Thermal, Chemical, and Photocatalytic Inactivation of Lactobacillus plantarum Bacteriophages

Abstract

The effect of several biocides, thermal treatments, and photocatalysis on the viability of four Lactobacillus plantarum phages was investigated. Times to achieve 99% inactivation (T99) of phages at 63, 72, and 90 degrees C were evaluated in four suspension media: deMan Rogosa Sharpe broth, reconstituted skim milk, a commercial EM-glucose medium, and Tris magnesium gelatin buffer. The four phages studied were highly resistant to 63 degrees C (T99 > 45 min); however, counts < 10 PFU/ml were achieved by heating at 90 degrees C for 5 min. Higher thermal resistance at 72 degrees C was observed when reconstituted skim milk and EM-glucose medium were assayed. Peracetic acid (0.15%, vol/vol) was an effective biocide for the complete inactivation of all phages studied within 5 min of exposure. Sodium hypochlorite (800 ppm) inactivated the phages completely within 30 min. Ethanol (100%) did not destroy phage particles even after 45 min. Isopropanol did not have any effect on phage viability. Phage counts < 50 PFU/ml were obtained within 180 min of photocatalytic treatment. The results obtained in this work are important for establishing adequate methods for inactivating phages in industrial plants and laboratory environments.

Review: Efficiency of Physical and Chemical Treatments on the Inactivation of Dairy Bacteriophages

“…This fact remarks the importance of consider both parameters when defining the heat sensitivity of a given phage. Similarly to phage Ib 3 , destruction of total viral populations for the above mentioned heat-resistant phages was generally not achieved at this temperature, since detectable viable phage particles were found even after 45 min of treatment, which is a much longer period than that normally applied in the dairy industry for milk sanitization (Quiberoni et al, 1999, 2003; Binetti and Reinheimer, 2000; Suárez and Reinheimer, 2002; Briggiler Marcó et al, 2009). Dissimilar susceptibility to short-time pasteurization conditions (72°C for 30 s) was found for two Lactococcus phages; whereas one of them was complete and rapidly inactivated (loss of 7 log orders), the other one was highly heat-resistant (reduction of 2 log orders) and remained viable even after 60 min of treatment (Müller-Merbach et al, 2005).…”

“…Among the latter, it is worth noticing phages hv ( Lactobacillus helveticus ), Cb1/204 ( Lactobacillus delbrueckii ), PL-1 and J-1 ( Lactobacillus casei and Lactobacillus paracasei ), which showed very low T 99 values (from 2.1 to 3.1 min) in all suspension media tested (Quiberoni et al, 1999; Capra et al, 2004; Ebrecht et al, 2010). In spite of the high heat sensitivity to 63°C shown by some Lactobacillus phages, there were others capable to easily resist this treatment, as demonstrated by Lactobacillus plantarum phages investigated by Briggiler Marcó et al (2009) ( T 99 values > 45 min).…”

“…thermophilus), at 72°C using reconstituted skim milk as suspension media . Data adapted from Binetti and Reinheimer (2000), Quiberoni et al (2003), and Briggiler Marcó et al (2009). …”

“…On the contrary, 40% of L. lactis phages tested were able to resist 80°C for 5 min (Atamer et al, 2009), whereas 70% of Leuconostoc phages particles were still detectable after 1 min at this temperature (Atamer et al, 2011). Until recently, heat treatment at 90°C for 5 min was sufficient for inactivation of phage particles (Binetti and Reinheimer, 2000; Suárez and Reinheimer, 2002; Capra et al, 2004; Briggiler Marcó et al, 2009). Despite this, in the last years some extraordinarily heat-resistant phages are being found in many research laboratories, such as phage Ib 3 ( Lb .…”

Exposing the Secrets of Two Well-Known Lactobacillus casei Phages, J-1 and PL-1, by Genomic and Structural Analysis

“…Strategies to control this contamination include milk pasteurization and sanitation of equipment (6)(7)(8)(9), but phages are rarely completely eliminated. Cultures of starter strains themselves can be phage contaminated, likely due to induction of resident prophages and concomitant cell lysis (10)(11)(12)(13).…”