The prevalence of resistant genes against β-lactams in 119 Aeromonas strains was determined. A large number (99.2%) of the present fish strains were resistant to one or more β- lactams including ceftiofur, amoxicillin-clavulanic acid, ampicillin, piperacillin and cefpodoxime. Among antibiotic resistance phenotypes, the simultaneous resistance to all β-lactams occurred in 25.2% (n=30) of all strains, which consisted of 18 strains of A. dhakensis, 8 strains of A. caviae, 2 strains of A. hydrophila and only one strain of A. veronii. For exploring genetic background of the antibiotic resistances, multiple PCR assays were subjected to detect β-lactamase-encoding genes, bla(TEM), bla(OXA-B) and bla(CTX-M). In the results, the bla(TEM-1) gene was harbored in all strains, whereas only 3 strains harbored bla(OXA) gene. In the case of bla(CTX-M) gene, the gene was detected in 21.0% (25 out of 119) of all strains, which countered with 80% (20 out of 25) of A. dhakensis, 8% (2 out of 25) of A. caviae and 12% (3 out of 25) of A. hydrophila. In addition, most of the bla(CTX-M) positive strains showed simultaneous resistance to all β-lactams (18 out of 30 strains). In sequence analysis for bla(CTX-M) genes detected, they were CTX-M group 1-encoding genes including bla(CTX-M-33) from 3 eel strains of A. dhakensis. Therefore, A. dhakensis obtained from cultured fish could represent a reservoir for spreading genes encoding CTX-M group 1 enzymes and hence should be carefully monitored, especially for its potential risk to public health.

Journal of Animal Science and Technology (JAST) is a peer-reviewed, open access journal publishing original research, review articles and notes in all fields of animal science. Topics covered by the journal include: genetics and breeding, physiology, nutrition of monogastric animals, nutrition of ruminants, animal products (milk, meat, eggs and their by-products) and their processing, grasslands and roughages, livestock environment, animal biotechnology, animal behavior and welfare.

Aeromonas spp. have been recognized as important pathogens causing massive economic losses in the aquaculture industry. This study examined the resistance of fish Aeromonas isolates to 15 antibiotics and 3 heavy metals. Based on the results, it is suggested that selective antibiotheraphy should be applied according to the Aeromonas species and the cultured-fish species. In addition, cadmium-resistant strains were associated with resistance to amoxicillin/clavulanic acid, suggesting that cadmium is a global factor related to co-selection of antibiotic resistance in Aeromonas spp. Key words: Aeromonas spp., antibiotic resistance, heavy-metal resistance, aquaculture, multi-antibiotics resistance.

Thus far, Aeromonas aquariorum infection has been unrecorded in Korea. Herein, we report a fatal case of A. aquariorum infection in a 77-year-old male patient with liver cirrhosis. The bacterium isolated from a blood culture was initially mistaken as Aeromonas hydrophila using the Vitek2 identification system. In spite of intravenous ceftriaxone therapy, the patient was exacerbated by multiple organ dysfunction. By 4 days after admission, there was no hope for treatment or remission of symptoms and the patient was discharged. In the detailed microbiological investigations, the bacterium was identified as A. aquariorum harboring the act and alt genes, which encode cytotoxic and cytotonic enterotoxins.