Thermal and chemical inactivation of Lactobacillus virulent bacteriophage

Abstract

The effect of thermal treatments and several biocides on the viability of Lactobacillus virulent phage P1 was evaluated. Times to achieve 99% inactivation (T) of phage at different treatment conditions were calculated. The thermal treatments applied were 63, 72, and 90°C in 3 suspension media (de Man, Rogosa, Sharpe broth, reconstituted skim milk, and Tris magnesium gelatin buffer). Phage P1 was completely inactivated in 5 and 10 min at 90 and 72°C, respectively; however, reconstituted skim milk provided better thermal protection at 63°C. When phage P1 was treated with various biocides, 800 mg/L of sodium hypochlorite was required for total inactivation (∼7.3 log reduction) within 60 min, whereas treatment with 100% ethanol resulted in only a ∼4.7 log reduction, and 100% isopropanol resulted in a 5.2-log reduction. Peracetic acid (peroxyacetic acid) at the highest concentration used (0.45%) resulted in only a ∼4.-log reduction of phage within 60 min. The results of this study provide additional information on effective treatments for the eradication of potential phage infections in dairy plants.

Thermal-Stability and Reconstitution Ability of Listeria Phages P100 and A511

“…Linearity in P100 and A511 regression model affirmed rather homogenous population by virtue of thermal-stability in phage preparation. Unlike dairy phages which have been reported to be stable to 63°C ( Quiberoni et al, 2003 ; Ebrecht et al, 2010 ; Chen et al, 2017 ), P100 and A511 exhibited sensitivity to heat and instability at 65°C ( Table 1 ). Although both phages infect the same host species, they show significant differences in their thermal-stability.…”

“…Viral inactivation by thermal treatment has been previously studied ( Wilkowske et al, 1954 ; Caldentey et al, 1993 ; Moroni et al, 2002 ; Müller-Merbach et al, 2005 ; Buzrul et al, 2007 ; Atamer et al, 2013 ; Jurczak-Kurek et al, 2016 ; Chen et al, 2017 ), yet reconstitution during cooling phase after heating treatment has not been widely investigated. Zairi et al (2014) investigated the effects of heating and cooling cycle (60°C and cooled to 10°C) on gp12 capsid fiber of Bacillus phage SPP1 in a buffer solution [500 mm NaCl and 50 mm Na 2 HPO 4 (pH 8.0)] with a Fluorescence-based Thermal Shift Assay.…”

Inactivation of Dairy Bacteriophages by Thermal and Chemical Treatments

“…In recent studies, two phages (P1 and P2) isolated from an abnormal broth fermented with Lb. plantarum IMAU10120, showed a lower heat resistance since they were completely inactivated at 63 and 70 °C within 40–50 min and 10–20 min, respectively [37,39]. In both cases, a slightly higher resistance (protective effect) in media usually used in the dairy industry (milk skim and EM medium) was evidenced in comparison to the results obtained in laboratory media: the TMG buffer and MRS broth (Biokar, Beauvais, France) [34,37,39].…”

“…plantarum strains). For these phages, large phage particle numbers were found after 60 min, even at concentrations of 0.45% for this biocide [37,39]. On the contrary, alcohols in general showed low efficiency for phage inactivation.…”

“…In a similar way, phages P1 and P2 (isolated from a slow fermentation containing Lb. plantarum IMAU10120) were studied for their resistance to chemical products [37,39]. Here, phage P1 showed higher resistance to sodium hypochlorite, since 800 ppm were needed for its complete inactivation within 60 min [37].…”