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Updated: Jun 26, 2026

Isolation and Identification of Waterborne Antibiotic-Resistant Bacteria and Molecular Characterization of their Antibiotic Resistance Genes
Published on: March 3, 2023
Tetracycline-resistance genes in gram-negative isolates from estuarine waters
I S Henriques1, F Fonseca, A Alves
1CESAM & Department of Biology, University of Aveiro, 3810-193 Aveiro, Portugal. ihenriques@ua.pt
Aims:
To investigate the diversity and dissemination of tetracycline resistance genes in isolates from estuarine waters.
Methods And Results:
Forty-two out of 164 multi-resistant isolates previously obtained were resistant or less-susceptible to tetracycline, as evaluated by the disc diffusion method. Minimal inhibitory concentration for resistant bacteria ranged from 16 to 256 mg l(-1). Screening of tet genes by polymerase chain reaction showed that 88% of the isolates carried at least one of the genes tested, namely tet(A) (present in 13 isolates), tet(B) (present in 13 isolates), tet(C) (present in 3 isolates), tet(D) (present in 1 isolate), tet(E) (present in 6 isolates) and tet(M) (present in 1 isolate). One isolate carried tet(A) and tet(M). To our knowledge, this study presents the first description of a tet(D) gene in Morganella morganii. Hybridization revealed that tet genes were plasmid-located in 31% of the isolates. Those isolates were included as donors in conjugation experiments and 38% transferred tetracycline resistance.
Conclusions:
A considerable diversity of tet genes was detected in the estuary. Frequently, these genes were associated with plasmids and could be transferred to Escherichia coli.
Significance And Impact Of The Study:
The results presented provide further evidence of the role played by estuarine reservoirs in antibiotic resistance maintenance and dissemination.
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