Respiratory burst activity of rainbow trout ( Oncorhynchus mykiss) phagocytes is modulated by antimicrobial drugs

Abstract

In vitro and in vivo effects of five different antimicrobial drugs on the chemiluminescence (CL) response of phagocytes isolated from the blood and from the head kidney of rainbow trout ( Oncorhynchus mykiss) were examined. Opsonized zymosan was used to stimulate the respiratory burst utilizing luminol and lucigenin as substrates. The drugs tested were: oxolinic acid (OA), oxytetracycline (OTC), florfenicol (FF) and sulphadiazine in combination with trimethoprim (SDZ/TMP) in ratio 5:1. In the in vitro test, the CL response was measured after a pre-incubation of head kidney and blood phagocytes for 2 and 24 h, with six different concentrations (0.1–100 μg ml −1) of each drug. The lucigenin-enhanced CL response of blood phagocytes was significantly suppressed by OA, OTC and SDZ/TMP at the highest concentration tested, but the luminol-enhanced response was unaffected. The lucigenin-enhanced CL response of head kidney phagocytes was significantly suppressed by SDZ/TMP at concentrations greater than 5 μg ml −1 and by OTC and FF at the highest concentration tested. For the in vivo tests, the fish were fed for 10 days with therapeutic doses of the drugs and the blood and head kidney phagocytes were isolated immediately after the drug exposure. SDZ/TMP stimulated the luminol-enhanced CL response of blood and head kidney phagocytes. FF had a suppressive effect on CL response with luminol and lucigenin on blood phagocytes. OA had a suppressive effect on lucigenin CL response in blood and head kidney phagocytes.