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Personne :
Ackermann, Hans-W.

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Ackermann

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Hans-W.

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Université Laval. Département de microbiologie-infectiologie et d'immunologie

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ncf10474077

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  • PublicationRestreint
    Characterization of a new virulent phage (MLC-A) of Lactobacillus paracasei
    (American Dairy Science Association, 2010-03-03) Capra, María Luján; Moineau, Sylvain; Luján Quiberoni, Andrea del; Ackermann, Hans-W.; Reinheimer, Jorge Alberto
    A new virulent bacteriophage (MLC-A) was recently isolated in Argentina from a probiotic dairy product containing a strain of Lactobacillus paracasei. Observation of the lysate with an electron microscope revealed bacteriophage particles with an icosahedral capsid of 57 ± 2 nm; with a collar and a noncontractile tail of 156 ± 3 nm terminating with a baseplate to which a tail fiber was attached. Therefore, phage MLC-A belongs to the Siphoviridae family. This phage was able to survive the pasteurization process and was resistant to alcohols and sodium hypochlorite (400 mg/kg). Only peracetic acid could inactivate high-titer suspensions of phages in a short time. The maximum rates of phage adsorption to its host cells were obtained at 30°C with a pH between 5 and 7, and in the presence of calcium or magnesium ions. The host range of phage MLC-A encompassed L. paracasei and Lactobacillus casei strains, but it was not able to infect Lactobacillus rhamnosus or Lactobacillus gasseri strains. One-step growth kinetics of its lytic development revealed latent and burst periods of 30 and 135 min, respectively, with a burst size of about 69 ± 4 plaque-forming units per infected cell. Phage MLC-A had a distinctive restriction profile when compared with the 2 well-studied Lactobacillus phages, PL-1 and J-1. The genome size of the MLC-A phage was estimated to be approximately 37 kb. This study presents the description of the first phage specific for L. paracasei isolated in Argentina. The isolation of phage MLC-A indicates that, beside lactic acid bacteria starters, probiotic cultures can also be sensitive to virulent phages in industrial processes.
  • PublicationRestreint
    Characterization of lactococcal bacteriophages from Quebec cheese plants
    (National Research Council, 1992-09-01) Moineau, Sylvain; Pandian, Sithian; Ackermann, Hans-W.; Fortier, Josée
    This is the first study on the characterization of lactococcal phages isolated in Canada. Thirty lactococcal phages were isolated from Quebec cheese plants reporting partial loss of starter activity. Phages were characterized by electron microscopy, DNA homology, protein profile, and host range. All phages belonged to the Siphoviridae family. Seventeen phages (57%) has prolate heads (60 × 40 nm) and 100 nm long, noncontractile tails (morphotype B2, species c2). They showed strong DNA homology with other prolate-headed phages isolated from other countries (Australia, United States). In addition to normal prolate phages, most lysates contained pairs of empty heads (no DNA) connected by a small bridge. Thirteen phages (43%) had small isometric heads (55 nm in diameter) and long, noncontractile tails (morphotype B1). Based on DNA homology, 11 of these phages were found related to phage species 936 despite differences in tail length (140 to 200 nm). The two other small isometric phages, UL36 and UL39, hybridized with phage P335 DNA, and therefore belong to this species. No DNA homology was observed between prolate and small isometric phages. Phages with prolate heads showed a broader host range than small isometric-headed phages. The DNA of phage UL36, which has a relatively narrow host range, has more restriction endonuclease sites than other lactococcal bacteriophages.
  • PublicationRestreint
    Diversity of streptococcus thermophilus phages in a large-production cheese factory in Argentina
    (Elsevier Inc., 2006-10-01) Luján Quiberoni, Andrea del; Tremblay, Denise; Moineau, Sylvain; Ackermann, Hans-W.; Reinheimer, Jorge Alberto
    Phage infections still represent a serious risk to the dairy industry, in which Streptococcus thermophilus is used in starter cultures for the manufacture of yogurt and cheese. The goal of the present study was to analyze the biodiversity of the virulent S. thermophilus phage population in one Argentinean cheese plant. Ten distinct S. thermophilus phages were isolated from cheese whey samples collected in a 2-mo survey. They were then characterized by their morphology, host range, and restriction patterns. These phages were also classified within the 2 main groups of S. thermophilus phages (cos- and pac-type) using a newly adapted multiplex PCR method. Six phages were classified as cos-type phages, whereas the 4 others belonged to the pac-type group. This study illustrates the phage diversity that can be found in one factory that rotates several cultures of S. thermophilus. Limiting the number of starter cultures is likely to reduce phage biodiversity within a fermentation facility.