Antimicrobial resistance profile of Vibrio species isolated from marine shrimp farming environments (Litopenaeus vannamei) at Ceará, Brazil

Brazilian shrimp culture industry has a great economic importance mainly to the northeast region. However, the accelerated development of this activity has resulted in the emergency of outbreaks of diseases from farming shrimp, and as a consequence the use of antimicrobial drugs to minimize the potential adverse effect under the shrimp production. The inappropriate use of antibiotics in aquaculture is one of the causes for the high incidence of antimicrobial resistant bacteria isolated from aquatic environments that represent a danger for aquatic organisms and human health. There is little information available on the level of antimicrobial resistance in pathogenic bacteria from shrimp farming environment. Therefore, this study aimed to evaluate the phenotypic resistance profile among Vibrio isolates from hatcheries water samples and from cultivated marine shrimp hepatopancreas (L. vannamei). Antimicrobial susceptibility testing was carried out by a standard disc diffusion method and the minimum inhibitory concentration (MIC) of oxytetracycline (OTC) for resistant Vibrio isolates was determinate by broth dilution method. The results showed a high incidence of resistance to ampicillin (45.2%) and to the tetracycline class (38.7%). Florfenicol and nitrofurantoin were 100% effective against Vibrio isolates. In this study, the OTC-resistant Vibrio spp. showed MIC values of more than 400 mg/L and the presence of seawater did not influence the oxytetracycline bioactivity. The occurrence of antimicrobial multiresistance patterns was observed in 29% of Vibrio isolates. Fifty-five percent of multiresistant isolates of Vibrio lost one or more antibiotic resistance phenotype after procedure to curing of resistance plasmids. The oxytetracycline resistance was the phenotype most often lost among plasmid-cured isolates.