Genomic typing of Streptococcus uberis isolates from cases of mastitis, inNew Zealand dairy cows, using pulsed-field gel electrophoresis

Three hundred and forty-two Streptococcus uberis isolates were cultured fro m milk samples from subclinical and clinical cases of dairy cattle mastitis . The samples were collected from 15 different New Zealand farming regions, including eight specific farms, during field research trials and veterinar y diagnostic investigations. Pulsed-field gel electrophoresis was used to d etermine and compare the degree of genetic dissimilarity between the restri ction endonuclease fragment pattern of the 342 New Zealand and a single Uni ted States S. uberis isolate. The 343 isolates exhibited 330 different rest riction endonuclease fragment patterns. The United States isolate had a pat tern unlike any of the New Zealand isolates. Most of the isolates were gene tically different strains (pattern deferred by at least 33%). but identical patterns were noted within the same or different quarters of an individual cow, different cows within the same farm, and from different cows from the same or different districts, fanning regions or islands. Seven of the eigh t selected farms had at most only one pair of isolates with banding pattern s, which differed by less than 33%. A high degree of dissimilarity was note d in individual herds in which all the samples were collected on the same d ay or over a 2-year period. The high degree of dissimilar isolates is an in dication that S. uberis infections in New Zealand dairy, cattle are largely due to the opportunistic nature of the organism in the cows' environment. Prevention and treatment of S. uberis mastitis will therefore need to be di rected at a multitude of different strains present throughout the country a s well as in individual herds. (C) 2000 Elsevier Science B.V. All rights re served.