Abstract
The aim of this study was to determine the effect of trout aquaculture effluents on the Drwęca River. The count of opportunistic pathogen Pseudomonas fluorescens (OPPF) in the total Pseudomonas fluorescens population (TPFP) were determined by plating on King B medium and fluorescence in situ hybridization. The resistance of OPPF strains to 12 antibiotics and two disinfectants was evaluated. Significant differences (p ≤ 0.05) in OPPF counts were found between seven sampling sites. OPPF counts were highest in samples collected directly downstream from three fish farms. More than 50% of these isolates demonstrated multiple-drug resistance to ampicillin, mezlocillin, cefotaxime, norfloxacin, tetracycline and two disinfectants (Steridial and chloramine T). Of these, 52% were resistant to high doses of cefotaxime and norfloxacin (MIC ≥ 256 µg·mL−1), and 65% were resistant to the maximum doses of Steridial (MIC Ste ≥ 25 mL·m−3) and chloramine T (MIC Chlor ≥ 20 mg·L−1). All OPPF sampled upstream from the farms were sensitive to low concentrations of CTX (cefotaxime) and NOR (norfloxacin) (MIC ≤ 2 µg·mL−1), Steridial (MIC Ste ≤ 5 mL·m−3) and chloramine T (MIC Chlor ≤ 2.5 mg·L−1). Agglomerative clustering revealed two clusters: strains from samples collected upstream and downstream from trout farms. The results indicate that aquaculture effluents significantly affect the prevalence of biocides resistant OPPF along the river continuum.
Highlights
Pseudomonas fluorescens bacteria are widespread in natural and anthropogenically altered water environments
Most Opportunistic Pathogens P. fluorescens (OPPF) strains isolated from water samples collected downstream from fish farms were resistant to the recommended doses of Steridial (5–25 mL·m−3 ) and chloramine T
The results of this study indicate that aquaculture effluents exert a significant effect on the concentrations of OPPF and their sensitivity to biocides in the upper course of the Drweca River, which is a nature and ichthyological reserve
Summary
Pseudomonas fluorescens bacteria are widespread in natural and anthropogenically altered water environments. They form the natural microbiota of ecosystems in which they play an important role in the decomposition of organic matter, circulation of elements and self-purification processes [1,2]. Some P. fluorescens strains show hemolytic activity and are classified as opportunistic P. fluorescens pathogens These strains could be an important causative agent of epizootic diseases in fish, other wild animals, livestock and, humans [3,4,5]. Higher concentrations of potentially pathogenic strains in water bodies increases the risk of infection for aquatic organisms and contributes to their spread in aquatic ecosystems, and among humans, livestock and wildlife [6,7].
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