, Volume 72, Issue 4, pp 811-820

Bacterial degradation of antibiotic residues in marine fish farm sediments of Uranouchi Bay and phylogenetic analysis of antibiotic-degrading bacteria using 16S rDNA sequences

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Abstract

Antibiotic residues in marine sediments of fish farms negatively influence microbial ecologic systems. The microbial degradation of antibiotic residues was experimentally examined in the marine sediments of Uranouchi Bay, to which one of five antibiotics was added. After incubation reducing physical factors, ampicillin, doxycycline, oxytetracycline, and thiamphenicol were significantly degraded, while josamycin maintained most of the initial amounts. The isolates resistant to ampicillin, josamycin, oxytetracycline, or thiamphenicol degraded each antibiotic in wide ranges of degrees, whereas the isolates degrading doxycycline were not obtained. Microbial degradation may contribute to the disappearance of ampicillin, doxycycline, oxytetracycline, and thiamphenicol in the fish farm. In contrast, the disappearance of josamycin would depend on physical factors, but the bacteria degrading josamycin at least exist in the marine sediments. Phylogenetic analysis using 16S rDNA sequences demonstrated that the antibiotic-resistant isolates formed several clusters in the Gram-positive bacterial group, the Flavobacterium-Cytophaga-Bacteroides group, and the proteobacteria subdivisions. The antibiotic-resistant bacterial population would be composed of various species including ubiquitous coastal bacterial groups. Several species of antibiotic resistant bacteria show antibiotic degradation activities, and appear to contribute to the disappearance of antibiotics in Uranouchi Bay.