The Occurrence of Integrase Genes in Different Stages of Wastewater Treatment

The uncontrolled use of antibiotics and the release of drug residuals into the environment contribute to antibiotic resistance and constitute a serious public health threat. The spread of antibiotic resistance can be attributed mainly to the huge amounts of bacteria harboring the antibiotic resistance genes (ARGs) which are released into the environment with the treated wastewater. The molecular mechanisms of antibiotic resistance, in which the mobile genetic elements (MGEs) such as plasmids. transposons. bacteriophages and integrons associated with the transfer of ARGs play the main role. should be broadly investigated to develop effective methods for addressing this problem. This study focused mainly on integrons which: (i) are the simple elements involved in the mobility of gene cassettes, (ii) have a common structure, (iii) can be associated with other MGEs, and (iv) are particularly efficient in trapping ARGs. The aim of the study was to estimate the efficiency of different stages of the wastewater treatment process in removing class 1, 2 and 3 integrase genes in two wastewater treatment plants (WWTPs) in Poland and to investigate the presence of these genes in river water upstream and downstream from the effluent discharge point. The presence of intI1, intI2 and intI3 genes was analysed by means of standard PCR with specific primers and a thermal cycling profiles. The samples of wastewater and sludge were collected from two WWTPs located in the Polish regions of (a) Warmia and Maury. and (b) Silesia. The samples of river water were also collected upstream and downstream from the examined WWTPs. In the selected WWTPs, wastewater is treated through the activated sludge process with various modifications. The presence of intI1. intI2 and intI3 genes in different stages of wastewater treatment was characterized by a similar pattern. The results of this study indicate that WWTPs arc not highly effective in removing the integrase genes from all three integron classes. The study revealed somewhat unexpected results, which indicate that the recently discontinued monitoring of the intI3 gene in the wastewater treatment process should be reinstated. The existing wastewater treatment systems should be improved and modified to effectively eliminate the integrase genes from wastewater and prevent contamination of the surface water.