Aeromonas hydrophila in Rhamdia quelen: macroscopIc and microscopIc aspect of the lesions and antibiotic resistence profiles

Abstract

With the intensification of fish culture in Rio Grande do Sul, the incidence and severity of pathologies increased significantly; fish raised under inappropriate management conditions are prone to stress related pathologies, such as that caused by Aeromonas hydrophila. Herein, the isolation, antibiotic sensibility and macroscopic and microscopic lesions caused by A. hydrophila are described. The identification of A. hydrophila was confirmed following inoculation on blood agar and biochemical assays. Macroscopic lesions were initially observed as ulcers in the caudal peduncle that became disseminated through the body and barbs, exposing muscle tissue. Histopathological lesions were characterized by degeneration, necrosis, hyperplasia, mononuclear cell infiltration and the presence of bacteria colonies. All samples of A. hydrophila were susceptible to chloramphenicol, polymyxin B, kanamycin, sulfonamides and neomycin; 81.25% of the samples were susceptible to doxycyclin and 18.75% had intermediate susceptibility. Cefoxitin was effective against 75% of the samples, but 18.75% of the samples had intermediate susceptibility and 6.25% were resistant. The susceptibility to erythromycin observed among 50% of the samples, but 31.25% and 18.75% of the samples has intermediate susceptibility or were completely resistant, respectively. Thus, to know the resistance profiles of the bacteria and to prescribe an effective treatment when recommended, it is necessary to perform antibiotic susceptibility test to each outbreak of this disease.