An investigation of Pseudomonas fluorescens in the milk environment
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
The main aim of this study was to determine the percentage of Pseudomonas fluorescens amongst fluorescent pseudomonads in the milk environment, and to distinguish these isolates from each other. A secondary aim was to investigate whether these isolates were clonal or non-clonal in origin, and to study whether end product contamination had an endemic factory source. In this study 230 fluorescent bacteria were isolated from a South Island dairy company over a six month period. These bacteria were isolated from raw milk and associated environments, separated milk and associated environments, pasteurised milk environments and from final product sampling. These isolates were biotyped using the API-20NE biochemical test system. Approximately 70% of these isolates were identified as Ps. fluorescens, and the majority of these grouped into the biotypes 0157555 and 0357555. Strains of Ps. fluorescens grouped into these biotypes were the only proteolytic enzyme producers isolated from final product isolates. To investigate whether end product contamination had an endemic factory source, 97 strains of the biotypes 0157555 and 0357555 were characterised using the technique of multilocus enzyme electrophoresis. These strains clustered into 26 distinct electromorphs, with the majority of isolates falling into one cluster. Isolates in this cluster originated from raw milk and associated environments, separated milk and associated environments, the pasteurised milk environment and the final product. With the exception of month four there is a constant presence of the major cluster strains in the milk environment. This cluster can be divided further as both of the biotypes studied (0157555 and 0357555) were present in this group. Isolates in this major cluster could be clonal in origin and represent a serious contaminating organism able to occupy many niches in the milk processing environment over a considerable time period.