Microbiological Quality Assessment of Water and Fish from Karst Rivers of the Southeast Black Sea Basin (Croatia), and Antimicrobial Susceptibility of Aeromonas Isolates


Karst rivers are of great interest for commercial fishing and aquaculture, yet they are quite vulnerable aquatic environments because the permeable karst rocks do not effectively filter out contaminants. To understand the current state of karst rivers water quality, we analysed the physico-chemical and microbiological parameters, focusing on antibiotic pollution and the emergence of antibiotic-resistant microbes of three such rivers in Croatia. Water quality varied between classes I and II across sampling sites, and the numbers of total coliforms, enterococci and heterotrophic bacteria varied substantially among sites. Swabs from fish gills, spleen, liver and kidneys were cultured and 94 isolates identified by MALDI-TOF mass spectrometry. The predominant genus was Aeromonas (42.5% of all identified isolates), known for its adaptability to polluted environments and its frequent association with antibiotic resistance. Of the selected Aeromonas isolates known as most pathogenic, half were resistant to at least three antibiotic categories. The Enterobacteriaceae family was represented by the greatest number of genera, most of which are pathogenic for humans and animals and are spoilage bacteria for fish. The results of this study highlight the extent of antibiotic contamination in aquatic environments and the increasing threat of pathogenic and spoilage bacteria in traditionally high-quality karst rivers.

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Data Availability

The authors confirm that the data supporting the findings of this study are available within the article. Any additional data requirements are available on request from the corresponding author.


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This research was supported by the projects funded by the Ministry of Agriculture Republic of Croatia and by the Croatian Science Foundation (IP-2014–09-3494: Aquatic microbial ecology as an indicator of the health status of the environment – AQUAHEALTH). We are thankful to Damir Valić, PhD for his contribution in the sampling process and for valuable insights to the paper. We are thankful to Creaducate Consulting GmbH for English language editing and proofreading of our manuscript.


“Monitoring of fish stock in fishing area of the river Kupa in 2016”, Ministry of Agriculture—Directorate of Fisheries Republic of Croatia and AQUAHEALTH (IP-2014–09-3494), Croatian Science Foundation.

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Correspondence to Damir Kapetanović.

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Ethical Approval

All applicable institutional, national and international guidelines for the welfare and use of animals were followed. Electrofishing and fish collection for Freshwater Fisheries Monitoring Program in 2016 was made with the authorization of the Ministry of Agriculture of the Republic of Croatia (Class: UP324-01/16–01/134, Reg. No: 525–13/0515–16-2 of August 3, 2016), based on the Contract concluded with Ministry of Agriculture (Class: 406–01/16–01/42, Reg. No: 525–05 / 03836–16-14 of June 30, 2016). We consulted extensively with the Bioethics Committee of the Ruđer Bošković Institute who determined that Freshwater Fisheries Monitoring Program in 2016 did not need ethical approval, as the fish were euthanized prior to commencement of the organ sampling. Project AQUAHALTH was approved by the Bioethics Committee of the Ministry of Agriculture of the Republic of Croatia Directorate for Veterinary and Food Safety (Class: UP/I-322–01/15–01/71; Reg. No: 525–10/0255–15-3 of October 6, 2015).

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Kolda, A., Mujakić, I., Perić, L. et al. Microbiological Quality Assessment of Water and Fish from Karst Rivers of the Southeast Black Sea Basin (Croatia), and Antimicrobial Susceptibility of Aeromonas Isolates. Curr Microbiol (2020). https://doi.org/10.1007/s00284-020-02081-5

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