Dynamic exchange of bacteria and carbapenem resistance genes between sewer biofilms and wastewater

ABSTRACT A sewer pipe with flowing wastewater and associated bacteria in the flowing wastewater, biofilm attached to the sewer pipe, and the periodically wetted biofilm surface on the pipe are shown. overarching research finding that 'Sewer biofilms influence wastewater ecology' is written. Three research questions are described, including question 1 of 'Time to establish complex biofilm?', question 2 of 'Detachment rate from biofilm to wastewater?' and question 3 of 'Mass balance on detachment and re-attachement.' Sewer biofilms exchange bacteria and antibiotic-resistance genes with the overlying wastewater. Using inline biofilm reactors, movement of bacteria, 16S rRNA, and carbapenemase genes (blaKPC, blaVIM, blaNDM, blaOXA-48-like, and blaIMP) between wastewater and sewer biofilms was studied. Over five experiments, biofilm establishment on polyvinyl chloride (PVC), changes in bacterial community after exposure to raw and treated wastewater, biofilm absorption of bacteria, and release of bacteria and genes were investigated. In laboratory studies, established biofilms with carbapenem-resistant bacteria contributed more bacteria to wastewater than to downstream biofilms under realistic shear. In field studies, established biofilms acquired target carbapenem-resistant bacteria and genes from wastewater within hours, and concentrations stabilized between 2 and 15 days and then varied by <0.5 most probable number/cm2 or 0.5 log gene copies (GC)/cm2. Metagenomic profiles of biofilm bacteria changed over 21 days. Established biofilms with antibiotic-resistant bacteria and genes exposed to tertiary-treated wastewater without target carbapenemase genes or meropenem antibiotics retained resistant genes and bacteria over 9 days dropping < 1 log GC/cm2. Results show that sewer biofilms contribute to wastewater antibiotic-resistance gene signals by absorbing and later releasing bacteria and genes. Sewer biofilm dynamics evaluation is essential for accurate interpretation of bacterial concentrations in wastewater-based epidemiology studies.