Bacteriophages of dairy propionibacteria

Two types of bacteriophage (phage) infecting dairy propionibacteria (PAB) w ere isolated from Swiss-type cheeses. One belongs to Bradley's classificati on group B1 and the other is, to our knowledge, the first infective filamen tous virus described in Gram positive bacteria. Both types of phages were p resent in several different Swiss-type cheeses. A possible source has been shown to be raw milk where they are found in small quantities. The B1 type phage can be harboured by PAB in the prophage state. DNA hybridization expe riments showed that all PAB B1 phages are closely related, although they we re isolated from different cheeses and probably have a common origin. As se nsitive strains can constitute the predominant PAB flora at the end of chee se ripening, it seems obvious that phage did not disturb the development of this flora and consequently did not have an unfavourable effect on the org anoleptic properties of Swiss-type cheeses. This information concerning pha ges allowed us to develop an efficient cloning system for Propionibacterium freudenreichii. (C) Inra/Elsevier, Paris.