TESTING OF THE VIRUCIDAL ACTIVITY OF DISINFECTANTS WITH BACTERIOPHAGES OF LACTIC-ACID BACTERIA

To test the virucidal activity of disinfectants used in the area of fo od processing, virulent bacteriophages of lactic acid bacteria were ch osen as model viruses for the preparation of a European CEN-standard, since these phages are wide-spread in dairies. For this quantitative s uspension test, the well-characterized Lactococcus lactis phages P001 (prolate-headed phage type) and P008 (isometric-headed phage type) wer e used, which have already been deposited in national and internationa l reference culture collections. The suitability of the method was als o demonstrated for a virulent (isometric-headed) phage of Streptococcu s thermophilus (phage P53), since phages of this bacterial species hav e recently also been reported to cause significant decreases of lactic acid production in the factories. High-titer stock lysates were obtai ned, when phage-derived plaques were harvested from agar plates reveal ing confluent lysis (titer ranging from 1 x 10(11) - 8 x 10(11) plaque forming units [PFU] per mi). The stock phage lysates were diluted to obtain virus working suspensions revealing a titer of 1 x 10(9) PFU/ml . To consider interfering proteinaceous substances, virucidal activity was tested in the presence of 1% (v/v) acidic whey or- optionally -1% (v/v) skim milk. After incubation at room temperature (20 degrees C), the test samples were diluted 50-fold in a validated neutralization so lution. The phages tested revealed different levels of resistance. The titers of the stock lysates remained stable for several months. The p hage lysates could be used for the test method during a storing period of several months at 4 degrees C without a significant effect on repr oducibility, indicating that sensitivity to disinfectants was not affe cted by the age of the lysates.