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Keywords
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antibiotic resistance, Escherichia coli, heterotrophic bacteria, urban wastewater,
β-lactamase gene
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Abstract
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Municipal water resource recovery facilities (WRRFs) are important sources of
antibiotic-resistant bacteria and genes (ARB and ARGs). In this study,
antibiotic-resistant total heterotrophic bacteria (THBR) counts (CFU/ml)
cultivated from influent, effluent of activated sludge process, and outflow of
disinfection unit of an urban WRRF were investigated for the presence of 16, 32,
64, and 128 μg/ml of nine antibiotics. The isolates of Pseudomonas spp.,
Acinetobacter spp., and Escherichia coli obtained from effluent of activated sludge
process were subjected for molecular identification by detecting the 16S rRNA
gene sequences. Additionally, using the polymerase chain reaction method
(PCR), the isolates were investigated for the presence of blaSHV, blaTEM,
blaCTX-M, blaVIM, sul1, and qnrS genes. According to the results, the abundance
of THBR counts was not significantly reduced by the biological treatment except
for cefixime and sulfamethoxazole; it also increased for some antibiotics after
disinfection unit. The average removal efficiency of THBR resistant to ciprofloxacin,
sulfamethoxazole, and ceftazidime were 7.9 ± 1.7%, 41.8 ± 2.1%, and
14.4 ± 6.2%, respectively. Also, all the tested isolates were resistant to at least
four antibiotics. For all antibiotics, the resistance ratio (THBR/THB) significantly
increased in the effluent and after chlorination unit. Among 12 resistant isolates,
blaTEM and sul1 genes were the most frequently detected ones involved in 92%
and 83% of the isolates, respectively. Both blaTEM and sul1 genes were found in
100% of E. coli, and 83% and 67% of Pseudomonas spp. isolates, respectively. Further
efforts are necessary to limit the transmission of ARB and ARGs from
WRRFs into the environment and prevent human health threats.
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