Raw cow milk bacterial population shifts attributable to refrigeration.
We monitored the dynamic changes in the bacterial population in milk associated with refrigeration. Direct analyses of DNA by using temporal temperature gel electrophoresis (TTGE) and denaturing gradient gel electrophoresis (DGGE) allowed us to make accurate species assignments for bacteria with low-GC-content (low-GC%) (<55%) and medium- or high-GC% (>55%) genomes, respectively. We examined raw milk samples before and after 24-h conservation at 4 degrees C. Bacterial identification was facilitated by comparison with an extensive bacterial reference database ( approximately 150 species) that we established with DNA fragments of pure bacterial strains. Cloning and sequencing of fragments missing from the database were used to achieve complete species identification. Considerable evolution of bacterial populations occurred during conservation at 4 degrees C. TTGE and DGGE are shown to be a powerful tool for identifying the main bacterial species of the raw milk samples and for monitoring changes in bacterial populations during conservation at 4 degrees C. The emergence of psychrotrophic bacteria such as Listeria spp. or Aeromonas hydrophila is demonstrated.
Lafarge
Véronique
V
Unité Composition et Hygiène des Produits Laitiers, Agence Française de Sécurité Sanitaire des Aliments, 39-41 rue du 11 novembre 1918, 94700 Maisons Alfort, France. v.lafarge@afssa.fr
Ogier
Jean-Claude
JC
Girard
Victoria
V
Maladen
Véronique
V
Leveau
Jean-Yves
JY
Gruss
Alexandra
A
Delacroix-Buchet
Agnès
A
D000818:Animals; D001419:Bacteria / Q000235:genetics / Q000302:isolation & purification*; D001483:Base Sequence; D002417:Cattle; D017931:DNA Primers; D004586:Electrophoresis / Q000379:methods; D005511:Food Handling; D008892:Milk / Q000382:microbiology*; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction / Q000379:methods; D012329:RNA, Bacterial / Q000235:genetics / Q000302:isolation & purification; D012336:RNA, Ribosomal, 16S / Q000235:genetics / Q000302:isolation & purification; D012034:Refrigeration / Q000379:methods*
D017931:DNA Primers; D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S