Aplicación de fagos de Enterococcus faecalis para evitar la acumulación de aminas biógenas en queso

Abstract

Biogenic amines (BA) are low molecular weight nitrogenous bases that are synthesized by decarboxylation of certain amino acids and play essential roles in all living organisms. However, their accumulation in elevated concentrations in foods ¿mainly due to the metabolic activity of certain bacteria- constitutes a toxicological hazard to consumer health (Ladero et al., 2010; EFSA, 2011). Foods likely to contain high levels of BA include fish, fish products and fermented foods (meat, dairy products or vegetables) and beverages (wine, cider and beer) (Spano et al., 2010). The bacteria responsible for BA accumulation in fish are gram negative bacteria that contaminate the food due to bad hygienic practices. However, the BA producers in fermented foods belong generally to the lactic acid bacteria group (LAB) and the measures to reduce their population also affect other LAB that play an essential role in the fermentation an the organoleptic characteristics of these foods. Cheeses is one of the foods that can accumulate very high concentrations of BA , since they constitute an ideal environment for BA accumulation: the raw material -the milk- is not sterile, BA-producing bacteria belong to its normal microbiota, the proteolysis of casein provides high concentrations of amino acids substrate, and physico-chemical conditions for optimal elaboration (pH, temperature, etc) favors their biosynthesis (Linares et al., 2012). Most of the proposed methods towards the reduction of BA in cheeses -such as pasteurization- are not completely effective and affect LAB that actively participates in the development of the organoleptic characteristics of cheeses. Thus novel technologies specifically targeted against BA producers are needed to reduce the content of BA in cheeses. Bacteriophages present several advantages for their use as biocontrol agents in food products. They are considered as safe, kill their host bacteria at low doses -they are self-replicating- and very specifically. Bacteriophages have been tested to control the presence of foodborne pathogens (Mahony et al., 2011), but not as agents to reduce the population of spoilage bacteria. In the present work, we have isolated from cheese, and characterized the bacteriophage Q69, which infects Enterococcus faecalis, the species mainly responsible for the accumulation of tyramine in cheese . Subsequently, we found that the phage Q69 was able to reduce the accumulation of tyramine -the most toxic and frequently found biogenic amine in cheese- in different laboratory conditions. We present these data as a proof-of-concept for the application of phages to reduce the accumulation of BA in fermented foods and consequently reduce the health risks associated to their consumption.