Antibiotic Resistance Properties among Pseudomonas spp. Associated with Salmon Processing Environments

Continuous monitoring of antimicrobial resistance in bacteria along the food chain is crucial for the assessment of human health risks. Uncritical use of antibiotics in farming over years can be one of the main reasons for increased antibiotic resistance in bacteria. In this study, we aimed to classify 222 presumptive Pseudomonas isolates originating from a salmon processing environment, and to examine the phenotypic and genotypic antibiotic resistance profiles of these isolates. Of all the analyzed isolates 68% belonged to Pseudomonas, and the most abundant species were Pseudomonas fluorescens, Pseudomonas azotoformans, Pseudomonas gessardii, Pseudomonas libanesis, Pseudomonas lundensis, Pseudomonas cedrina and Pseudomonas extremaustralis based on sequencing of the rpoD gene. As many as 27% of Pseudomonas isolates could not be classified to species level. Phenotypic susceptibility analysis by disc diffusion method revealed a high level of resistance towards the antibiotics ampicillin, amoxicillin, cefotaxime, ceftriaxone, imipenem, and the fish farming relevant antibiotics florfenicol and oxolinic acid among the Pseudomonas isolates. Whole genome sequencing and subsequent analysis of AMR determinants by ResFinder and CARD revealed that no isolates harbored any acquired resistance determinants, but all isolates carried variants of genes known from P. aeruginosa to be involved in multidrug efflux pump systems.