Short communication: Molecular typing of Prototheca zopfii from bovine mastitis in Japan

Prototheca zopfii causes bovine mastitis, resulting in reduced milk production and the secretion of thin watery milk with white flakes. Prototheca zopfii has been biochemically and serologically divided into at least 2 genotypes, P. zopfii genotype 1 and P. zopfii genotype 2. The latter is known to be the main causative agent of bovine protothecal mastitis. Prototheca zopfii was later reclassified into 5 varieties: var. zopfii (genotypes 1 and 2), var. 1 (formerly Prototheca blaschkeae), var. 3 (formerly P. moriformis), and var. portoricensis. In this study, the 18S ribosomal DNA sequences of diverse clinical specimens from different areas in Japan were studied to clarify the pathogenicity of P. zopfii var. zopfii. The phylogenetic tree revealed that all genotype 2 isolates were grouped in a cluster of P. zopfii var. zopfii SAG 2021T (type strain genotype 2), and were independent from the cluster of the genotype 1 isolates. Thus, all isolates from bovine mastitis in Japan were identified as P. zopfii genotype 2. Therefore, P. zopfii var. zopfii genotype 2 is associated with bovine mastitis.