Fate of antibiotic resistance genes (ARGs) in wastewater treatment plant: Preliminary study on identification before and after ultrasonication

This study collected sludge samples from four different sections of a local wastewater treatment plant in Mikkeli, Finland, for antibiotic resistance genes (ARGs) analysis. Here, we examine the seven representative ARGs in sludge, encoding erythromycin (ermB), tetracycline (tetA, tetC, tetQ, tetW) and sulphonamide (sul1) to check abundance before and after ultrasonication. The class 1 integron (intl1) was also observed as an indicator of antibiotic resistance and horizontal gene transmission. The pre-treatment condition included 10 min of ultrasonication (US) for the sludge sample before freeze-drying. The droplet digital PCR system was used to assess the ARGs from the samples, and it was found that ARGs were not effectively eliminated by pre-treatment. After ultrasonication, tetA, tetC and tetQ did not show any variation but tetW showed 20 copies/ng of lower abundance in digested sludge than raw sludge, and a similar abundance was found in dewatered sludge. For MBR sludge, only ermB showed 1000 copies/ng higher abundance compared to the raw sample and surprisingly it did not show the presence of any other types of ARG. This study provides an overview of the appearance of ARGs in regional municipal sludge for further research reflection.