Widely distributed lysogeny in probiotic lactobacilli represents a potentially high risk for the fermentative dairy industry

• Published in: International journal of food microbiology 2011-01, Vol.144 (3), p.503-510
• Main Authors: Mercanti, Diego J., Carminati, Domenico, Reinheimer, Jorge A., Quiberoni, Andrea
• Format: Article
• Language: English
• Subjects: Bacteriophages - drug effects; Bacteriophages - genetics; Bacteriophages - pathogenicity; Bacteriophages - physiology; Biological and medical sciences; Cultured Milk Products - microbiology; Cultured Milk Products - virology; dairy industry; dairy products; Dairying; DNA, Bacterial - genetics; fermented foods; food analysis; food composition; Food industries; Food microbiology; Fundamental and applied biological sciences. Psychology; genome; Lactobacillus; Lactobacillus - classification; Lactobacillus - drug effects; Lactobacillus - genetics; Lactobacillus - virology; Lactobacillus casei; Lactobacillus casei - classification; Lactobacillus casei - genetics; Lactobacillus casei - virology; Lactobacillus paracasei; Lactobacillus rhamnosus; Lactobacillus rhamnosus - classification; Lactobacillus rhamnosus - genetics; Lactobacillus rhamnosus - virology; Lysogeny; microbiological risk assessment; Milk and cheese industries. Ice creams; Mitomycin - pharmacology; model food systems; Nucleic Acid Synthesis Inhibitors - pharmacology; Phylogeny; Probiotic bacteria; Probiotics; prophages
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2010.11.009

Prophages account for most of the genetic diversity among strains of a given bacterial species, and represent a latent source for the generation of virulent phages. In this work, a set of 30 commercial, collection and dairy-isolated Lactobacillus casei group strains were used. A species-specific PCR assay allowed a reclassification, mainly of strains previously considered Lactobacillus casei, into either Lactobacillus paracasei or Lactobacillus rhamnosus. All the strains were induced with mitomycin C, allowing direct recovering of phage DNA in 25 cases, which corroborates the widely occurrence of lysogeny on Lactobacillus genomes, including probiotic strains of Lactobacillus casei group. Ten out of 11 commercial strains studied contained prophages, evidencing the potential risks of their use at industrial scale. Strains were also induced by treatment with different concentrations of hydrogen peroxide but, however, this agent was not able to evidence a prophage release for any of the strains tested. According to a RAPD-PCR fingerprinting with M13, 1254 and G1 primers, most of the commercial strains presented a high degree of homology and, regarding BglII- and BamHI-restriction profiles of phage DNA, six of them harboured the same prophage. Surprisingly, both Lactobacillus paracasei ATCC 27092 and Lactobacillus paracasei ATCC 27139 shared a second prophage with both an INLAIN collection and a commercial Lactobacillus paracasei strains, whereas two collection strains shared a third one. On the other hand, mitomycin C-inducible prophages were detected only on about a half of the strains isolated from dairy products, which had (with only one exception) from moderate to high correlation coefficients according to RAPD-PCR fingerprinting. After induction, supernatants were filtered and tested against nine Lactobacillus strains of the set sensitive to previously assayed virulent phages, allowing isolation of two new virulent phages: ф iLp1308 and ф iLp84. Both phages were able to lyse all but one strains sensitive to previously assayed phage MLC-A. ►25 out of 30 strains of Lactobacillus of the casei group tested harboured prophages. ►Commercial probiotic lactobacilli usually comprise highly related lysogeny strains. ►The same or different prophages can be present in highly related probiotic strains. ►Mitomycin C lead to the release of 2 new virulent phages in probiotic lactobacilli.