The application of LAB in various sectors, including in the biotechnical and food industry, in human and veterinary practice, and in health-promoting practices and cosmetics, has been the subject of intensive research across the globe, with a range of traditional and innovative methods currently being explored. The rediscovery of old practices, the establishment of new processes based on the production and application of different metabolites produced by LAB, and the formation of novel perspectives on the fermentation processes initiated by LAB, have become areas of significant interest in recent years. Various antimicrobial peptides, including bacteriocins, have been proposed as alternatives to antibiotics or have been suggested for use as their synergistic “partners”. The application field of probiotics is being widened to encompass new innovative areas that are targeted towards personalized practice, with the aim of improving human health. An increasingly extensive understanding of bioactive peptides has heralded their application in practices that are alternative or complementary to Western medicine. Approaches to bio-preservation require fewer chemical preservatives and are, currently, thoroughly explored in food research. The enrichment and fortification of food products with biologically active metabolites, including vitamins, antimicrobials, and immunomodulators, are only some of the research areas that ought to be explored as options for the application of various LAB in the food industry.
The concepts associated with the beneficial properties and safety of LAB have been, and always need to be, jointly explored. Even if several LAB strains have been applied historically as safe and beneficial cultures, various other representatives of LAB have been documented as human and animal pathogens, as phytopathogens, and as also including strains associated with spoilage and deterioration [1]. LAB represent a universe of varied microorganisms, with all of them characterized as Gram-positive, catalase negative, as possessing a common metabolism and as initiating the formation of a similar end product (lactic acid) as a result of carbohydrate fermentation [2]. As a diverse group of microorganisms, they are adapted to various ecosystems and environmental conditions, and can grow at different temperatures and use a variety of carbon sources [1,2]. They are associated with virtually all living forms, from simple eukaryotic organisms and plant material, to the skin and GIT of vertebrates, insects, mollusks, crustaceans, etc. They may be described as either beneficial or as pathogens, but they always possess a clear ecological role in numerous life cycles [2]. Of particular note are species such as Enterococcus spp., some of which are unmistakably opportunistic pathogens and, when associated with vancomycin resistance, pose a serious health threat to humans and to animals [3]; these pathogens are typically associated with nosocomial infections [3]. Simultaneously, however, LAB also comprise species that play a beneficial role in the production of various plants, dairy and meat fermented food products [4], or even as probiotics [5]. It has been suggested that enterococci are producers of bacteriocins, some of which can be applied in the control of food-borne and hospital-associated (human and veterinary) pathogens [6]. However, before proposing a strain, even one belonging to a species with a history of safe application, its safety properties must be appropriately evaluated; this is a necessary and essential step that must be completed prior to its application in food fermentation, as a probiotic for human and animals, in human and veterinary medicine, or in agricultural practices. The novel tools utilized in the evaluation of the safety of microbial cultures, including DNA-associated experimental approaches, have become routine in the last two decades. Considering this, the validation of safety, both of new microbial and currently applied cultures, is now considered essential. In addition to “classical” PCR-based approaches, whole genome sequencing and the appropriate analysis of the generated data have become routine in the evaluation of the safety profile of microbial cultures [7,8,9].
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