Phages of Lactobacillus casei/paracasei:: response to environmental factors and interaction with collection and commercial strains

Aim: To investigate the influence of several environmental factors on the viability and cell-adsorption for two Lactobacillus casei/paracasei bacteriophages (PL-1 and J-1). Methods and Results: Both phages showed a remarkably high specificity of species, sharing similar host spectra. Two phages and four sensitive strains were used to conform five phage/strain systems. Each showed a particular behaviour (burst size: ranging from 32 to 160 PFU/infective centre; burst time: 120-240 min and latent time: 5-90 min). For both phages, the viability was not significantly affected from pH 4 to 11 (room temperature) and from pH 5 to 10 (37 degrees C). Adsorption rates were not influenced by calcium ions, but decreased after the thermal inactivation of cells. Adsorption rates were high between 0 and 50 degrees C with maximum values at 30 degrees C and pH 6. System PL-1/Lact. paracasei A showed noticeable differences in comparison with the others, being times required to reach 90% of adsorption of 4 h and lower than 45 min, respectively. Conclusions: The data obtained in this work demonstrated that environmental parameters can influence the viability and cell adsorption rates of Lact. casei/paracasei phages. The extent of this influence was phage dependent. Significance and Impact of the Study: This work contributes to the enlargement of the currently scarce knowledge of phages of probiotic bacteria.