for natural antimicrobials as biopreservants, such as bacteriocins, has shown promising potential. In this context, this study aimed to evaluate the anti-listerial action of bacteriocins produced by Enterococcus lactis LBM BT2 in an alternative medium containing sugarcane molasses (SCM). Molecular analyses were carried out to characterize the strain, including the presence of bacteriocin-related genes. In the kinetic study on SCM medium E. lactis, LBM BT2 showed biomass and bacteriocin productions similar to those observed on a sucrose-based medium (control), highlighting the potential of the sugarcane molasses as a low-cost substrate. Stability tests revealed that the molecule remained active in wide ranges of pH (4–10) and temperature (60–100 °C). Furthermore, the proteolytic treatment reduced the biomolecule’s antimicrobial activity, highlighting its proteinaceous nature. After primary purification by salting out and tangential flow filtration, the bacteriocin-like inhibitory substance (BLIS) showed bacteriostatic activity on suspended L. monocytogenes cells and against biofilm formation at a concentration of 0.625 mg/mL. These results demonstrate the potential of the produced BLIS as a biopreservative in the food industry. Full article