General Soil Properties Modulate Bacterial Community Tolerance to Clarithromycin in Laboratory-Spiked Agricultural Soils

Clarithromycin is a widely prescribed macrolide antibiotic that can enter soils using sewage treatment plant effluents, where it is frequently detected. Because it could exert selective pressure on soil microbes, this study examined whether bacterial communities in 12 agricultural soils developed tolerance to clarithromycin after 42 days of exposure to different clarithromycin concentrations (7.8 mg kg−1–2000 mg kg−1). Results showed that tolerance increased in a clear dose-dependent manner and was significantly higher than in control soils at concentrations of 31.3 mg kg−1 and above. Soil characteristics also shaped the response. At lower clarithromycin doses, tolerance was restricted in those soils with higher values of eCEC, clay content, organic carbon, and C/N ratio. At higher doses, tolerance increased with pH, likely due to increased clarithromycin bioavailability. This study provides evidence of the impact of clarithromycin on soil microbiota and suggests that contamination by this antibiotic may promote the development of bacterial tolerance. Future studies should be carried out to further clarify the factors that influence the development of tolerance and also to determine the possible spread of this resistance in the environment.