Abstract
Considering high concentrations of multidrug-resistant bacteria and antibiotic resistance genes (ARGs) in wastewater, agricultural reuse of treated wastewater may be a public health threat due to ARG dissemination in different environmental compartments, including soil and edible parts of crops. We investigated the presence of antibiotic-resistant Escherichia coli as an indicator bacterium from secondary treated wastewater (STWW), water- or wastewater-irrigated soil and crop samples. ARGs including blaCTX-m-32, blaOXA-23, tet-W, sul1, cml-A, erm-B, along with intI1 gene in E. coli isolates were detected via molecular methods. The most prevalent ARGs in 78 E. coli isolates were sul1 (42%), followed by blaCTX-m-32 (19%), and erm-B (17%). IntI1 as a class 1 integrons gene was detected in 46% of the isolates. Cml-A was detected in STWW isolates but no E. coli isolate from wastewater-irrigated soil and crop samples contained this gene. The results also showed no detection of E. coli in water-irrigated soil and crop samples. Statistical analysis showed a correlation between sul1 and cml-A with intI1. The results suggest that agricultural reuse of wastewater may contribute to the transmission of antibiotic-resistant bacteria to soil and crop. Further research is needed to determine the potential risk of ARB associated with the consumption of wastewater-irrigated crops.
Highlights
In recent decades, the excessive use of antibiotics as therapeutic drugs in humans, animals, and plants has caused selective pressure on bacterial populations, leading to the dissemination of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in the environment (Osińska et al 2017; Yuan et al 2020)
Analysis of ARGs showed the presence of sul1, erm-B, blaCTX-m-32, cml-A, and intI1 genes in E. coli isolates with the highest frequency of detection for sul1
The results of this study revealed a small percentage of Multidrug resistance (MDR) (9%) E. coli compared with other studies (Osińska et al 2017; Aristizábal-Hoyos et al 2019)
Summary
The excessive use of antibiotics as therapeutic drugs in humans, animals, and plants has caused selective pressure on bacterial populations, leading to the dissemination of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in the environment (Osińska et al 2017; Yuan et al 2020). Considering high concentrations of ARB and ARGs in the effluent of WWTPs, agricultural reuse of secondary treated wastewater (STWW) could considerably spread antibiotics, ARB and ARGs into the environment (Cerqueira et al 2019a; Kumar et al 2020) This may lead to an elevated resistance level in microbiome of soil and crops The common types of integrons which confer resistance to antibiotics including β-lactam antibiotics, chloramphenicol, sulfonamides, aminoglycoside, spectinomycin and others (Su et al 2012) are class 1 integrons This type of integrons are widely distributed in ARB, especially in Gramnegative bacteria (Osińska et al 2017). Antibiotic resistance was determined by detecting six ARGs, including blaCTX-m-32, blaOXA-23, tet-W, sul, cml-A, erm-B as well as intI1 gene (a key component of class 1 integrons) as a marker of anthropogenic pollution in E. coli isolates
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