Molecular analysis of Pseudomonas aeruginosa: Epidemiological investigation of mastitis outbreaks in Irish dairy herds

Pseudomonas aeruginosa is a pathogen in both humans and animals. This bacte rium, most often associated with respiratory infections in cystic fibrosis patients, was found to be the causative agent in bovine mastitis outbreaks among 11 Irish dairy herds. Epidemiological findings suggested that the inf ection was spread to all herds by teat wipes that had been contaminated wit h this organism. Two molecular-typing strategies were used in an attempt to determine the genomic relationship(s), if any, of the P. aeruginosa strain s isolated from the various herds and to verify whether the same strain was responsible for each outbreak Thirty-six isolates from the mastitis outbre aks were tested and compared to fourteen clinical isolates from Cork Univer sity Hospital. With one exception, all outbreak-linked strains produced ide ntical patterns when ribotyped with ClaI and PvuII enzymes. Eight of the cl inical isolates gave the same ClaI ribotype pattern as the mastitis-causing strains. However, PvuII proved more discriminatory, with only the outbreak isolates producing identical patterns. Similar results were obtained with RW3A-primed DNA amplification fingerprinting, with all outbreak isolates ex cept one displaying the same fingerprint array. The clinical strains produc ed several fingerprint patterns, all of which were different from those of the mastitis-causing isolates. Fine-resolution DNA fingerprinting with a fl uorescence-labelled RW3A primer also identified a number of low-molecular-w eight polymorphisms that would have remained undetected by conventional met hods. These data support the view that the same P. aeruginosa strain was re sponsible for the mastitis outbreaks in all 11 herds.