In the present study, we investigated the variability of bovine clinical mastitis isolates of Streptococcus
uberis in Japan by multilocus sequence typing. We also investigated the variations in the primary
structure of the vru gene upstream region of the isolates to elucidate the association of this region with
the occurrence of clinical mastitis. Eighty-two isolates were recovered from 62 dairy farms in Japan;
these isolates were associated with 57 sequence types (STs), including 54 novel STs to which 78 isolates
belonged. Thirty isolates with ST1003 (one of the novel STs) and related STs at the triple-locus variant
level accounted for 37% of the isolates examined. A total 16 (20%) isolates were assigned to clonal
complexes (CC143 and CC86) that are major in New Zealand and Australia. Seventy-one of the 82 isolates
had 1, 3, 4 or 5 bp deletions in the vru gene upstream region in comparison with the corresponding
region in the S. uberis virulent strain 0140J and the remaining 11 isolates had no deletions. These
results suggest that S. uberis is a diverse mastitis-causing pathogen, and the integrity of the vru gene
upstream region is not necessarily conclusive for the occurrence of bovine clinical mastitis.
