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Influence of Physical-Chemical Factors of Phages Isolated in Dairy Processing Plants of Ukraine

When establishing a bacteriophage control system, it is important to introduce new modern approaches to dairy production, including the use of effective, cost-profitable washing and disinfection programs that can provide not only microbiological but also virological safety for production and target products. At the same time, information on reliable anti-phage treatment in dairy processing plants is extremely limited. Aim. Investigation of the virucidal activity of some disinfectants, depending on the composition, treatment conditions and titer of phage contamination. Methods. The objects of the study were virulent phages F 11; F/2 of Lactococcus lactis ssp., isolated in dairy processing plants from the collection of the Institute of Food Resources of the NAAS of Ukraine; disinfectants approved for use in the dairy industry (LLC “Lizoform”, Kyiv). The virucidal activity of the disinfectants was evaluated by the difference between the phage titer values in sterile distilled water without and with the addition of the disinfectant after a certain treatment time. The sensitivity of phages to the effect of the disinfectant was characterized by a constant of inactivation (Cin). The presence of active phages was determined by the “double agar” method with the addition of 10 mmol·l-1 CaCl2, 100 mmol·l-1 glycine. Results. Screening of physical and chemical factors that inhibit the development of virulent phages F 11 and F/2 of Lactococcus lactis ssp. isolated in dairy processing plants of Ukraine was performed. It was found that the most detrimental effect on these phages had disinfectants with such active substances as peracetic acid (PA), quaternary ammonium compounds (QAC), and active chlorine (Cl2). It was determined that the minimum inhibitory concentrations of active chemical substance during “cold disinfection” at a temperature 20–22ºС were sufficiently high: for PA – 500–2000 mg·l-1 (p≤0.05); QAC – 900–1000 mg·l-1; Cl2 – 800–1000 mg·l-1, p≤0.01. Comparison of the phage inactivation rate with respect to the initial contamination level showed that phages in high titer 108 PFU·ml-1 (the most dangerous, critical level of contamination) were more resistant to treatment than phages in medium titer 106 PFU·ml-1. It was shown that the investigated phage F11 of Lactococcus lactis (936 species) were characterized by greater resistance to disinfectants compared to the phage F/2 of Lactococcus lactis (с2 species). Conclusions. The conditions of anti-phage treatment are experimentally substantiated. It is established that the effectiveness of disinfection depends on the type and concentration of the active chemical substance, as well as on the content and properties of phages that circulate in dairy processing plants of Ukraine.