In vitro efficacy of new antiprotozoals against Philasterides dicentrarchi (Ciliophora, Scuticociliatida)

Philasterides dicentrarchi is a histiophagous ciliate that causes severe losses in turbot and sea bass farming. This study investigated the in vitro efficacy against P. dicentrarchi of 85 newly synthesized compounds and 12 commercial compounds, of which 2 are fluoroquinolones (nor- floxacine and lomefloxacine) with known antibacterial activity. Seventeen of the newly synthesized compounds (2 naphthyridines, 2 pyridothienodiazines and 13 pyridothienotriazines) and the fluoro- quinolone norfloxacin showed good activity. The most promising compound was the pyridothienotri- azine 12k, with activity similar to that of the salicylanilides niclosamide and oxiclozanide (MLC 0.8 mg l -1 in PBS, 1.5 mg l -1 in seawater; MLC = minimum 24 h lethal concentration).