The efficacy of individual and combined commercial protective cultures against Listeria monocytogenes, Salmonella, O157 and non-O157 shiga toxin-producing Escherichia coli in growth medium and raw milk

Searching for antibiotic-susceptible bioprotective lactic acid bacteria to control dangerous biological agents in artisanal cheese

Minas artisanal cheese (MAC) samples (n = 59) from 16 municipalities across five traditional MAC-producing regions in Brazil were used to prospect antibiotic-susceptible protective lactic acid bacteria (LAB) against three pathogenic bacteria found in the MAC. From 291 LAB isolates, 84 genetically diverse strains were selected via rep-PCR. MALDI-TOF identification revealed multiple species, predominantly Enterococcus faecalis (n = 37), Enterococcus faecium (n = 21), Lactiplantibacillus plantarum (n = 5) and Lacticaseibacillus rhamnosus (n = 3). The antagonistic activity of these strains was evaluated against Enterococcus faecalis ATCC 29212, Listeria monocytogenes ATCC 5779, and Escherichia coli O157:H7 using spot-on-lawn assays. Several strains showed strong inhibitory effects against E. coli and L. monocytogenes, with halo/colony ratios reaching 4.86 and 4.47, respectively. No antimicrobial peptide producing strain was observed. Antibiotic susceptibility was tested against nine antibiotics, and five strains were susceptible to all antibiotics, while 53 strains were susceptible to 5-8 antibiotics. However, five strains were resistant to all antibiotics, showing the highest resistance to gentamicin (66.7%), cotrimoxazole (58.3%), and streptomycin (57.2%). Resistance genes (aacA-aphD, ermA/B, tetM/O/K/L/S, blaZ, and vanA/B) were screened, and 40 strains harbored at least one gene. Taken together, these results revealed three antibiotic-susceptible bioprotective lactobacilli (L. rhamnosus 52, L. plantarum 177, and L. plantarum 272G) as superior strains, whose efficacy in eliminating E. coli O157 and Listeria monocytogenes in the milk matrix between 7- and 21-days post-inoculation was confirmed. These findings confirm the potential of these autochthonous lactobacilli to improve the safety of dairy, paving the way for their applications in product development in future projects.

Growth of methicillin-resistant Staphylococcus aureus during raw milk soft cheese-production and the inhibitory effect of starter cultures

The consumption of raw milk or raw milk products might be a potential risk factor for the transmission of methicillin-resistant Staphylococcus aureus (MRSA). Therefore, we studied MRSA growth during raw milk soft cheese-production. Furthermore, we investigated the inhibitory effect of four starter cultures (Lactococcus lactis, Lacticaseibacillus rhamnosus, Lactiplantibacillus plantarum, Lactobacillus helveticus) on the growth of MRSA in a spot-agar-assay and in raw milk co-culture following a cheesemaking temperature profile. During the initial phases of raw milk cheese-production, MRSA counts increased by 2 log units. In the ripening phase, MRSA counts only dropped slightly and remained high up to the end of the storage. Comparable MRSA counts were found in the rind and core and strain-specific differences in survival were observed. In the spot-agar-assay, all four starter cultures showed strong or intermediate inhibition of MRSA growth. In contrast, in raw milk, only Lactococcus lactis strongly inhibited MRSA, whereas all other starter cultures only had minor inhibitory effects on MRSA growth. Our results indicate that MRSA follow a similar growth pattern as described for other S. aureus during raw milk soft cheese-production and illustrate the potential use of appropriate starter cultures to inhibit MRSA growth during the production of raw milk cheese.

Comparison of Activity of Commercial Protective Cultures and Thermophilic Lactic Acid Bacteria against Listeria monocytogenes: A New Perspective to Improve the Safety of Sardinian PDO Cheeses

Listeria monocytogenes contamination that occurs during and post-processing of dairy products is a serious concern for consumers, and bioprotective cultures can be applied to control the growth of the pathogen in sheep milk cheeses. However, to respect specifications provided for protected designation of origin (PDO) cheeses, only autochthonous microorganisms can be used as bioprotective cultures in these products. This in vitro study aimed to evaluate thermophilic lactic acid bacteria (LAB) isolated from sheep milk as bio-preservative agents to control L. monocytogenes growth in PDO cheese. Results were compared with those obtained with a commercial protective culture (cPC) composed of a Lactiplantibacillus plantarum bacteriocin producer designed to inhibit L. monocytogenes growth in cheese. The in vitro antilisterial activities of n.74 autochthonous LAB and a cPC were tested against 51 L. monocytogenes strains using an agar well diffusion assay. In addition, 16S rRNA sequencing of LAB isolates with antilisterial activity was conducted and strains of Lactobacillus helveticus, Lactobacillus delbrueckii subsp. indicus, Lactobacillus delbrueckii subsp. sunkii, Lactobacillus delbrueckii subsp. lactis and Enterococcus faecalis were identified. In this study, 33.6% (74/220) bacterial strains isolated from milk had characteristics compatible with thermophilic LAB, of which 17.6% (13/74) had in vitro antilisterial activity. These results demonstrate that raw sheep milk can be considered an important source of autochthonous thermophilic LAB that can be employed as protective cultures during the manufacturing of Sardinian PDO cheeses to improve their food safety. The use of bioprotective cultures should be seen as an additional procedure useful to improve cheese safety along with the correct application of good hygienic practices during manufacturing and the post-processing stages.

Strategies for the Development of Bioprotective Cultures in Food Preservation

Consumers worldwide are increasingly demanding food with fewer ingredients, preferably without chemical additives. The trend called "Clean Label" has stimulated the development and commercialization of new types of bioprotective bacterial cultures. These bacteria are not considered new, and several cultures have been available on the market. Additionally, new bioprotective bacteria are being identified to service the clean label trend, extend the shelf life, and, mainly, improve the food safety of food. In this context, the lactic acid bacteria (LAB) have been extensively prospected as a bioprotective culture, as they have a long history in food production and their antimicrobial activity against spoilage and pathogenic microorganisms is well established. However, to make LAB cultures available in the market is not that easy, the strains should be characterized phenotypically and genotypically, and studies of safety and technological application are necessary to validate their bioprotection performance. Thus, this review presents information on the bioprotection mechanisms developed by LAB in foods and describes the main strategies used to identify and characterize bioprotective LAB with potential application in the food industry.

Active Composite Packaging Reinforced with Nisin-Loaded Nano-Vesicles for Extended Shelf Life of Chicken Breast Filets and Cheese Slices

To meet the demands for more effective and ecofriendly food packaging strategies, the potential of nisin-loaded rhamnolipid functionalized nanofillers (rhamnosomes) has been explored after embedding in hydroxypropyl-methylcellulose (HPMC) and κ-carrageenan (κ-CR)-based packaging films. It was observed that intrinsically active rhamnosomes based nanofillers greatly improved the mechanical and optical properties of nano-active packaging (NAP) films. Incorporation of rhamnosomes resulted in higher tensile strength (5.16 ± 0.06 MPa), Young’s modulus (2777 ± 0.77 MPa), and elongation (2.58 ± 0.03%) for NAP than active packaging containing free nisin (2.96 ± 0.03 MPa, 1107 ± 0.67 MPa, 1.48 ± 0.06%, respectively). NAP demonstrated a homogenous distribution of nanofillers in the biopolymer matrix as elucidated by scanning electron microscopy (SEM). Thermogravimetric analysis (TGA) confirmed that NAP prepared with nisin-loaded rhamnosomes was thermally stable even above 200 °C. Differential scanning calorimetry (DSC) analyses revealed that addition of nisin in nanofillers resulted in a slight increase in Tg (108.40 °C), indicating thermal stability of NAP. Fourier transform infrared spectroscopy (FTIR) revealed slight shift in all characteristic bands of nano-active packaging, which indicated the embedding of rhamnosomes inside the polymer network without any chemical interaction. Finally, when tested on chicken breast filets and cheese slices under refrigerated storage conditions, NAP demonstrated broad-spectrum antimicrobial activity (up to 4.5 log unit reduction) and inhibited the growth of Listeria monocytogenes, Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli. These results suggest that HPMC and κ-CR-based NAP containing functionalized nanofillers can serve as an innovative packaging material for the food industry to improve the safety, quality, and shelf-life of dairy and meat products.

Lactiplantibacillus plantarum subsp. plantarum and Fructooligosaccharides Combination Inhibits the Growth, Adhesion, Invasion, and Virulence of Listeria monocytogenes

Listeria monocytogenes is a foodborne pathogen responsible for many food outbreaks worldwide. This study aimed to investigate the single and combined effect of fructooligosaccharides (FOS) and Lactiplantibacillus plantarum subsp. plantarum CICC 6257 (L. plantarum) on the growth, adhesion, invasion, and virulence of gene expressions of Listeria monocytogenes 19112 serotype 4b (L. monocytogenes). Results showed that L. plantarum combined with 2% and 4% (w/v) FOS significantly (p < 0.05) inhibited the growth of L. monocytogenes (3-3.5 log10 CFU/mL reduction) at the incubation temperature of 10 °C and 25 °C. Under the same combination condition, the invasion rates of L. monocytogenes to Caco-2 and BeWo cells were reduced more than 90% compared to the result of the untreated group. After L. plantarum was combined with the 2% and 4% (w/v) FOS treatment, the gene expression of actin-based motility, sigma factor, internalin A, internalin B, positive regulatory factor A, and listeriolysin O significantly (p < 0.05) were reduced over 91%, 77%, 92%, 89%, 79%, and 79% compared to the result of the untreated group, respectively. The inhibition level of the L. plantarum and FOS combination against L. monocytogenes was higher than that of FOS or L. plantarum alone. Overall, these results indicated that the L. plantarum and FOS combination might be an effective formula against L. monocytogenes.

Probiotic potential of commercial dairy-associated protective cultures: In vitro and in vivo protection against Listeria monocytogenes infection

Protective bacterial cultures (PCs) are commercially available to producers to control undesirable microbes in foods, including foodborne pathogens such as Listeria monocytogenes. They are generally recognized as safe for consumption and many are capable of producing bacteriocins. Yet their potential to act as probiotics and confer a health benefit on the host is not known. This study investigated the ability of three commercial PCs to survive human gastrointestinal conditions and exert anti-infective properties against L. monocytogenes. Counts of two PCs of Lactiplantibacillus plantarum remained unchanged after exposure to simulated gastrointestinal conditions, whereas counts of the PC Lactococcus lactis subsp. lactis were reduced by 5.3 log CFU/mL. Cultures of Lactiplantibacillus plantarum and Lactococcus lactis subsp. lactis adhered to human Caco-2 epithelial cells at ∼ 6 log CFU/mL. This pretreatment reduced subsequent L. monocytogenes adhesion and invasion by 1-1.6 log CFU/mL and 3.8-4.9 log CFU/mL, respectively, compared to control. L. monocytogenes-induced cytotoxicity was also reduced from 29.1% in untreated monolayers to ∼ 8% in those treated with PCs. Pretreatment of Caco-2 monolayers with Lactococcus lactis subsp. lactis and one PC of Lactiplantibacillus plantarum reduced L. monocytogenes translocation by ≥ 1.2 log CFU/mL compared to control (≥ 94.5% inhibition). All PCs significantly reduced Dextran^FITC permeability through Caco-2 monolayers to approximately half that of control. Pretreatment with PCs also reduced L. monocytogenes-induced mortality in Caenorhabditis elegans. These findings demonstrate the potential for commercially produced PCs to exert probiotic effects in the host through protection against L. monocytogenes infection, thus providing an additional benefit to food safety beyond inhibiting pathogen growth, survival, and virulence in foods.

The forgotten role of food cultures

Fermentation is one of if not the oldest food processing technique, yet it is still an emerging field when it comes to its numerous mechanisms of action and potential applications. The effect of microbial activity on the taste, bioavailability and preservation of the nutrients and the different food matrices has been deciphered by the insights of molecular microbiology. Among those roles of fermentation in the food chain, biopreservation remains the one most debated. Presumably because it has been underestimated for quite a while, and only considered - based on a food safety and technological approach - from the toxicological and chemical perspective. Biopreservation is not considered as a traditional use, where it has been by design - but forgotten - as the initial goal of fermentation. The 'modern' use of biopreservation is also slightly different from the traditional use, due mainly to changes in cooling of food and other ways of preservation, Extending shelf life is considered to be one of the properties of food additives, classifying - from our perspective - biopreservation wrongly and forgetting the role of fermentation and food cultures. The present review will summarize the current approaches of fermentation as a way to preserve and protect the food, considering the different way in which food cultures and this application could help tackle food waste as an additional control measure to ensure the safety of the food.

The effect of protective cultures on Staphylococcus aureus growth and enterotoxin production

Staphylococcus aureus is the causative agent of staphylococcal food poisoning and is a common contaminant in milk. Despite efforts to control S. aureus, recalls and outbreaks continue to occur, highlighting the need for additional interventions. This study determined the potential for protective cultures (PC) that are commercially available to producers to control S. aureus growth in raw milk and attenuate virulence by impeding staphylococcal enterotoxin (SE) production in raw milk and laboratory medium. Cultures of Hafnia alvei and Lactococcus lactis effectively inhibited S. aureus growth in raw milk to counts ~5 log CFU/mL lower than control when cocultured following a cheesemaking time and temperature profile; two cultures of Lactobacillus plantarum inhibited growth to ~1.5 log CFU/mL less than control. Cocultures of S. aureus with Lc. lactis, H. alvei and Lb. plantarum in raw milk reduced SE levels by 24.9%, 62.4%, and 76%, respectively. Lc. lactis also decreased SE production in raw milk in the absence of PC-mediated growth inhibition. Significant reductions in SE production in the absence of pathogen growth inhibition were also achieved in laboratory medium. Together, these results demonstrate the potential for PCs to inhibit S. aureus growth and impede SE production in the absence of growth inhibition.