Microbial Response to Biosolids-Borne Ciprofloxacin (CIP) and Azithromycin (AZ).

Microbes can be highly sensitive to trace organic compounds (TOrCs), but the fate and microbial bioavailability of biosolids-borne TOrCs is not well understood. Ciprofloxacin (CIP) and azithromycin (AZ) are two such ionic TOrCs commonly present in biosolids, owing to their use to treat a number of bacterial infections in humans. A 90-day microbial incubation study was conducted to assess microbial response to varying environmentally relevant concentrations of biosolids-borne CIP and AZ. We studied changes in microbial respiration and employed molecular techniques (RNA analysis) to study various microbial responses involved in N and P cycles and antibiotic resistance development over time. Using ³H-labeled compounds, we assessed CIP and AZ bioavailability to microorganisms and correlated chemical extractability (potential bioaccessibility) and degradation to microbial responses in biosolids and amended soil media. Positive effects of biosolids amendment out weigh adverse TOrC effects from an agronomic viewpoint. However, inhibition of gene expressions of some microbes (at least initially) and expression of antibiotic resistance genes warrant longer term studies to fully assess potential for a biosolids-borne TOrC’s impacts on microbes and corresponding resistance genes.