Adenaya, Adenike; Rios-Quintero, Ruben; Lara-Martín, Pablo A; Zumbika, Florence; Wurl, Oliver; Ribas-Ribas, Mariana; Hamprecht, Axel; Brinkhoff, Thorsten: High concentrations of ciprofloxacin reduced bacterial abundance and enrichment in the sea surface microlayer (SML) and underlying water (ULW) and exerted selective pressure on marine bacteria [dataset bundled publication]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.974345 (dataset in review)

The sea surface microlayer (SML) of marine environments is hostile, exposing bacteria to extreme conditions such as temperatures and salinity fluctuations, solar radiation, and the presence of toxic substances such as heavy metals, microplastics, and pharmaceutical compounds. Our study focused on investigating the ecotoxicological effects of varying ciprofloxacin concentrations (0, 10, 50, and 100 ng/ml) on bacterial abundance and enrichment in natural SML and underlying water (ULW) samples obtained from the southern North Sea. In addition, we analyzed the samples for the presence of ciprofloxacin and 25 other antibiotics, including lincomycin, clindamycin, clarithromycin, erythromycin, azithromycin, ofloxacin and novobiocin. Furthermore, we carried out antibiotic susceptibility tests on marine bacterial isolates cultivated in the presence of 100 ng mL ⁻¹, utilizing antibiotics commonly found in their natural habitats. We observed a decrease in bacterial abundance and enrichment in the SML and ULW when exposed to 50 and 100 ng/ml of ciprofloxacin. However, over time, the abundance and enrichment of bacteria increased at these concentrations, indicating resistance. The presence of 100 ng/ml of ciprofloxacin also exerted selective pressure on bacterial members in the SML and ULW, and we cultivated 42 marine and 55 nonmarine bacteria in the presence of 100 ng/ml of ciprofloxacin. Although ciprofloxacin was not detected, we found 11 other antibiotics, particularly in the SML. When we exposed marine bacteria to antibiotics such as novobiocin, ofloxacin, clarithromycin, erythromycin, and clindamycin found in the environment, we observed that some marine bacteria are resistant to these antibiotics. Our findings suggest that resistance in marine bacteria can be acquired through exposure to antibiotics released into coastal water bodies.