Enterococcus is an important genus belonging to the lactic acid bacteria, generally recognized as safe in food production, and shows favorable metabolic activities contributing to the distinctive taste and flavor of certain food products. Some enterococci strains produce bacteriocins which can vary according to their antimicrobial spectrum, mode of action, molecular mass, thermostability, and pH range of activity. As enterococci are commonly present in many food systems and their technological and probiotic properties are widely recognized, they could be good candidates for potential application of bacteriocin-mediated antagonism against spoilage bacteria and food-borne pathogens. Some enterococci strains are used as probiotics for the maintenance of normal intestinal microbiota, stimulation of the immune system, and improvement of the nutritional value of foods/feeds in humans and animals.

In recent years, there has been a change in the notion that the use of enterococci by the food or pharmaceutical industry is harmless and beneficial because of the alarming increase of their incidence in nosocomial infections, in particular the E. faecalis and E. faecium species which have been implicated in severe infections of the central nervous system and the urinary tract as well as intra-abdominal and pelvic infections, endocarditis, and bacteremia. Both species include strains that are widely used as probiotics. Enterococci do not possess the common virulence factors found in pathogenic bacteria, but they display other important biological traits, including the presence of drug-resistance genes and the production of cytolysin, adhesins, invasins, and gelatinase, which may represent a major threat to public health. Furthermore, many of these biological characteristics contributing to the virulence of enterococci are associated with pheromone-responsive conjugative plasmids. For the aforementioned reasons there is an urgent need for further research based on modern molecular techniques for a more accurate characterization and safety assessment of the enterococcal strains used in food and drug technology.

The aim of this special issue is to give an overview of the pros and cons of this controversial bacterial genus, as a full picture of the beneficial and virulent traits is needed to allow the identification of the truly harmless and beneficial enterococcal strains for the safe use as starter cultures in food systems or probiotics.

Potential topics include but are not limited to the following:

• Study of pathogenicity determinants and antibiotic resistance profiles of enterococci
• Factors contributing to enterococci antibiotic resistance and horizontal transmission of virulent traits
• Characterization of novel enterocins exhibiting activity against food borne pathogens
• Evaluation of functional, safety, and probiotic properties of enterococci
• Characterization of marine bacteriocinogenic enterococci endowed with inhibitory activity against fish-pathogenic bacteria
• Enterococcal bacteriocins and antimicrobial proteins that promote ecological niche control and the regulation of population dynamics in bacterial ecosystems