Enterococci from Raw-Milk Cheeses: Current Knowledge on Safety, Technological, and Probiotic Concerns

Developing Gut-Healthy Strains for Pets: Probiotic Potential and Genomic Insights of Canine-Derived Lactobacillus acidophilus GLA09

Probiotics are widely used to improve pet health and welfare due to their significant biological activity and health benefits. Lactobacillus acidophilus GLA09 was derived from the intestinal tract of healthy beagles. The safety and suitability evaluation of GLA09 was completed through a combination of whole genome sequence and phenotypic analyses, including tests for the inhibition of harmful bacteria, acid resistance, bile salt tolerance, adhesion, and amine-producing substance content. The findings revealed that GLA09 has good gastrointestinal tolerance, inhibits the growth of pathogenic bacteria, and does not produce toxic biogenic amines. The genome of GLA09 comprises one chromosome and one plasmid, with a genome size of 2.10 M and a Guanine + Cytosine content of 38.71%. It encodes a total of 2208 genes, including 10 prophages, and 1 CRISPR sequence. Moreover, 56 carbohydrate-encoding genes were identified in the CAZy database, along with 11 genes for cold and heat stress tolerance, 5 genes for bile salt tolerance, 12 genes for acid tolerance, and 14 predicted antioxidant genes. Furthermore, GLA09 has one lincosamide resistance gene, but there is no risk of transfer. GLA09 harbors a cluster of Helveticin J and Enterolysin A genes linked to antimicrobial activity. Genomic analysis validated the probiotic attributes of GLA09, indicating its potential utility as a significant probiotic in the pet food industry. In summary, L. acidophilus GLA09 has the potential to be used as a probiotic in pet food and can effectively combat intestinal health in pets.

Delving into Roccaverano PDO cheese: A comprehensive examination of microbial diversity and flavour profiles compared to non-PDO cheeses

Roccaverano Protected Designation of Origin (PDO) is a fresh soft cheese produced in Roccaverano area (Italy). This study aimed to evaluate Roccaverano PDO microbiota, together with aromatic profile and sensory analysis to be compared with 15 non-PDO cheeses of the same type. Microbiota was evaluated through shotgun metagenomics sequencing, while GC-MS analysis was conducted to study volatile organic compounds (VOCs) presence and concentration. Sensory analyses were conducted through ONAF (Italian National Organization of Cheese Tasters) evaluation parameters followed by flash profile sensory analysis of selected cheeses. The results demonstrated Lactococcus lactis predominance in both non-PDO and PDO cheeses, while Streptococcus thermophilus was more abundant in non-PDO group. A higher abundance of Kluyveromyces lactis was observed in Roccaverano PDO, which exhibited greater fungal diversity compared to non-PDO cheeses. Metagenome-Assembled Genomes of 26 L. lactis and 19 Leuconostoc mesenteroides showed absence of significant differences in terms of average nucleotide identity and pangenomes partitions. The ONAF sensory evaluation demonstrated a higher average score of Roccaverano PDO group. Flash profile analysis demonstrated that lactic aroma/odour, acid, astringent, vegetal odour, exotic fruit and fermented aroma, hazelnut flavour and sweet were associated with high ONAF scores. The concentration of butanoic acid, 2-methyl-, ethyl ester and butanoic acid, 3-methyl- (sweat, acid, rancid related) were higher in PDO cheeses, while reads related to butanoate metabolism were less abundant compared to non-PDO samples. Several fungal species (included K. lactis) were associated with astringents, acid and chalky flavours. Roccaverano PDO demonstrates unique characteristics even maintaining a certain degree of variability between samples.

Potentially probiotic NPL 1334 strain of Enterococcus durans benefits rats with diet-induced hypercholesterolemia

PURPOSE

To study the potential of a candidate probiotic strain belonging to the Enterococcus durans species in alleviating hypercholesterolemia and improving the microbial milieu of rat gut.

METHODS

A previously isolated and characterized E. durans strain NPL 1334 was further screened in vitro for its bile salt hydrolyzation and cholesterol assimilation ability. An in vivo trial using diet-induced hypercholesterolemic rats was conducted to evaluate the effects of the administered test probiotic strain on the animal's blood biochemical parameters such as total cholesterol (TC), high-density lipopolysaccharides (HDL), low-density lipopolysaccharides (LDL), triglycerides (TG), on body weight, oxidative stress markers, and its impact on intestinal and fecal microbiota as well as a histopathological examination of the test animal's livers.

RESULTS

E. durans strain showed good bile salt hydrolyzing ability and ample cholesterol assimilation in vitro. Probiotic-fed hypercholesterolemic rats showed significantly lowered cholesterol, triglyceride and LDL levels. The body weight of probiotic-fed rats was reduced as compared to the control. E. durans also stimulated the growth of beneficial LAB in the intestine of experimental rats and did not harm the liver of the experimental rats.

CONCLUSION

E. durans can be a natural therapeutic alternative to manage diet-induced hypercholesterolemia and may eventually enhance anti-cholesterolemic therapies.

Antibiotic Resistance in Fermented Foods Chain: Evaluating the Risks of Emergence of Enterococci as an Emerging Pathogen in Raw Milk Cheese

Fermented foods, particularly fermented dairy products, offer significant health benefits but also present serious concerns. Probiotic bacteria, such as lactic acid bacteria (LAB), found in these foods have been strongly linked to the selection and dissemination of antibiotic resistance genes (ARGs). This study aims to examine the potential risks associated with fermented foods, despite their importance in human nutrition, by analyzing the entire production chain from raw material acquisition to storage. Focusing on cheese production as a key fermented food, the study will investigate various aspects, including dairy farm management, milk acquisition, milk handling, and the application of good manufacturing practices (GMP) and good hygiene practices (GHP) in cheese production. The findings of this review highlight that ARGs found in LAB are similar to those observed in hygiene indicator bacteria like E. coli and pathogens like S. aureus. The deliberate use of antibiotics in dairy farms and the incorrect use of disinfectants in cheese factories contribute to the prevalence of antibiotic-resistant bacteria in cheeses. Cheese factories, with their high frequency of horizontal gene transfer, are environments where the microbiological diversity of raw milk can enhance ARG transfer. The interaction between the raw milk microbiota and other environmental microbiotas, facilitated by cross-contamination, increases metabolic communication between bacteria, further promoting ARG transfer. Understanding these bacterial and ARG interactions is crucial to ensure food safety for consumers.

Preparation and characterization of carboxymethylated pullulan/butyric acid-modified chitosan active sustainable bi-layer coatings intended for packaging of cheese slices

Dependence of the food industry on conventional plastic and the generation of enormous amounts of food waste caused by microbiological spoilage have been imposed as inspiration for this work, to develop active sustainable packaging for sliced cheese using the bi-layer design. Pullulan was modified using a green approach to obtain a polyanionic character in the coating formulation. Chitosan, which has a cationic character in an acidic environment, has been modified using a butyric acid to obtain an amphiphilic character. The formed active bi-layer has demonstrated an improved barrier (decreased permeability for moisture vapor 72.2 and 77.7 times) and mechanical properties (increased tensile strength value up to 3.9 and 9.4 times) compared to the monolayer films. A novel approach to microbiological control of sliced cheese has been established, which implies a synergistic effect of Helichrysum italicum essential oil (EO) and corresponding hydrolate (HY) incorporated in separated layers. This design has ensured avoiding surfactants and preserving cheese's sensory properties, prolonging its shelf-life by 50 % at least. Improvements in cheese storage conditions using this packaging lie in the improved barrier, mechanical and antimicrobial properties, the order of lamination, and a good covering of the cheese surface by spraying.

Beyond Harmful: Exploring Biofilm Formation by Enterococci Isolated from Portuguese Traditional Cheeses

This study investigated the biofilm-forming capabilities of Enterococcus isolates from Portuguese traditional cheeses with protected designation of origin (PDO) status, specifically Azeitão and Nisa. Given the absence of added starter cultures in the cheesemaking process, the characteristics of these cheeses are intrinsically linked to the autochthonous microbiota present in the raw materials and the production environment. Our findings demonstrate that all isolates possess biofilm production abilities, which are crucial for their colonization and persistence within cheese factories, thereby maintaining factory-specific microbial heritage. Through an integrated analysis utilizing principal component analysis (PCA), a direct correlation between biofilm formation and cell viability was established. Notably, these results underscore the adaptive capacity of enterococci to survive environmental fluctuations and their role in the unique characteristics of Portuguese traditional cheeses. Overall, this research enhances our understanding of the microbial dynamics in cheese production and highlights the importance of enterococci in preserving cheese quality and heritage.

Cutting-Edge iPSC-Based Approaches in Studying Host-Microbe Interactions in Neuropsychiatric Disorders

Gut microbiota (GM), together with its metabolites (such as SCFA, tryptophan, dopamine, GABA, etc.), plays an important role in the functioning of the central nervous system. Various neurological and psychiatric disorders are associated with changes in the composition of GM and their metabolites, which puts them in the foreground as a potential adjuvant therapy. However, the molecular mechanisms behind this relationship are not clear enough. Therefore, before considering beneficial microbes and/or their metabolites as potential therapeutics for brain disorders, the mechanisms underlying microbiota-host interactions must be identified and characterized in detail. In this review, we summarize the current knowledge of GM alterations observed in prevalent neurological and psychiatric disorders, multiple sclerosis, major depressive disorder, Alzheimer's disease, and autism spectrum disorders, together with experimental evidence of their potential to improve patients' quality of life. We further discuss the main obstacles in the study of GM-host interactions and describe the state-of-the-art solution and trends in this field, namely "culturomics" which enables the culture and identification of novel bacteria that inhabit the human gut, and models of the gut and blood-brain barrier as well as the gut-brain axis based on induced pluripotent stem cells (iPSCs) and iPSC derivatives, thus pursuing a personalized medicine agenda for neuropsychiatric disorders.

Microbiological Evaluation of Two Mexican Artisanal Cheeses: Analysis of Foodborne Pathogenic Bacteria in Cotija Cheese and Bola de Ocosingo Cheese by qPCR

Cotija and Bola de Ocosingo are artisanal ripened cheeses produced in Mexico. Both are made with raw bovine milk from free-grazing cows and with no starter cultures. Unlike culture-based techniques, molecular methods for pathogen detection in food allow a shorter turnaround time, higher detection specificity, and represent a lower microbiological risk for the analyst. In the present investigation, we analyzed 111 cheese samples (95 Cotija and 16 Bola de Ocosingo) by qPCR (TaqMan®) after an enrichment-culture step specific to each foodborne bacterium. The results showed that 100% of the samples were free of DNA from Listeria monocytogenes, Brucella spp., Escherichia coli enterotoxigenic (ETEC), and O157:H7; 9% amplified Salmonella spp. DNA; and 11.7%, Staphylococcus aureus DNA. However, the threshold cycle (Ct) values of the amplified targets ranged between 23 and 30, indicating DNA from non-viable microorganisms. Plate counts supported this assumption. In conclusion, 100% of the cheeses analyzed were safe to consume, and the enrichment step before DNA extraction proved essential to discern between viable and non-viable microorganisms. Hygienic milking, milk handling, cheese manufacturing, and ripening are crucial to achieve an adequate microbiological quality of cheeses made with raw milk.

Potential Probiotic Properties and Complete Genome Analysis of Limosilactobacillus reuteri LRA7 from Dogs

This study aimed to isolate and screen canine-derived probiotics with excellent probiotic properties. Strain characterization was conducted using a combination of in vitro and in vivo probiotic characterization and safety assessments, as well as complete genome analysis. The results showed that Limosilactobacillus reuteri LRA7 exhibited excellent bacteriostatic and antioxidant activities. The survival rate at pH 2.5 was 79.98%, and the viable counts after exposure to gastrointestinal fluid and 0.5% bile salts were 7.77 log CFU/mL and 5.29 log CFU/mL, respectively. The bacterium also exhibited high hydrophobicity, self-coagulation, and high temperature tolerance, was negative for hemolysis, and was sensitive to clindamycin. In vivo studies in mice showed that the serum superoxide dismutase activity level was 53.69 U/mL higher in the MR group of mice compared to that of the control group, the malondialdehyde content was 0.53 nmol/mL lower in the HR group, and the highest jejunal V/C value was 4.11 ± 1.05 in the HR group (p < 0.05). The L. reuteri LRA7 gene is 2.021 megabases in size, contains one chromosome and one plasmid, and is annotated with 1978 functional genes. In conclusion, L. reuteri LRA7 has good probiotic potential and is safe. It can be used as an ideal probiotic candidate strain of canine origin.

Description of Ewiss cheese, a new ewe milk cheese processed by Swiss cheese manufacturing techniques: Microbiological, physicochemical, and sensory aspects

Typically, Swiss-type cheese is made from cow milk. However, in the present work an attempt to expand the sheep supply chain and product offering in this field was made by developing a new type of cheese using Swiss-type cheese technology. The cheese was manufactured under industrial conditions, and fermentations were carried out using freeze-dried commercial starters that are traditionally used in the production of Swiss cheese. Two experimental "Ewiss cheese" (EC) products were produced using raw milk (RM) and pasteurized milk (PM), respectively. Fourteen microbial groups were investigated by plate counts from curd until ripened cheeses. According to microbiological analyses, no statistically significant differences were found between the 2 productions with respect to the group of lactic acid bacteria (LAB). The curds were mainly characterized by mesophilic LAB cocci (7.45 log10 cfu/g in RM-EC and 7.33 log10 cfu/g in PM-EC). However, at the end of the ripening period (9 mo), the cheeses exhibited a higher presence of mesophilic LAB rods. Undesired microbiological groups were found only in the curd of raw milk cheese in the range of 104 to 105 cfu/g, but they were reaching undetectable levels by plate count in the cheese at the end of ripening. The RM-EC and PM-EC were characterized by 76% and 68% of DM, respectively. These cheeses contained 29.30% and 34.36% of protein, and 51.31% and 50.38% of fat, respectively. Textural analysis showed differences in terms of hardness, chewiness, and gumminess between the experimental cheeses and Swiss cheese sold on the market. These differences could be attributed to the higher protein content of ewe milk. The main fatty acids in the cheeses were palmitic acid, myristic acid, oleic acid, and capric acid. Among the organic acids, RM-EC had higher concentrations of lactic acid, whereas PM-EC was higher in propionic acid. The ewe cheeses emitted 46 volatile compounds, including acids, aldehydes, ketones, esters, alcohols, and other compounds. The PM-EC was characterized by the main compounds of Swiss-type cheese: acetic acid, butyric acid, ethyl butyrate, ethyl caproate, propanoic acid, and tetramethylpyrazine. Sensory evaluation showed that the new dairy products were generally appreciated, and PM-EC was the most preferred by the judges. This research has enabled the development of new ewe milk products, which could stimulate the valorization of a sector that has been long neglected and still has a large margin of improvement.

Insight into the Probiogenomic Potential of Enterococcus faecium BGPAS1-3 and Application of a Potent Thermostable Bacteriocin

This study aimed to investigate the probiogenomic features of artisanal bacteriocin-producing Enterococcus faecium BGPAS1-3 and the use of the improved pMALc5HisEk expression vector for overexpressing class II bacteriocins and the application of purified bacteriocin 31 in a milk model as a preservative against L. monocytogenes. The BGPAS1-3 strain was isolated from traditional fresh soft cheese manufactured in households on a small scale in rural locations surrounding Pale Mountain City in Bosnia and Herzegovina. The whole-genome sequencing approach and bioinformatics analyses revealed that the strain BGPAS1-3 was non-pathogenic to humans. The presence of bacteriocin operons suggested the ability of the isolate to suppress the growth of pathogens. Coding regions for three maturated bacteriocins (bacteriocin 31, bacteriocin 32, and enterocin P) produced by BGPAS1-3 were amplified and expressed in Escherichia coli ER2523 using the pMALc5HisEk system. All three bacteriocins were successfully overexpressed and purified after enterokinase cleavage but showed different antimicrobial activity. Bacteriocin 31 showed significantly stronger antimicrobial activity compared with bacteriocin 32. It was the only one that proved to be suitable for use as a food preservative against L. monocytogenes in a milk model.

Occurrence of Enterococci in the Process of Artisanal Cheesemaking and Their Antimicrobial Resistance

Enterococci are a group of microorganisms that have a controversial position from some scientific points of view. The species of the greatest clinical importance are E. faecalis and E. faecium, which are common agents of nosocomial infections. However, enterococci also have important applications in the dairy industry, as they are used as non-starter lactic acid bacteria (NSLAB) in a variety of cheeses, especially artisanal cheeses. The aim of this study was to determine the presence of representatives from the Enterococcus genus using PCR and MALDI-TOF MS methods on samples of raw milk, processing environment swabs, and cheese from four different artisanal dairy plants in Slovakia. Among the 136 isolates of enterococci, 9 species of genus Enterococci (E. faecalis, E. faecium, E. durans, E. devriesi, E. hirae, E. italicus, E. casseliflavus, E. malodoratus, and E. gallinarum) were identified and were tested for their antimicrobial resistance (AMR) to 8 antibiotics (amoxicillin, penicillin, ampicillin, erythromycin, levofloxacin, vancomycin, rifampicin, and tetracycline); most of them were resistant to rifampicin (35.3%), ampicillin (22.8%), and tetracycline (19.9%). A PCR analysis of vanA (4.41%) and tetM (14.71%) revealed that antimicrobial resistance genes were present in not only phenotypic resistant isolates of enterococci but also susceptible isolates. The investigation of antimicrobial resistance in enterococci during the cheesemaking process can be a source of valuable information for public health in the concept of "One Health".

Insight into the Postbiotic Potential of the Autochthonous Bacteriocin-Producing Enterococcus faecium BGZLM1-5 in the Reduction in the Abundance of Listeria monocytogenes ATCC19111 in a Milk Model

This study aimed to explore the probiogenomic characteristics of artisanal bacteriocin-producing Enterococcus faecium BGZLM1-5 and its potential application in reducing Listeria monocytogenes in a milk model. The BGZLM1-5 strain was isolated from raw cow's milk from households in the Zlatar Mountain region. The whole genome sequencing approach and bioinformatics analyses reveal that the strain BGZLM1-5 is non-pathogenic to humans. Bacteriocin-containing supernatant was thermally stable and antimicrobial activity retained 75% of the initial activity compared with that of the control after treatment at 90 °C for 30 min. Antimicrobial activity maintained relative stability at pH 3-11 and retained 62.5% of the initial activity compared with that of the control after treatment at pH 1, 2, and 12. The highest activity of the partially purified bacteriocin was obtained after precipitation at 40% saturation with ammonium sulfate and further purification by mixing with chloroform. Applying 3% and 5% (v/v) of the bacteriocin-containing supernatant and 0.5% (v/v) of the partially purified bacteriocin decreased the viable number of L. monocytogenes ATCC19111 after three days of milk storage by 23.5%, 63.5%, and 58.9%, respectively.

Multidrug Resistance in Enterococci Isolated from Cheese and Capable of Producing Benzalkonium Chloride-Resistant Biofilms

This study aimed to investigate enterococci recovered from eight Portuguese cheeses made with raw ewe's milk, regarding antibiotic resistance, virulence genes, minimum inhibitory concentration (MIC) of benzalkonium chloride (BAC), biofilm formation capacity, and biofilm eradication (MBEC) by BAC. Antimicrobial resistance against seven antibiotics of five groups was evaluated using the disk diffusion method. The presence of the genes that encode resistance to the antibiotics penicillin (blaZ), erythromycin (ermA, ermB, and ermC), vancomycin (vanA and vanB), aminoglycoside (aac(6')-Ie-aph(2″)-Ia), and β-lactam (pbp5) and the genes that encode virulence factors, frsB, cylA, gelE, esp, and agg, were investigated via multiplex PCR. The susceptibility of planktonic cells to BAC was evaluated by the MIC and MBC values of the isolates, using the broth microdilution method. To assess the biofilm-forming ability and resistance of biofilms to BAC, biofilms were produced on stainless steel coupons, followed by exposure to BAC. The results showed a high resistance to the antibiotics vancomycin (87.5%), erythromycin (75%), tetracycline (50%), and penicillin (37.5%). Multidrug resistance was observed in 68.8% of the isolates. Genes encoding the virulence factors FrsB (frsB) and gelatinase E (gelE) were detected in all isolates. The esp and cylA genes were found in 56.3% and 37.5% of the isolates, respectively. All isolates exhibited a biofilm-forming ability, regardless of incubation time and temperature tested. However, after 72 h at 37 °C, E. faecium and E. faecalis biofilms showed significant differences (p ≤ 0.05). Although most isolates (62.5%) were susceptible to BAC (MIC ≤ 10 mg/L), biofilms of the same isolates were, generally, resistant to the higher concentration of BAC (80 mg/mL) tested. This study using Enterococcus isolates from a ready-to-eat food, such as cheese, reveals the high percentages of vancomycin resistance and multidrug resistance, associated with the presence of virulence genes, in isolates also capable of producing biofilms resistant to BAC, an important active ingredient of many disinfectants. These results emphasize the need for effective control measures to ensure the safety and quality of dairy products.

Safety evaluation of enterococci isolated from raw milk and artisanal cheeses made in Slovenia and Serbia

Enterococci represent a significant part of the non-starter LAB microbiota of artisanal cheeses produced mainly from raw milk. Common approaches to safety evaluation of enterococci isolates include assessment of antimicrobial resistance and virulence potential. Hence, a collection of 47 (n = 22, Serbia; n = 25, Slovenia) dairy enterococcal isolates, of which E. faecalis (n = 28), E. faecium (n = 11), E. durans (n = 5), E. casseliflavus (n = 2), and E. gallinarum (n = 1), was analyzed. The susceptibility to 12 antimicrobials was tested using a broth microdilution method, and the presence of the selected antimicrobial resistance and virulence genes was investigated using PCR. Isolates were resistant to tetracycline (TET) (25.5%), erythromycin (ERY) (17.0%), gentamycin and chloramphenicol (CHL) (∼6%). No resistance to ampicillin (AMP), ciprofloxacin (CIP), daptomycin (DAP), linezolid (LZD), teicoplanin (TEI), tigecycline (TGC) and vancomycin (VAN) was detected. Among all the resistance determinants analyzed, ermB gene was detected most frequently. All 10 virulence genes analyzed were detected with a distribution of cpd (72.3%), cob and ccf (70.2%), gelE (68.1%), hyl (59.6%), agg (53.2%) and esp (46.8%). The genes encoding cytolysin (cylA, cylM and cylB) were amplified to a lesser extent (21.3%, 21.3% and 12.8%, respectively). However, due to the limited number of enterococci isolates analyzed in the present study, further studies are still required in order to better document the safety status of dairy enterococci.

Selection and Characterization of Bacteriocinogenic Lactic Acid Bacteria from the Intestine of Gilthead Seabream (Sparus aurata) and Whiting Fish (Merlangius merlangus): Promising Strains for Aquaculture Probiotic and Food Bio-Preservation

This study sought to evaluate the probiotic properties and the food preservation ability of lactic acid bacteria isolates collected from the intestines of wild marine fishes (gilthead seabream (Sparus aurata) (n = 60) and whiting fish (Merlangius merlangus) (n = 40)) from the Mediterranean sea in the area of Mostaganem city, Algeria. Forty-two isolates were identified as: Enterococcus durans (n = 19), Enterococcus faecium (n = 15), Enterococcus faecalis (n = 4), Lactococcus lactis subp. lactis (n = 3), and Lactobacillus plantarum (n = 1). All isolates showed inhibition to at least one indicator strain, especially against Listeria monocytogenes, Staphylococcus aureus, Paenibacillus larvae, Vibrio alginolyticus, Enterococcus faecalis, Bacillus cereus, and Bacillus subtilis. In all collected isolates, PCR analysis of enterocin-encoding genes showed the following genes: entP (n = 21), ent1071A/B (n = 11), entB (n = 8), entL50A/B (n = 7), entAS48 (n = 5), and entX (n = 1). Interestingly, 15 isolates harbored more than one ent gene. Antimicrobial susceptibility, phenotypic virulence, and genes encoding virulence factors were investigated by PCR. Resistance to tetracycline (n = 8: tetL + tetK), erythromycin (n = 7: 5 ermA, 2 msrA, and 1 mef(A/E)), ciprofloxacin (n = 1), gentamicin (n = 1: aac(6')-aph(2″)), and linezolid (n = 1) were observed. Three isolates were gelatinase producers and eight were α-hemolytic. Three E. durans and one E. faecium harbored the hyl gene. Eight isolates showing safety properties (susceptible to clinically relevant antibiotics, free of genes encoding virulence factors) were tested to select probiotic candidates. They showed high tolerance to low pH and bile salt, hydrophobicity power, and co-culture ability. The eight isolates showed important phenotypic and genotypic traits enabling them to be promising probiotic candidates or food bio-conservers and starter cultures.

Current Advances in Cheese Microbiology

Cheese is a complex microbial ecosystem containing microorganisms that are either deliberately added or that enter milk, curd or cheese as contaminants [...].

The Enterococcus secretome inhibits the growth of Mycobacterium tuberculosis complex mycobacteria

Enterococcus mundtii , a commensal intestinal bacterium, was demonstrated to inhibit the growth of some Mycobacterium tuberculosis complex (MTC) species that cause tuberculosis in humans and mammals. To further explore this preliminary observation, we cross-investigated five E. mundtii strains and seven MTC strains representative of four MTC species using a standardized quantitative agar well diffusion assay. All five E. mundtii strains, calibrated at 10 MacFarland, inhibited the growth of all M. tuberculosis strains with various susceptibility profiles, but no inhibition was observed with lower inoculums. Further, eight E. mundtii freeze-dried cell-free culture supernatants (CFCS) inhibited the growth of M. tuberculosis , Mycobacterium africanum, Mycobacterium bovis and Mycobacterium canettii, the most susceptible MTC species (inhibition diameter 25±1 mm), proportionally to CFCS protein concentrations. The data reported here indicate that the E. mundtii secretome inhibited growth of all MTC species of medical interest, which broadens previously reported data. In the gut, the E. mundtii secretome may modulate the expression of tuberculosis, exhibiting an anti-tuberculosis effect, with some protective roles in human and animal health.

Biofilm Formation Capacity and Presence of Virulence Determinants among Enterococcus Species from Milk and Raw Milk Cheeses

Bacterial biofilm is one of the major hazards facing the food industry. Biofilm-forming ability is one of the most important virulence properties of enterococci. The genus Enterococcus includes pathogenic, spoilage, and pro-technological bacteria. The presence of enterococci in milk and dairy products is usually associated with inadequate hygiene practices. The study examined the isolates' capacity for biofilm formation and identification of the genetic determinants of its formation among 85 Enterococcus strains isolated from raw milk (n = 49) and soft-ripened cheeses made from unpasteurized milk (n = 36). E. faecalis and E. faecium were the dominant species. The obtained results showed that 41.4% isolates from milk and 50.0% isolates from cheeses were able to form biofilm. All of the isolates analyzed had at least one of the studied genes. As regards the isolates from raw milk, the most prevalent gene was the gelE (85.6%), followed by the asa1 (66.7%). None of the isolates from cheeses showed the presence of cylA and sprE. The most prevalent gene among the strains from this source was the epbC (94.4%), followed by the gelE (88.9%). In isolates from both sources, the presence of proteins from the Fsr group was noted the least frequently. Nevertheless, results showed that were no significant differences between the biofilm-producing Enterococcus spp. and non-biofilm-producing isolates in term of occurrences of tested virulence genes. The ability to produce a biofilm by enterococci isolated from raw milk or ready-to-eat products emphasizes the need for continuous monitoring of the mechanisms of microbial adhesion.

Causality Verification for the Correlation between the Presence of Nonstarter Bacteria and Flavor Characteristics in Soft-Type Ripened Cheeses

Flavor characteristics of ripened cheese are established by various bacteria, such as lactic acid bacteria, Actinobacteria, and Proteobacteria, which spontaneously develop during the cheese-manufacturing process. We previously revealed the relationship between bacterial microbiota and flavor components in soft-type ripened cheeses by using a multiomics approach that combined metagenomics and metabolomics; however, we could not establish a causal relationship. This study aimed to substantiate the causal nature of the correlations revealed by the multiomics approach by using cheese-ripening tests with single isolate inoculation. The bacterial diversity and composition in surface mold-ripened cheeses from Japan and France varied, depending on the differences between the milks (pasteurized or raw), cheese positions (core or rind), and manufacturers. Although the volatile compounds did not clearly reflect the distinctive characteristics of the cheese samples, nonstarter lactic acid bacteria, Actinobacteria, and Proteobacteria positively correlated with ketones and sulfur compounds, as evidenced by a Spearman's correlation analysis. Cheese-ripening tests conducted after inoculation with single bacterial strains belonging to the above-mentioned taxa confirmed that these bacteria formed volatile compounds, in agreement with the correlations observed. In particular, various flavor compounds, such as acids, esters, ketones, and sulfur compounds, were detected in cheese inoculated with Pseudoalteromonas sp. TS-4-4 strain. These findings provide important insights into the role of nonstarter bacteria in the development of cheese flavor and into the effectiveness of the multiomics approach in screening for bacteria that can improve the quality of cheese products. IMPORTANCE Our previous study revealed that the existence of various bacteria, such as lactic acid bacteria, Actinobacteria, and Proteobacteria, clearly correlated with the abundance of flavor components, such as volatile compounds, in soft-type ripened cheeses via a multiomics approach that used 16S rRNA gene amplicon sequencing and headspace gas chromatography-mass spectrometry. However, this approach only showed correlations derived from statistical analyses rather than causal relationships. Therefore, in the present study, we performed cheese-ripening tests using nonstarter bacteria to substantiate the correlations revealed by the multiomics approach in soft-type ripened cheese. Our results suggest the capability of nonstarter bacteria, such as Proteobacteria, to impart flavor to cheese and the effectiveness of the multiomics approach in screening for microbial isolates that can improve the quality of cheese. Overall, our research provides new insights into the importance of bacteria in cheese production.

Dairy Products: A Potential Source of Multidrug-Resistant Enterococcus faecalis and Enterococcus faecium Strains

This study attempts to present the antimicrobial resistance, virulence and resistance genes of Enterococcus faecalis and Enterococcus faecium isolated from raw goat's and sheep's milk and cheese. Strains were identified by PCR. The dominant species was E. faecalis (77.8%) and was most often isolated from raw goat's milk. The percentage of antimicrobial-resistant E. faecalis isolates was higher than that of E. faecium isolates, the former most frequently resistant to lincomycin (98%), tetracycline (63%) and streptomycin (16%). Fourteen (22.3%) E. faecalis and 2 (11.1%) E. faecium isolates were identified as multidrug-resistant (MDR). All MDR E. faecalis strains also had virulence genes, whereas one of the two E. faecium strains had them. The most prevalent virulence genes in E. faecalis isolates were asa1 (69.8%) and gelE (57.1%). The most prevalent resistance genes found in both bacterial species were tet(M) (43.2%) and vgaA (22.2%). Enterococci from dairy products are confirmed to be a potential source of the spread of antimicrobial resistance, MDR strains, and virulence and resistance genes. This study highlights several aspects of the virulence and pathogenicity of E. faecalis and E. faecium isolated from dairy products-aspects which are indications for their ongoing monitoring.

Determination of antilisterial effect of some microbial isolates from traditional zlatar cheese during the fermentation of soft white cheese

The aim of this study was to select autochthonous lactic acid bacteria (LAB) isolates with antilisterial activity from Zlatar cheese and to evaluate the ability of selected LAB to control Listeria monocytogenes growth during soft white cheese production. The genotype characterization of isolated LAB (n = 93) was done using PCR method by 16S rRNA sequencing. In this way, the following isolates were detected: Lactococcus lactis ssp. lactis (40 isolates), Enterococcus faecalis (30), Lactobacillus plantarum (12), Leuconostoc mesenteroides ssp. mesenteroides (3) Lactobacillus garvieae (3), Lactobacillus curvatus (2), Lactobacillus casei (1), Enterococcus faecium (1) and Staphylococcus hominis (1). Each isolated LAB was tested for bacteriocin-producing ability. It was determined that two LAB isolates had bactericidal properties: Lactococcus lactis ssp. lactis SRB/ZS/094 and Enterococcus faecalis SRB/ZS/090. Semi-purified of enterococcal bacteriocin (enterocin) was isolated using precipitation procedures with ammonium sulphate. Its properties were determined (strength and range of activities). Isolated enterocin and bacteriocin-producing Lactococcus strain showed significant antimicribial activity against Listeria monocytogenes, but still the inhibition activity of Staphylococcus aurues and Escherichia coli was not detected. Based on the obtained laboratory results, in the second phase of the research, the antilisterial effect of bacteriocin isolated from Enterococcus faecalis SRB/ZS/090 and cells Lactococcus lactis ssp. lactis SRB/ZS/094 were determined, that are added as additives in the production of soft white cheese through five variants. Cheese supplemented with enterocin (E2) had the lowest aerobic mesophilic bacteria count, indicating that enterocin (E2) play an important role for bio-preservation.

A Lactic Acid Bacteria Consortium Impacted the Content of Casein-Derived Biopeptides in Dried Fresh Cheese

This study aimed to define a consortium of lactic acid bacteria (LAB) that will bring added value to dried fresh cheese through specific probiotic properties and the synthesis of bioactive peptides (biopeptides). The designed LAB consortium consisted of three Lactobacillus strains: S-layer carrying Levilactobacillus brevis D6, exopolysaccharides producing Limosilactobacillus fermentum D12 and plantaricin expressing Lactiplantibacillus plantarum D13, and one Enterococcus strain, Enterococcus faecium ZGZA7-10. Chosen autochthonous LAB strains exhibited efficient adherence to the Caco-2 cell line and impacted faecal microbiota biodiversity. The cheese produced by the LAB consortium showed better physicochemical, textural and sensory properties than the cheese produced by a commercial starter culture. Liquid chromatography coupled with matrix-assisted laser desorption/ionization-time of flight tandem mass spectrometry (LC-MALDI-TOF/TOF) showed the presence of 18 specific biopeptides in dried fresh cheeses. Their identification and relative quantification was confirmed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) using multiple reaction monitoring (MRM). The results also showed that their synthesis resulted mainly from β-casein and also α-S1 casein degradation by proteolytic activities of the LAB consortium. The designed LAB consortium enhanced the functional value of the final product through impact on biopeptide concentrations and specific probiotic properties.