The total abundance of resistance genes was three times higher in sludge from the treatment plant receiving wastewater from pharmaceutical production than in sludge from a treatment plant in Zagreb, treating typical municipal sewage.
Researchers at CARe and the Ruđer Bošković Institute in Croatia have published a study in Water Research, in which they used metagenomics to investigate antibiotic resistance genes in sludge from a treatment plant in Croatia receiving wastewater from production of the macrolide antibiotic azithromycin. The team found that the total abundance of resistance genes was three times higher in sludge from the treatment plant receiving wastewater from pharmaceutical production than in sludge from a treatment plant in Zagreb, treating typical municipal sewage. Surprisingly, macrolide resistance genes were not enriched. This suggests that at high concentrations of antibiotics, taxonomic shifts towards intrinsically resistant species or strains harboring chromosomal resistance mutations may be favored over acquisition of mobile resistance genes. The study highlights the need for regulatory action also within Europe to avoid release of antibiotics into the environment.