engleski

Predominance of CTX-M-15 encoded by conjugative IncFIB -type plasmids among Gram-negative opportunistic pathogens in coastal marine waters in Croatia

In a recent decade, the evolving threat of antimicrobial resistance has imposed as a global and worrisome problem from medical, economic and also ecological point of view. Detection and prompt identification of resistance traits in bacteria persisting in a specific environment have imposed as key steps in evaluating the potential of a certain environment to represent a reservoir of antibiotic resistance. In this regard, the aquatic ecosystems highly impacted by human activities have been recognized as hot- spots that significantly contribute to dissemination of resistant strains and associated genes, and even to the proliferation of novel resistance mechanisms and pathogens. The Kaštela Bay, a semi-enclosed bay in the central part of the eastern Adriatic coast, has a highly urbanized and industrialized coastal belt and receives extensive urban and industrial wastewater discharges, making it a good model for studying the role of polluted marine environment in dissemination of pathogenic bacteria resistant to antibiotics. During a 4-year period, over 2600 isolates were recovered from seawater and fauna and determined their antibiotic resistance patterns. Characterization of resistance genes, with special focus on extended spectrum-β- lactamases (ESBLs) were performed by PCR, sequencing, conjugation, transformation and Southern blot hybridization. TEM, SHV and CTX-M β-lactamases were identified in a significant percentage of Enterobacteriaceae, Aeromonas, Pseudomonas, Burkholderia, Stenotrophomonas and Vibrio isolates. The predominant ESBL was the CTX-M-15 and was identified in eight species of Enterobacteriaceae, Aeromonas spp., Stenotrophomonas maltophilia, Acinetobacter spp. and Vibrio spp. Interestingly, all transferable plasmids carrying the blaCTX-M-15 belonged to the IncFIB incompatibility group, indicating the importance of the role of this specific type of resistance plasmids in a possible horizontal transfer of blaCTX-M-15 among phylogenetically distant bacterial species and genera, ongoing in this particular marine environment. In addition, isolate fingerprinting revealed that marine E. coli isolates were closely related to CTX-M- producing strains from a regional university hospital, indicating that marine beach waters are reservoirs of ESBL-producing Enterobacteriaceae with further potential to act as mediators in gene flow between marine coastal areas and clinical settings.

Antibiotic resistance ; Gram-negative bacteria ; CTX-M-15 ; beta-lactamase ; plasmids ; marine environment

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