Class 1 Integrons and the Antiseptic Resistance Gene (qacEΔ1) in Municipal and Swine Slaughterhouse Wastewater Treatment Plants and Wastewater-Associated Methicillin-Resistant Staphylococcus aureus.

Min Wan,Chin Chou

doi:10.3390/ijerph120606249

Abstract

Class 1 integrons are mobile gene elements (MGEs) containing qacEΔ1 that are resistant to quaternary ammonium compound (QAC) disinfectants. This study compared the abundances of class 1 integrons and antiseptic resistance genes in municipal (M) and swine slaughterhouse (S) wastewater treatment plants (WWTPs) and investigated the presence of class 1 integrons and antiseptic resistance genes in methicillin-resistant Staphylococcus aureus (MRSA) isolated from wastewater samples. The abundances of intI1 and qacEΔ1 genes in 96 wastewater samples were quantified using real-time quantitative polymerase chain reaction (real-time qPCR), and 113 MRSA isolates recovered from the wastewater samples were detected class 1 integrons and linked antiseptic resistance genes (qacEΔ1), and minimum inhibitory concentrations (MICs) for QAC antiseptics. The intI1 and qacEΔ1 genes were detected in all the wastewater samples, and they were more abundant in S-WWTP samples than in M-WWTP samples. A higher percentage of MRSA isolates carried qacEΔ1 in MRSA from swine wastewater samples (62.8%) than in municipal MRSA (3.7%). All the MRSA isolates showed high MICs for antiseptic agents. This study provides important evidence regarding the abundances of intI1 and qacEΔ1 genes in municipal and swine slaughterhouse wastewater, and antiseptic-resistant MRSA strains were detected in swine slaughterhouse wastewater.

Highlights

Antibiotic-resistant bacteria (ARB) have been found in aquatic environments, including surface water and groundwater [1,2]
Wastewater samples taken at sampling site M-A were the incoming influent wastewater at the municipal wastewater treatment plant (M-WWTP); samples taken at sampling site M-B and M-C were wastewater before and after solid removal during primary treatment, the hydraulic retention time (HRT) between both is 1.1 h; samples taken at sampling site M–D were after secondary treatment for activated sludge process, the HRT is 4.8 h; samples M–E were taken from final clarification site, the HRT is 3.8 h, and samples M-F were the effluent water taken after chlorination treatment with HRT of 25.5 min
slaughterhouse wastewater treatment plant (S-WWTP) were higher than those in the effluent of the M-WWTP by one order of magnitude. These results suggested that the continuous discharge of municipal wastewater and swine slaughterhouse wastewater may release intI1 and qacEΔ1 into natural water environments, implying that

Summary

Introduction

Antibiotic-resistant bacteria (ARB) have been found in aquatic environments, including surface water and groundwater [1,2]. Wastewater has been reported to be a significant hotspot for the development and dissemination of ARB and antibiotic-resistant genes (ARGs) through horizontal gene transfer [3]. Integrons are mobile DNA elements that are frequently associated with antibiotic resistance [8]. Integrons consist of two conserved segments (CSs) usually separated by a variable region that includes mobile cassettes with antibiotic resistance genes [8]. In class 1 integrons, the 5’-CS harbors the class 1 integrase gene (intI1) and an attachment site (attI) that can capture and express resistant genes [8,9]

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