Abstract
The objective of this study was to monitor changes (amplification or attenuation) in antibiotic resistance during wastewater treatment based on the ecology of tetracycline-resistant bacteria. The untreated and treated wastewater were collected in four seasons. Number of tetracycline-(TETR ) and oxytetracycline-resistant (OTCR ) bacteria, their qualitative composition, minimum inhibitory concentrations (MICs), sensitivity to other antibiotics, and the presence of tet (A, B, C, D, E) resistance genes were determined. TETR and OTCR counts in untreated wastewater were 100 to 1000 higher than in treated effluent. OTCR bacterial counts were higher than TETR populations in both untreated and treated wastewater. TETR isolates were not dominated by a single bacterial genus or species, whereas Aeromonas hydrophila and Aeromonas sobria were the most common in OTCR isolates. The treatment process attenuated the drug resistance of TETR bacteria and amplified the resistance of OTCR bacteria. In both microbial groups, the frequency of tet (A) gene increased in effluent in comparison with untreated wastewater. Our results also indicate that treated wastewater is a reservoir of multiple drug-resistant bacteria as well as resistance determinants which may pose a health hazard for humans and animals when released to the natural environment.
Highlights
Microbial resistance to drugs poses a growing threat for human health and life
Vast similarities are observed in TETR bacteria's share of Heterotrophic plate counts (HPC) which was determined at 0 to 2% by Kim et al [20], Huang et al [11] and Munir et al [21] and at 1.61% in this study
TetR isolates were not marked by a predominance of a single bacterial species or genus, whereas bacteria of the genus Aeromonas were the most abundant microorganisms in the group of OTCR isolates
Summary
The widespread use of antibiotics in the treatment of bacterial diseases has contributed to the development of strains that are resistant to this group of drugs. The problem is deepened by the existence of large bacterial populations, short generation times and effective mechanisms of genetic information exchange [4]. Municipal treatment plants are supplied with wastewater generated by households, hospitals, public utility buildings, industrial plants as well as rain water. This combination of organic substances, biogenic elements and trace amounts of antibiotics supports the development and survival of drug-resistant bacteria [8]. The above facilitates the exchange of genes located on mobile plasmids, including those encoding drug resistance [10]
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