Effects of ciprofloxacin on SML and ULW bacteria

The sea surface microlayer (SML) is a unique habitat for microbes, often impacted by pollutants like heavy metals and pharmaceuticals. This study investigated the effects of various concentrations of ciprofloxacin on bacterial communities in the SML and underlying water from a southern North Sea harbor. Concentrations of 50 and 100 ng/mL influenced bacterial abundances and community dynamics. Notably, significant differences in community composition were observed over time, revealing that both time and ciprofloxacin concentration affect these communities (R² = 67%, P = 0.001). Marine genera such as Planktomarina and Lentibacter persisted in the presence of 100 ng/mL ciprofloxacin, while an unknown Arcobacteraceae increased in abundance, raising concerns about antibiotic-resistant pathogens. Additionally, 97 bacterial cells from 14 genera were enriched at 100 ng/mL ciprofloxacin, with many showing resistance to ciprofloxacin and other antibiotics. This study highlights the need for actions to protect coastal environments from the spread of antibiotic resistance.