Abstract
This paper presents the spatio-temporal distribution of faecal indicator bacteria (FIB) in the river section subject to anthropogenic stress and describes spread patterns of antibiotic resistance in the studied bacterial groups. The analysis involved 58 strains of Escherichia coli and 61 strains of enterococci. Antibiotic resistance profiles were prepared in accordance with the recommendations of the European Committee on Antimicrobial Susceptibility Testing (EUCAST). The results indicated a correlation between the location of a sampling site and the concentration of faecal bacteria. The highest average concentrations were recorded at the site located in the city centre, where the river is used mainly for recreation. Antibiotic resistance profiles showed that Escherichia coli had 100% sensitivity to tigecycline, levofloxacin and imipenem. The highest percentaage of strains (17%) were resistant to piperacillin. Enterococci were 100% sensitive to levofloxacin. No strains were vancomycin-resistant (VRE). The highest percentage of strains was resistant to imipenem (23%), and the lowest, to ampicillin (2%). The spatio-temporal distribution of antibiotic-resistant strains (ARS) indicated a high concentration of drug-resistant Escherichia coli (47%) in the summer season at the sampling site located in the last part of the river. At the same time, drug resistance in enterococci increased along the river course and was considerably higher in spring. There were no significant relationships between physico-chemical parameters of water and the levels of faecal bacteria. On the other hand, strong relationships were observed between the percentage of strains showing resistance to the applied antibiotics and physico-chemical and biological parameters of water. The percentage of antibiotic resistant strains of Escherichia coli was negatively correlated with dissolved oxygen concentration (r = − 0.9; p < 0.001) and BOD5 (r = − 0.85; p < 0.05). The percentage of antibiotic resistant strains of enterococci was most strongly correlated with water pH (r = − 0.92; p < 0.001).
Highlights
Since the beginning of human settlement, rivers have played a key role in the development of towns and cities, ensuring the progress of civilization
The analysis of the spatial distribution of faecal bacteria indicated that both Escherichia coli and enterococci were the least abundant at the sampling site located at the beginning of the studied section of the river
Maximum concentrations were recorded in rainy autumn months at the sampling site affected by anthropopressure to the highest degree, which corresponds with the results of other studies
Summary
Since the beginning of human settlement, rivers have played a key role in the development of towns and cities, ensuring the progress of civilization. Aquatic ecosystems in urban areas are used mainly for recreation, contirbuting to the development of tourism [2]. As a result, they are often exposed to physical, chemical and biological contamination [3]. Surface waters, antibiotics are found at concentrations that significantly affect the activity of bacterial genes, leading, among others, to their increased mutation frequency [9]. This carries the risk of transferring resistance genes between pathogenic and non-pathogenic bacterial cells, and poses a direct danger to people [10]. Bacteria displaying resistance to most available antibiotics were already found in anthropogenically impacted environments more than a decade ago [11]
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