Antibiotic resistance, plasmid-mediated quinolone resistance (PMQR) genes and ampC gene in two typical municipal wastewater treatment plants

Abstract

Antibiotic resistant bacteria and plasmid-mediated quinolone resistance genes and ampC gene were investigated for Escherichia coli isolates from two typical municipal wastewater treatment plants in both dry and wet seasons by using the antibiotic susceptibility test and PCR assay, respectively. The results showed that 98.4% of the isolates (1056) were found resistant to antibiotic(s) tested and 90.6% showed multiple resistances to at least three antibiotics. Tetracycline was found to have the highest resistance frequency (70.8%), followed by ampicillin (65.1%), whereas ceftazidime had the lowest resistance frequency of 9.0%.Moreover, 39.2% of the E. coli isolates were carrying plasmids. intI1 had the highest detection rate in the plasmids (38.1%), followed by qnrS, ampC, qnrB, intI2 and aac(6 0 )-Ib-cr. The disinfection process (UV and chlorination) could significantly reduce the number of bacteria, but percentage of the resistant bacteria, resistance frequency for each antibiotic, MAR index and detection rate of the plasmid-mediated resistance genes were all found increasing in the effluents of biological units. The results of this study showed that a more frequent horizontal gene transfer occurred in the biological units. Wastewater treatment plants were an important medium for the recombination and dissemination of antibiotic resistance genes in the environment. Environmental impactThe wide application of antibiotics can lead to environmental contamination with antibiotic residues and development of bacterial resistance to antibiotics. This has become a global public concern. A variety of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) were widely detected in various environmental media. Effluents from wastewater treatment plants (WWTPs) are suspected to be one of the main anthropogenic sources for ARGs and ARB. Therefore, it is important to understand the removal and dissemination of ARGs and ARB in WWTPs. Plasmids are the major vectors of horizontal gene transfer (HGT). Quinolone resistance genes and ampC gene are two kinds of ARGs contained in the plasmids normally found in many Enterobactericeae isolated from clinical samples. Unfortunately, little is known about their occurrence and characteristics in WWTPs. This study aimed to investigate the antibiotic resistance proles in Escherichia coli isolated from two typical municipal wastewater treatment plants (activated sludge and oxidation ditch processes), to characterize plasmid-mediated quinolone resistance genes, ampC gene and integrons by the polymerase chain reaction (PCR), and to assess the effects of treatment processes on the removal of ARB and ARGs in the WWTPs. The results showed that the treatment processes especially disinfection processes (UV and chlorination) could signicantly reduce the number of bacteria, but increase bacterial resistance in the biological treatment units. The ndings reect the importance of WWTPs as a reservoir of ARB and ARGs, and as a medium for their recombination and dissemination in the en...

Insights into the amplification of bacterial resistance to erythromycin in activated sludge

“…Many studies have investigated and confirmed the prevalence of various kinds of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in the WWTPs of various countries (Reinthaler et al, 2003;Zhang and Zhang, 2011;Bouki et al, 2013;Su et al, 2014).…”

Discharge of swine wastes risks water quality and food safety: Antibiotics and antibiotic resistance genes from swine sources to the receiving environments

“…All qPCR assays were performed on ViiA™ 7 Real-Time PCR System (ABI, USA) using SYBR Green Real Time QPCR Kit (TOYOBO, Japan). The detailed DNA extraction, purification and ARG determination methods can be referred to our previous study (He et al, 2014;Su et al, 2014aSu et al, , 2014b). …”

“…The transfer of antibiotic resistance determinants from human and livestock sources to the environment has gained attention in the scientific community in the past decade (Silbergeld et al, 2008;Storteboom et al, 2010;Wright, 2010), with antibiotic resistance genes (ARGs) considered as emerging environmental contaminants (Pruden et al, 2006). Human wastes are nowadays better treated by centralized wastewater treatment plants than animal wastes with simple treatment systems such as lagoon and digester or even without any treatment before their discharge into the environment (McKinney et al, 2010;Liu et al, 2012;Zhou et al, 2013;He et al, 2014;Su et al, 2014b;Chen et al, 2015). In comparison with other livestock animals (broiler and cattle), antibiotics are commonly used as growth promoter in swine farming (Zhou et al, 2013;Durso and Cook, 2014), thus swine feedlots are of particular concern as potential hot spots for promoting the dissemination of antibiotic resistance (Gotz and Smalla, 1997;Cole et al, 2000;Binh et al, 2008).…”

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