Characterization of Prototheca zopfii Genotypes Isolated from Cases of Bovine Mastitis and Cow Barns in China.

Protothecal mastitis, caused mostly by Prototheca zopfii (P. zopfii), is increasing in dairy herds and is being reported globally. The present study was aimed at studying the epidemiology of mastitis and at molecular characterization of P. zopfii isolates from dairy herds and their surroundings in three provinces of China using microbiological, biochemical and molecular methods, and antibiotic susceptibility tests. Samples from milk (n = 620) of mastitic cows and their barns sources (n = 410) including feces, feed, bedding materials and drinking water were analyzed. Among other pathogens recovered from mastitic milk, 84 (13.5%) of the isolates were identified as P. zopfii. All of the P. zopfii isolates recovered from milk were recognized as genotype 2, whereas 58 (73.4%) and 21 (26.6%) isolates from environmental sources were found to be P. zopfii genotypes 1 and 2, respectively. The isolates were susceptible to some antibiotics and antifungal agents, including amikacin (78.1%), streptomycin (58.5%), gentamicin (17.8%), amphotericin B (68.6%) and nystatin (64.4%). Additionally, the two genotypes displayed versatile patterns of susceptibility to different antimicrobials agents. Phylogeny of the genotypes on the basis of 18S SSU rDNA and 28S SSU rDNA was also investigated. The isolates of the two genotypes separated into different clades, and no interrelationship was observed among these as shown by phylogenetic analysis. The genotype 1 isolates from cow barn sources were non-pathogenic and may not present any risk of mastitis. We conclude that P. zopfii genotype 2 might play an important role in bovine mastitis in China.