CONFERENCIA: Bacteriofagos y la industria fermentativa de alimentos. ¿Cómplices o enemigos?

QUIBERONI, A.

Buenos Aires

Congreso; XII Congreso Argentino de Microbiología, VI Congreso de Sociedad Argentina de Bacteriología, Micología y Parasitología Clínica y I Congreso de Microbiología Agrícola y Ambiental; 2010

Asociación Argentina de Microbiología

Lactic acid bacteria in active development are at risk of suffering phage attacks, an always-present threat in all dairy plants. Bacteriophage infections on probiotic bacteria are difficult to overcome because of the singularities of these valuable strains, which make them ‘unique’. Due to phage ubiquity in dairy environments, researches are directed to its control, instead of its removal, by implementing diverse practical measures. Nevertheless, severe limitations are found when fighting against probiotic bacteria phages.Harbored prophages in lysogenic strains are one of the main sources of phages in the dairy industry, thus the strain selection programs should include a screening to detect and remove them from the list of alternatives. However, it seems that lysogeny is a distinctive feature of several strains of Lactobacillus casei / paracasei used in the manufacture of fermented milks, and it is also common in Lactobacillus gasseri, Lactobacillus johnsonii, Lactobacillus plantarum and Lactobacillus rhamnosus.Implications of lysogeny in probiotic lactic acid bacteria are very complex and still scarcely known, affecting not only the food processing technology but their functional attributes. Specifically, prophages are known to contribute significantly to the diversification and instability of bacterial genomes, providing in some cases competitive advantages to lysogenic strains. There is also evidence of bacterial virulence in pathogens associated with the presence of prophages, as the expression of toxins, enzymes or virulence factors in Staphylococcus aureus and Streptococcus pneumoniae. Similarly, prophages in the chromosome of probiotic bacteria could be related to the expression level of a particular probiotic attribute, so the relationship between lysogeny, bacterial functionality, and genetic stability over time should be explored thoroughly. Prophages of probiotic lactic acid bacteria are no longer considered as inert entities in the cellular genome.Unfortunately, there are still a few complete nucleotide sequences reported for prophages of probiotic lactic acid bacteria. However, phylogenetic analyses of these sequences have confirmed that phages A2, ФAT3, Lca1 and Lc-Nu share a common ancestor. Astonishingly, the first three are prophages of L. casei, whereas Lc-Nu is a virulent phage of L. rhamnosus. These facts confirm the hypothesis of a temperate origin, postulated previously for several virulent Lactobacillus phages. Undoubtedly, detailed knowledge of more of these prophage genomes will enhance the understanding of their role in relation to their lysogenic hosts and the evolution of virulent phages in industrial environments.