Phenotypic and Genotypic Characterization of Pseudomonas fluorescens Isolated from Bulk Tank Milk

摘要

Pseudomonas fiuorescens isolates (n = 55) isolated from farm bulk tank milk (n = 55) from dairy herds in eastern South Dakota and western Minnesota were examined for phenotypic (biotroe, proteolytic, and lipo- lytic profiles) and genotypic (plasmid profiles and 16S- 23S PCR ribotypes) characteristics. The observed phe- notypic and genotypic characteristics were used to con- duct phylogenetic analysis. Pseudomonas fluorescens belonged to 28 API 20 NE biotypes and 14 proteolytic and lipolytic profiles. It was observed that 80, 91, and 58/100 of the isolates were proteolytic at 7, 22, and 32 deg. C, respectively. Only 7, 44, and 7/100 of the isolates were lipolytic at the same three temperatures. Pseudomonas fiuorescens was more likely to produce proteinases at 7 and 22 deg. C and lipases at 22 deg. C. Only 9 of 55 isolates of P. fluorescens harbored plasmids. This small percent- age of plasmid-bearing isolates provided insufficient data for inferences related to the distribution of plas- mid-bearing clonal types. Based on 16S-23S PCR ribo- tyPing, P. fluorescens belonged to 14 subtypes. The 16S- 23S PCR ribotyping technique allowed differentiation between strains; however, it did not concur with the biotypes and proteolytic and lipolytic profiles. Use of biotypes in conjunction with proteolytic and lipolytic profiles might have practical value for conducting trace- back studies related to P. fluorescens. Based on phyloge- netic analysis, it was inferred that for the given geo- graphical area and time period, P. fluorescens isolated from farm bulk tank milk consists of a large heteroge- neous group of organisms.