ABSTRACT
Contamination sites of Pseudomonas fluorescens were 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[degree sign] 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 [degree sign] 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 three P. fluorescens isolates were examined for phenotypic characteristics and 16S-23S PCR ribotyping. Phylogenetic analysis was conducted on the phenotypic and genotypic characteristics. The P. fluorescens isolates 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 each of 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 form milk pasteurization