Fluoroquinolone antibiotics (FQs) have been used worldwide for chemotherapy, animal husbandry, and aquaculture, and the occurrence of FQ-resistant (FQs
r) bacteria in natural environments has been reported. Plasmid-mediated transferable quinolone resistance (PMQR) genes are suspected to originate from the chromosomes of water-dwelling bacteria. However, the occurrence of and the potential reservoir of FQs
r bacteria and PMQR genes in aquatic environments have not been elucidated. In this study, we detected FQs
r bacteria and PMQR genes in aquatic environments in Thailand and Vietnam, and measured FQ contamination. Levels of contamination were greater Thailand (avg. 5130, max 46100 ng L
-1) than in Vietnam (avg. 235, max 1130 ng L
-1); however, the occurrence of FQs
r bacteria was higher in Vietnam (~15%) than in Thailand (~7.0%), suggesting that contamination by FQs is not directly linked to the development of FQs
r bacteria. Diverse taxonomic groups of FQs
r-bacteria were identified, and one of the PMQR genes,
qnrB, was detected from bacteria of environmental origin, not enteric bacteria. This suggests that the environmental bacteria are a potential reservoir of antibiotic resistance determinants even at un-contaminated sites.
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