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Tetracycline-resistant (Tet r ) bacteria were isolated from fishes collected at three different fish farms in the southern part of Japan in August and September 2000. Of the 66 Tet r gram-negative strains, 29 were identified as carrying tetB only. Four carried tetY, and another four carried tetD. Three strains carried tetC, two strains carried tetB and tetY, and one strain carried tetC and tetG. Sequence analyses indicated the identity in Tet r genes between the fish farm bacteria and clinical bacteria: 99.3 to 99.9% for tetB, 98.2 to 100% for tetC, 99.7 to 100% for tetD, 92.0 to 96.2% for tetG, and 97.1 to 100% for tetY. Eleven of the Tet r strains transferred Tet r genes by conjugation to Escherichia coli HB-101. All transconjugants were resistant to tetracycline, oxycycline, doxycycline, and minocycline. The donors included strains of Photobacterium, Vibrio, Pseudomonas, Alteromonas, Citrobacter, and Salmonella spp., and they transferred tetB, tetY, or tetD to the recipients. Because NaCl enhanced their growth, these Tet r strains, except for the Pseudomonas, Citrobacter, and Salmonella strains, were recognized as marine bacteria. Our results suggest that tet genes from fish farm bacteria have the same origins as those from clinical strains.Many different kinds of antibiotics have been used as therapeutic agents in aquaculture in Japan. Intensive work was done until the 1980s to develop guidelines for antibiotic usage in fish farms. The guidelines regulated doses and required a period of drug-free rearing before sale of fish and succeeded in keeping the residual antibiotics in cultured fish to nondetectable levels. However, Samuelsen et al. (35) found that antibiotic-resistant bacteria persisted in fish farm sediments for at least 18 months after chemotherapy. Since the products of aquaculture are consumed by humans and since many antibiotic resistance determinants are encoded by transferable plasmids, cultured fish may serve as a vehicle for transmission of antibiotic resistance to bacteria that are commensal or pathogenic to humans (34).Tetracyclines are among the therapeutic agents most commonly used in human and veterinary treatment. Oxytetracycline is permitted to be mixed with feed for fish, and food sanitation law in Japan permits certain residual levels in fish. Because of the widespread use of tetracycline, resistance to it has been disseminated to many species of marine bacteria (4,6,18,42,46).More than 30 different kinds of tetracycline resistance determinants have been published. Resistance genes have been mainly categorized into two major groups, those responsible for proton-dependent efflux of tetracycline (24) and those conferring ribosomal protection by cytoplasmic proteins (9). Dissemination of the proton-dependent tetracycline efflux protein in aquaculture environments has been reported (5,12,13,14,22,34,37). Previous work has identified the relevant genes by using DNA hybridization or PCR methods (4,12,13,14,15,16,27,28,34,37), but the nucleotide sequences of these determinants remain unkn...

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Sixteen strains of aerobic bacteria which contain bacteriochlorophyll a were isolated from the samples collected in aerobic marine environments: thalli of Enteromorpha linza, Porphyra sp., Sargussum horneri; beach sand; and the surface seawater from Aburatsubo Inlet. When they occurred, their proportions among the aerobic heterotrophic populations ranged from 0.9 to 1.1% in the seaweed samples and from 1.2 to 6.3% in the beach sand samples and were 0.9% in the seawater sample. The results suggested that the aerobic photopigmented bacteria widely inhabit aerobic marine environments.