In vitro and in vivo effects of antimicrobial agents on viability of Cryptobia salmositica (Sarcomastigophora: Kinetoplastida)

Abstract

C. salmositica from blood of infected rainbow trout (blood forms) or cultures (culture forms) were incubated in vitro with a combination of penicillin, streptomycin and amphotericin B (antimicrobial agents, AM). Trypan blue dye exclusion test showed that slender forms did not take up the dye whereas many round forms became coloured as incubation proceeded. Culture forms were more susceptible to AM than blood forms. Washing the blood forms prior to incubation with AM increased their susceptibility, but they were still more resistant than unwashed or washed culture forms. Trypan blue had a protective effect on viability of both blood and culture forms exposed to AM. Parasites exposed to AM were still infective when inoculated into rainbow trout. Injection of AM into fish infected with blood or culture forms did not affect the parasitaemias. Although C. salmositica and trypanosomes are phylogenetically related, AM did not affect trypanosomes (mammalian and piscine).