No evidence for a relationship between farm or transformation process locations and antibiotic resistance patterns of Pseudomonas population associated with rainbow trout (Oncorhynchus mykiss).

Aims. Study the relationship between antibiotic resistance patterns of Pseudomonas isolated from farmed rainbow trout fillets and farm or transformation process locations. Methods and Results. Pseudomonas strains were isolated from rainbow trout sampled in two differently located farms and filleted in laboratory or in a processing factory. One hundred and twenty-five isolates were confirmed as belonging to Pseudomonas using CFC selective media, Gram staining, oxidase test and quantitative polymerase chain reaction methods. Fifty-one isolates from separate fish fillets were further identified using MALDI-TOF mass spectrometry, and the minimal inhibitory concentrations (MIC) of 11 antibiotics were also determined by microdilution method. Most of the isolates belonged to the Pseudomonas fluorescens group (94.1%), and no relationship was established between antibiotic resistance patterns and sampling locations (farms or filleting areas). Multiple resistance isolates with high MIC values (from 64 µg ml^-1 to more than 1024 µg ml^-1) were identified. Conclusions....