Molecular identification of Prototheca zopfii genotype 2 mastitis isolates and their influence on the milk somatic cell count

Algae from the genus Prototheca are the only plant-like microorganisms which can cause inflammation and alterations in the mammary gland. Prototheca mastitis is usually recognized as a chronic and symptomless disease with reduced milk production and a very high somatic cell count. Molecular identification of Prototheca spp. is helpful for the differentiation of pathogenic from non-pathogenic strains which are probably milk contaminants. Genotype-specific PCR assays, based on the 18S rDNA gene sequences, have recently been developed to differentiate three genotypes of Prototheca zopfii, of which Prototheca zopfii genotype 3 was reclassified in a new species: Prototheca blaschkeae. P. zopfii genotype 2 is characterized as the main causative agent of Prototheca mastitis that leads to significant economic losses in primary milk production. The purpose of this study was to give a molecular characterization of Prototheca strains isolated in cases of subclinical and clinical mastitis, as well as to determine the influence of these pathogenic algae on the milk somatic cell count. After microbiological examination, algae from the genus Prototheca were isolated in pure cultures from 1.8% of all tested milk samples, and all 13 (100%) isolates were determined as Prototheca zopfii genotype 2 by a genotype-specific PCR. This study has provided the first molecular identification of Prototheca zopfii genotype 2 in the Republic of Serbia. In the case of subclinical Prototheca mastitis, the somatic cell count was 4,175,244 +/- 1,233,685/mL of milk. A distinctly higher somatic cell count (P lt 0.05) was found in the quarters infected by Prototheca zopfii genotype 2 than in the quarters infected by Staphylococcus aureus, which is the most common mastitis causative agent worldwide. The results from this study support previous observations that P. zopfii genotype 2 is the main causative agent of Prototheca mastitis which leads to a significant increase in the somatic cell count in the milk