Phenotypic and genotypic characterization of Pseudomonas aeruginosa strains isolated from mastitis outbreaks in dairy herds

During 1998-2002 outbreaks of Pseudomonas sp. mastitis among more than 15 Israeli sheep and goat dairy herds were observed. The animals presented a wide spectrum of clinical signs ranging from subclinical to gangrenous udder. Ninety-five isolates of Pseudomonas sp. were isolated from clinical and subclinical mastitis of 47 sheep, 17 goats and 31 cows from 34 different farms. Biochemical and genetic analyses revealed that the all-causative organism was Ps. aeruginosa. Selections of isolates were further analysed on the bases of colony morphology, biochemical traits and capacity to form biofilm. All the strains displayed a wide heterogeneity in all the tested traits. No association between bacterial isolates, farm of origin and type of animal was found. Pulsed-field gel electrophoresis and cluster analysis showed no clonality among the tested strains. The present study revealed that a large variety of Ps. aeruginosa strains may cause mastitis outbreaks in sheep, goat and cattle in Israel.