Thermal and chemical inactivation of indigenous Streptococcus thermophilus bacteriophages isolated from Argentinian dairy plants.

BINETTI, A. G.; REINHEIMER, J. A.

JOURNAL OF FOOD PROTECTION

INT ASSOC FOOD PROTECTION

Año: 2000 vol. 63 p. 509 - 515

0362-028X

            Thermal and chemical resistance of five autochthonal bacteriophages of Streptococcus thermophilus, isolated from Cuartirolo cheese wheys and yogurth, was investigated. Times to obtain 99 % inactivation of phages (T99) at 63°C and 72°C in three suspension media (enriched tryptic soy broth, reconstituted commercial nonfat skim milk and tris magnesium gelatin buffer) were determined. The thermal resistance was dependent on the phages studied, but a complete inactivation of them was achieved by heating at 90°C during 5 min. The data obtained for the three assayed media did not permit verifying significant differences among them. Sodium hypochlorite (100 ppm) provided a fast inactivation of bacteriophage particles (<10 PFU/ml at 5 min). Ethanol, at concentrations of 75 % and 100 %, was also effective for phage destruction. The bacteriophage sensitivity to isopropanol was slightly less effective than ethanol at the same concentrations. Peracetic acid (0.15 %) was also a very effective agent for phage inactivation. The results showed that these authoctonal bacteriophages were not completely inactivated neither by normal pasteurisation treatments nor by some biocides commonly used in desinfection, except sodium hypochlorite and peracetic acid. The practical implications of these findings have pointed out the necessity of recognising the importance of establishing adequate conditions to assure effective thermal and chemical treatments in dairy plants and laboratory environments.