Isolation and Characterization of a Novel Virulent Phage of Lactobacillus casei ATCC 393

Abstract

A new virulent phage (Lcb) of Lactobacillus casei ATCC 393 was isolated from Chinese sauerkraut. It was specific to L. casei ATCC 393. Electron micrograph revealed that it had an icosahedral head (60.2 ± 0.8 nm in diameter) and a long tail (251 ± 2.6 nm). It belonged to the Siphoviridae family. The genome of phage Lcb was estimated to be approximately 40 kb and did not contain cohesive ends. One-step growth kinetics of its lytic development revealed latent and burst periods of 75 and 45 min, respectively, with a burst size of 16 PFU per infected cell. The phage was able to survive in a pH range between 4 and 11. However, a treatment of 70 °C for 30 min and 75% ethanol or isopropanol for 20 min was observed to inactivate phage Lcb thoroughly. The presence of both Ca(2+) and Mg(2+) showed a little influence on phage adsorption, but they were indispensable to gain complete lysis and improve plaque formation. The adsorption kinetics were similar on viable or nonviable cells, and high adsorption rates maintained between 10 and 37 °C. The highest adsorption rate was at 30 °C. This study increased the knowledge on phages of L. casei. The characterization of phage Lcb is helpful to establish a basis for adopting effective strategies to control phage attack in industry.

Construction of Lactobacillus casei ghosts by Holin-mediated inactivation and the potential as a safe and effective vehicle for the delivery of DNA vaccines

“…In our previous work, a virulent phage against L. casei ATCC 393 was isolated from fermented vegetables and designated as Lcb [ 40 ]. The phage Lcb was purified and stored in our laboratory.…”

“…The deposit was then resuspended in SM (sodium-magnesium-buffered saline) buffer. Phage DNA was extracted by phenol–chloroform–isoamyl alcohol and then precipitated by isopropanol [ 40 ].…”

Inactivation of Dairy Bacteriophages by Thermal and Chemical Treatments

“…These studies demonstrated, as discussed for phages infective to other LAB genera, traditional pasteurization treatments (LTLT, 63 °C for 30 min and HTST, 72 °C for 15 s) would be not enough to reach complete inactivation of dairy phages, since most of them survive (in diverse levels) at these conditions. However, no phage particles were detected at 90 °C for 5 min, except for some phages infective to Lactobacillus delbrueckii [32,38] and Lactobacillus casei / paracasei [58,59], which keep their infectivity until 30 min at this temperature (depending on the phage). On the other hand, phages infecting lactobacilli showed diverse responses (phage-dependent behavior) when they were subjected to treatments at 63 and 72 °C for 45–60 min.…”

“…On the other hand, a lower thermal resistance was observed for a non-dairy phage (Lcb), isolated from Chinese sauerkraut when its thermal resistance was studied in MRS broth (Biokar, Beauvais, France). In this way, treatments at 70 °C for 30 min or at 80 °C for 10 min were enough to inactivate the entire phage particle population [38] (Table 4). As mentioned for St. thermophilus phages, those infective of Lb.…”

Bacteriophages and their applications

“…Most bacteriophages act optimally at temperatures between 30 -50˚C (Bao et al, 2015;Ji et al, 2015;Zhang et al, 2015). Bacteriophages were also found to be active over the temperature range of 4-50˚C (Jun et al, 2013) and 4-60˚C (Easwaran et al, 2015) for Shigella flexneri phage pSf-1 and Escherichia coli phage Sw1, respectively.…”