Release of antibiotic resistant bacteria and genes in the effluent and biosolids of five wastewater utilities in Michigan
Introduction
The escalating problem of emergence of antibiotic resistant bacteria and their resistant genes is becoming a major global health issue (Levy, 2002, Chee-Sanford et al., 2001). The use of numerous antimicrobial agents as treatments in animal, human, and plant health maintenance, is a worldwide practice providing both desirable and undesirable consequences. Links have been found to exist between antibiotic use and the emergence of antibiotic resistant bacterial pathogens (Aminov et al., 2001, Levy, 2002, Peak et al., 2007, Séveno et al., 2002). Studies have proven increase in antibiotic resistance strains that belong to pathogenic bacteria (Blasco et al., 2008) and over the years, nearly every bacterial pathogen has developed resistance to one or more clinical antibiotics (Todar, 2008).
The general observation published in different studies is that the environmental compartments which are most directly impacted by human or agricultural activities showed higher concentrations of antibiotic resistant bacteria and antibiotic resistant genes (Pruden et al., 2006, Chee-Sanford et al., 2001). Large amounts of antibiotics are released into municipal wastewater due to incomplete metabolism in humans or due to disposal of unused antibiotics (Nagulapally et al., 2009), which finally find their ways into different natural environmental compartments. Antibiotic resistant genes and antibiotic resistant bacteria have been detected in wastewater samples (Zhang et al., 2009a, Zhang et al., 2009b, Auerbach et al., 2007, Brooks et al., 2007, Pruden et al., 2006, Reinthaler et al., 2003). Also, the release of antibiotic resistant organisms through wastewater effluents into streams has been previously reported (Gallert et al., 2005, Iwane et al., 2001). Iwane and their colleagues reported approximately 8% and 6.7% of tetracycline resistant bacteria to be found in the pre- and post-chlorinated samples of a wastewater treatment plant respectively and then close to discharge location in the river water, similar percentages of bacteria were found to be resistant to tetracycline (Iwane et al., 2001). In addition, biosolids samples were reported to contain a high concentration of antibiotic resistant bacteria (Brooks et al., 2007). Also, the role of wastewater treatment plants in reducing the load of antibiotic resistant bacteria present in raw sewage is not well known (Rijal et al., 2009). However, it has been suggested that certain conditions within the wastewater treatment plants might increase the number of antibiotic resistant bacteria during the treatment process (Silva et al., 2006, Reinthaler et al., 2003). To the best of our knowledge, comparisons between different wastewater and biosolids treatment processes have not been studied so far.
The objective of this study was to quantify the release of antibiotic resistant genes (ARGs) and antibiotic resistant bacteria (ARB) in the effluent and biosolids of wastewater treatment plants (WWTPs). This is the first study that surveys the release of ARGs and ARB into the environment through the effluent and biosolids of different wastewater treatment utilities including an MBR (Membrane Biological Reactor), conventional wastewater utilities and multiple sludge treatment processes. This study has attempted to provide comparisons between different wastewater treatment processes and biosolid treatment processes along with the comparison of release loads of ARGs and ARB in the environment through the effluent and biosolids. In this study, samples of raw wastewater, effluent and biosolids were monitored for tetracycline and sulfonamide resistant bacteria, tetracycline resistant genes (tetW and tetO) and sulfonamide resistant gene (SulI) using quantitative polymerase chain reaction (qPCR) assays and conventional heterotrophic plate count methods. Tetracycline and sulfonamide resistance genes (tetW, tetO and SulI) were chosen in this study because tetracycline and sulfonamide are the most commonly used antibiotics in human and veterinary medicine (Boxall et al., 2003, Chopra and Roberts, 2001). In addition, quantitative detection systems already exist for this class of genes (Pei et al., 2006, Aminov et al., 2001). TetW and tetO genes are common in intestinal and rumen environments (Aminov et al., 2001) and have been cited as being promiscuous in their ability to spread among and across populations (Pei et al., 2006, Smith et al., 2004, Billington et al., 2002). SulI gene is also one of the most commonly detected sulfonamide resistant genes in the environment (Pei et al., 2006).
Section snippets
Sample collection
Samples of raw wastewater, effluent prior to disinfection, and final effluent after disinfection were collected from five different WWTPs located in Michigan (U.S.A.). Biosolid samples were also collected from the same treatment plants. Characteristics of the different WWTPs based on wastewater treatment processes, disinfection methods and sludge treatment methods are given in Table 1a, Table 1b. Two or three sampling events were conducted from each of these treatment plants starting from
Overall concentrations of ARGs and ARB in wastewater treatment plants
Concentrations of ARGs and ARB found in this study are presented in Table 3a, Table 3b respectively. Variations among different WWTPs in the raw influent concentration for different genes are expected because of different locations and related human activities. Also wastewater treatment plants receive inflow from a wide variety of sources beyond human population including industrial, hospital and animal waste.
Overall, the trends observed in concentration ranges at different sampling points from
Discussion
This study documents the occurrence of ARGs and ARB at different points in multiple conventional WWTPs and an MBR facility in Michigan. Table 3a, Table 3b illustrate reported ranges of ARGs and ARB presented in different published studies along with a summary of concentration ranges detected in this study. We observed that even though the concentrations of ARGs and ARB in raw wastewater are significantly reduced with wastewater treatment, high concentration is discharged into the effluent.
Conclusions
Wastewater utilities seem to be a potential sources of emerging tetracycline and sulfonamide resistant genes and bacteria in our environment. All raw influent, effluent and biosolid samples analysed in this study were found to contain high concentrations of tetracycline and sulfonamide resistant genes and bacteria. The concentration levels of ARGs and ARB in raw sewage were found be much higher than their respective concentrations in treated effluent. The concentrations of these resistant
Acknowledgements
We would like to thank the managers of all the wastewater treatment plants for providing the samples and information needed for this study. Also, we would like to acknowledge sampling assistance and help provided by Frederick J. Simmons and Arun Kumar.
References (30)
- et al.
Tetracycline resistance genes in activated sludge wastewater treatment plants
Water Res.
(2007) - et al.
Antibiotics and antibiotic resistance in water environments
Curr. Opin. Biotechnol.
(2008) - et al.
Prioritisation of veterinary medicines in the UK environment
Toxicol. Lett.
(2003) - et al.
Effect of river landscape on the sediment concentrations of antibiotics and corresponding antibiotic resistance genes (ARG)
Water Res.
(2006) - et al.
Antibiotic resistance of E. coli in sewage and sludge
Water Res.
(2003) - et al.
Wastewater treatment contributes to selective increase of antibiotic resistance among Acinetobacter spp
Sci. Total Environ.
(2009) - et al.
Molecular ecology of tetracycline resistance: development and validation of primers for detection of tetracycline resistance genes encoding ribosomal protection proteins
Appl. Environ. Microbiol.
(2001) - et al.
Selection of antibiotic-resistant standard plate count bacteria during water treatment
Appl. Environ. Microbiol.
(1982) - et al.
Widespread distribution of a Tet W determinant among tetracycline-resistant isolates of the animal pathogen Arcanobacterium pyogenes
Antibicrob. Agents Chemother.
(2002) - et al.
Multiresistant waterborne pathogens isolated from water reservoirs and cooling systems
J. Appl. Microbiol.
(2008)
Occurrence of antibiotic-resistant bacteria and endotoxin associated with the land application of Biosolids
Can. J. Microbiol.
Occurrence and diversity of tetracycline resistance genes in lagoons and groundwater underlying two swine production facilities
Appl. Environ. Microbiol.
Tetracycline antibiotics: mode of action, applications, molecular biology, and epidemiology of bacterial resistance
Microbiol. Mol. Biol. Rev.
Antibiotic resistance of bacteria in raw and biologically treated sewage and in groundwater below leaking sewers
Appl. Microbiol. Biotechnol.
Possible impact of treated wastewater discharge on incidence of antibiotic resistant bacteria in river water
Water Sci. Technol.
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