Discharge of Pasteurella piscicida Cells from Experimentally Infected Yellowtail

Abstract

Yellowtail (Seriola quinqueradiata) weighing 40-92g were experimentally infected with an oxolinic acid (OA) resistant strain of Pasteurella piscicida, and then the discharge of the bacterial cells from the fish was determined by using trypticase-soy agar containing OA. The infected fish began to shed P.piscicida cells one or two days before death. The number of cells shed from dead fish reached 10⁷-10⁹CFU/fish·10min, and the same level of bacterial shedding was kept for about 5 days after death. It was also confirmed that the released bacteria (2.4×10³CFU/ml) had high infectivity to yellowtail.