International maritime organization, we may have a problem - ballast water treatment triggers global concerns with antimicrobial resistant bacteria.

Vessels sailing worldwide need to treat ballast water to inactivate organisms to comply with the Ballast Water Management Convention. We analysed the phenotypic resistance of isolated unidentified bacteria to antimicrobial substances in the uptake water before treatment and the discharged water after treatment on a vessel in operation with a certified UV based ballast water management system (BWMS). We isolated Escherichia coli on selective media and genotyped the identified isolates. All isolates were categorized into clonal and phylogenetic groups based on Polymerase Chain Reaction (PCR) methods. We examined the presence of Plasmid-mediated Quinolone Resistance (PMQR) genes, betalactamases, adhesins, autotransporters, genes encoding iron uptake proteins, genes associated with immune system evasion, and genotoxins. For all non-clonal isolates, we tested their sensitivity to antimicrobial substances. Resistance to cefotaxime increased after treatment in both intrinsic resistance and E. coli isolates. PCR analyses showed a decrease in the occurrence of qnrS and ompTAPEC genes in the discharged water, and an increase in qnrB, kpsMTII, blaTEM, fyuA, and usp genes. The results of the disk diffusion method indicated an increase in resistance to ampicillin, ceftazidime, and the highest increase occurred in resistance to cefotaxime. The number of multi-drug resistant isolates decreased substantially in the discharged water. BWMS effectively eliminate plankton, while UV water treatment causes different negative changes in bacteria, introducing new threats to human health (microbiome to accumulate resistance genes) and aquaculture (increase diversity and volume of antibiotics used, lower seafood production), hence opening a new issue in global discharges of ballast water.