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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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Voici les éléments 1 - 3 sur 3
  • 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
    Streptococcus thermophilus bacteriophages
    (Elsevier Applied Science, 2010-04-14) Luján Quiberoni, Andrea del; Moineau, Sylvain; Rousseau, Geneviève M.; Ackermann, Hans-W.; Reinheimer, Jorge Alberto
    At least 345 bacteriophages infecting Streptococcus thermophilus starter cultures have been isolated; general characteristics include high thermal resistance, short latent periods and large burst size. Phages with such characteristics are primed to thrive in the cheese making environment, lysing bacterial cultures and generating low-quality fermented products. All S. thermophilus phages isolated to date are members of the Siphoviridae family and the Caudovirales order and appear to constitute a polythetic phage species comprising two large groups, cos- and pac-types, based on the mode of DNA packaging. Comparative analyses have shown that S. thermophilus phage genomes are similarly organized into distinct modular regions and allow the detection of a core genome region. Several PCR-based techniques have been designed to detect them in cheese whey and milk samples. Similar S. thermophilus phages are globally distributed and endemic in specific dairy environments. The biogeography of S. thermophilus phages reinforces their current classification.
  • 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.