CONICET | Buscador de Institutos y Recursos Humanos

The implementation of effective treatments to minimize phage attacks on lactic bacteria in dairy industry is mandatory. No reports are available regarding biocides applied in cheese and yogurt factories. In this work, the effect of biocide treatments on the inactivation of two temperate phages (Cb1/342 and Cb1/204) and three virulent phages (BYM, YAB and Ib3) of L. delbrueckii was investigated. Five commercial biocides (A, B, C, D and E) were assayed. All biocides were used under the conditions recommended by the suppliers. Results were expressed as concentration (PFU/ml) of survival viral particles and plotted against time. The time (min) required to achieve 99% of inactivation (T99) was calculated from survival kinetics. In order to test the influence on phage viability, adequate pH controls were included. Biocides A, B and C produced a fast and complete inactivation of phage particles, since no detectable counts were obtained after 2 min of treatment. Biocide D (0.13%, v/v) inactivated temperate and virulent phages (phages BYM and YAB) after 2 min, whereas for phage Ib3 the T99 value was of 8 min. Concentrations of 0.26% (v/v) achieved the total inactivation of phage Ib3 after 10 min. Biocide E was less effective, since more than 99% of particles remained viable after 45 min for virulent phages and for Cb1/342; whereas Cb1/204 showed a T99 value of 17.3 min. Extreme pH values of biocides B and C (12.4 and 2.0, respectively) showed influence in the inactivation of phages. This behavior was not observed for the others.This study allowed us having a better knowledge concerning L. delbrueckii phages resistance against chemical agents used in disinfection of industrial dairy plants.