phenotypic characterizationand pcr-ribotyping of pseudomonas fluorescensisolates, in tracking contamination routes in the production line of pasteurized milk

contamination sites of pseudomonas fluorescenswere traced in the production line for milk pasteurization in a large dairy plant in shiraz, iran. samples of raw and pasteurized milk were collected at six sites along the line. all milk samples were incubated at 7°c until the aerobic plate count had reached 10 6 -10 7 cfu ml-1. colonies were picked randomly and identified. no growth of gram negative psychrotrophic bacteria (gnp) was detected in the immediately pasteurized milk samples (just after the pasteurization), during long incubation at 7°c.recontamination most often occurred in the filling step. in this study 34.1 and 4.9% of the milk packages showed contamination with gnp and p. fluorescens, respectively. twenty threep. fluorescensisolates were examined for phenotypic characteristics and 16s-23s pcr ribotyping. phylogenetic analysis was conducted on the phenotypic and genotypic characteristics. thep. fluorescensisolates were shown to belong to 6 biotypes (b1-b6). the predominance of a particular ribotype was often observed for a given biotype,although there were two ribotypes in eachof the b2 and b6 biotypes. the 16s-23s pcr-ribotyping technique allowed differentiation between the isolates. based on this method, the isolates belonged to 5 subtypes. phylogenetic analysis based on 16s-23s pcr-ribotyping and phenotypic characterization could be helpful in tracking contamination routes in the production line for milk pasteurization.