title: Population dynamics of two antilisterial cheese surface consortia revealed by temporal temperature gradient gel electrophoresis.
abstract: BACKGROUND
  Surface contamination of smear cheese by Listeria spp. is of major concern for the industry. Complex smear ecosystems have been shown to harbor antilisterial potential but the microorganisms and mechanisms involved in the inhibition mostly remain unclear, and are likely related to complex interactions than to production of single antimicrobial compounds. Bacterial biodiversity and population dynamics of complex smear ecosystems exhibiting antilisterial properties in situ were investigated by Temporal temperature gradient gel electrophoresis (TTGE), a culture independent technique, for two microbial consortia isolated from commercial Raclette type cheeses inoculated with defined commercial ripening cultures (F) or produced with an old-young smearing process (M).
  
  
  RESULTS
  TTGE revealed nine bacterial species common to both F and M consortia, but consortium F exhibited a higher diversity than consortium M, with thirteen and ten species, respectively. Population dynamics were studied after application of the consortia on fresh-produced Raclette cheeses. TTGE analyses revealed a similar sequential development of the nine species common to both consortia. Beside common cheese surface bacteria (Staphylococcus equorum, Corynebacterium spp., Brevibacterium linens, Microbacterium gubbeenense, Agrococcus casei), the two consortia contained marine lactic acid bacteria (Alkalibacterium kapii, Marinilactibacillus psychrotolerans) that developed early in ripening (day 14 to 20), shortly after the growth of staphylococci (day 7). A decrease of Listeria counts was observed on cheese surface inoculated at day 7 with 0.1-1 x 10(2) CFU cm(-2), when cheeses were smeared with consortium F or M. Listeria counts went below the detection limit of the method between day 14 and 28 and no subsequent regrowth was detected over 60 to 80 ripening days. In contrast, Listeria grew to high counts (10(5) CFU cm(-2) on cheeses smeared with a defined surface culture.
  
  
  CONCLUSIONS
  This work reports the first population dynamics study of complex smear ecosystems exhibiting in situ antilisterial activity. TTGE revealed the presence of marine lactic acid bacteria that are likely related to the strong Listeria inhibition, as their early development in the smear occurred simultaneously with a decrease in Listeria cell count.
authors.affiliation: Laboratory of Food Biotechnology, Institute of Food Science and Nutrition, ETH-Zurich, 8092 Zurich, Switzerland.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Roth
authors.forename: Susanne
authors.initials: S
authors.lastname: Miescher Schwenninger
authors.forename: Madlen
authors.initials: M
authors.lastname: Hasler
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Eugster-Meier
authors.forename: Christophe
authors.initials: C
authors.lastname: Lacroix
mesh_terms: D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification*; D002611:Cheese / Q000382:microbiology*; D015169:Colony Count, Microbial; D016172:DNA Fingerprinting; D016208:Databases, Factual; D004587:Electrophoresis, Agar Gel / Q000379:methods*; D005506:Food Contamination / Q000032:analysis; D005798:Genes, Bacterial / Q000235:genetics; D008087:Listeria / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification; D016133:Polymerase Chain Reaction; D011157:Population Dynamics; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D013696:Temperature
chemical_list: D012336:RNA, Ribosomal, 16S