Propionibacteria flora in Swiss raw milk from lowlands and Alps

The propionic acid bacterial flora in Swiss raw milk was investigated. Four hundred and fifty-three strains from lowland milk and 21 strains from Alpi ne raw milk were classified to the species level by protein profile analysi s and restriction analysis of the 23S ribosomal ribonucleic acid (rRNA). Pl asmid profiles and random amplified polymorphic deoxyribonucleic acid (RAPD ) was used to differentiate the strains. The flora was found to be extremel y diverse. All four dairy Propionibacterium species were found in lowland r aw milk: 71 % were P. freudenreichii, 19 % P. jensenii, 8 % P. acidipropion ici and 2 % P. thoenii. P. acidipropionici was not found in alpine milk but P. P. freudenreichii made up 55 %, P. jensenii 15 % and P. thoenii 30 % of the total. Among 278 P. freudenreichii strains, 219 (79 %) different strai ns were identified by RAPD to the strain level. For the other species strai n diversity was even greater. Only 30 % of the strains analyzed carried pla smids. The Swiss cheese industry has a large reservoir of Propionibacterium strains in raw milk for future applications and developments. (C) Inra/Els evier, Paris.