Multicentre Etest evaluation of in vitro activity of conventional antifungal drugs against European bovine mastitis Prototheca spp. isolates.

OBJECTIVES: Bovine mammary protothecosis is a serious pathology that entails high economic losses in the dairy industry. The disease, the frequency of which has recently been increasing worldwide, is caused by unicellular, achlorophyllous, yeast-like algae of two species: Prototheca zopfii and Prototheca blaschkeae. The objective of this study was to investigate the in vitro activity of a panel of conventional antifungal drugs against Prototheca spp. isolates. METHODS: A total of 144 P. zopfii genotype 2 and P. blaschkeae strains isolated from milk of mastitic cows were subjected to drug susceptibility testing by Etest methodology. RESULTS: Five out of ten antifungal drugs tested exhibited no activity against Prototheca spp. isolates. The best activity against Prototheca spp. was demonstrated by amphotericin B (MIC90 of 1.5 mg/L). The MICs differed significantly (P < 0.01) between P. zopfii genotype 2 and P. blaschkeae, with the latter species being more susceptible to amphotericin B and azoles. Marked differences (P < 0.05) in azole and amphotericin B activities were noted among Prototheca spp. isolates originating from different European countries. Based on the correlation coefficients, a considerable cross-interaction was found among MICs of azoles and between MICs of azoles and amphotericin B for Prototheca spp. (P < 0.03). CONCLUSIONS: This study represents the largest, cross-European evaluation of antifungal activity against Prototheca spp. to date. The activity of amphotericin B against Prototheca spp. validates its potential use as a therapeutic agent against bovine protothecosis. For laboratory testing of drug activity against Prototheca spp., the Etest method is encouraged, due to its technical simplicity, rapidity and high intra- and inter-laboratory reproducibility.

Large-scale screening of the in vitro susceptibility of Prototheca zopfii towards polyene antibiotics.

A large scale screening of the in vitro susceptibility of 105 strains of Prototheca zopfii to a panel of polyene antibiotics (amphotericin B, nystatin, primaricin and filipin) was conducted. Strains studied were isolated from dairy-associated environments in five different localities. Groups 1-4 included strains recovered from four separate regions of Italy, while group 5 included isolates from Belgium. Amphotericin B and primaricin exhibited the highest activity, with th MIC90 ranging from 4 and 8 microg/ml, respectively. On the other hand, the MIC90 of nystatin and filipin were from two to four times higher. Two strains were resistant to all four polyenes tested. The above results are compared with those in the literature and the importance of carrying out large-scale screening surveys to assess polyene susceptibility patterns within the species P. zopfii is discussed.