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      Molecular characterization of tetracycline- and quinolone-resistant Aeromonas salmonicida isolated in Korea

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          Abstract

          The antibiotic resistance of 16 Aeromonas ( A.) salmonicida strains isolated from diseased fish and environmental samples in Korea from 2006 to 2009 were investigated in this study. Tetracycline or quinolone resistance was observed in eight and 16 of the isolates, respectively, based on the measured minimal inhibitory concentrations. Among the tetracycline-resistant strains, seven of the isolates harbored tetA gene and one isolate harbored tetE gene. Additionally, quinolone-resistance determining regions (QRDRs) consisting of the gyrA and parC genes were amplified and sequenced. Among the quinolone-resistant A. salmonicida strains, 15 harbored point mutations in the gyrA codon 83 which were responsible for the corresponding amino acid substitutions of Ser 83→Arg 83 or Ser 83→Asn 83. We detected no point mutations in other QRDRs, such as gyrA codons 87 and 92, and parC codons 80 and 84. Genetic similarity was assessed via pulsed-field gel electrophoresis, and the results indicated high clonality among the Korean antibiotic-resistant strains of A. salmonicida.

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          Most cited references 38

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          Multiplex PCR for detection of plasmid-mediated quinolone resistance qnr genes in ESBL-producing enterobacterial isolates.

          To develop a rapid and reliable single-tube-based PCR technique for detecting simultaneously the plasmid-mediated quinolone resistance qnrA, qnrB and qnrS genes. After multiple alignments, primers were designed to detect known qnr variants (six for qnrA-, six for qnrB- and two for qnrS-like genes). They were used for screening a collection of 64 expanded-spectrum beta-lactamase (ESBL)-producing enterobacterial isolates from Kuwait, collected from 2002 to 2004, as ESBL genes have been often associated with qnr genes. Sequencing was performed to identify qnr and associated ESBL genes. In optimized conditions, all positive controls (used separately or mixed) confirmed the specificity of the PCR primers. Out of 64 isolates, only 3 isolates were positive for a qnrB-like gene (4.7%), whereas no qnrA-like and qnrS-like gene was detected. A qnrB2 gene was detected in an Enterobacter cloacae K34 (SHV-12+) isolate, whereas qnrB1-like (termed qnrB7) and qnrB6-like (termed qnrB8) genes were identified from E. cloacae K37 (SHV-12+) and Citrobacter freundii K70 (VEB-1b+) isolates, respectively. We report here a fast and reliable technique for rapid screening of qnr-positive strains to be used for epidemiological surveys. A low prevalence of Qnr determinants among ESBL-producing Enterobacteriaceae was identified in the study with Kuwaiti isolates.
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            Evolving concepts regarding the genus Aeromonas: an expanding Panorama of species, disease presentations, and unanswered questions.

            It has been almost 10 years since a major review on the association of Aeromonas with human disease has been published. During that period the number of valid species in the genus has grown to 14, with a new family (Aeromonadaceae) established to house this genus. Despite this explosion in the number of new genomospecies, only five (Aeromonas hydrophila, A. caviae, A. veronii, A. jandaei, and A. schubertii) are currently recognized as human pathogens. New syndromes attributed to this genus include hemolytic uremic syndrome, burn-associated sepsis, and a variety of respiratory tract infections, including epiglottitis. Convincing evidence suggests that some aeromonads do cause gastroenteritis, but it is presently unclear whether many of the strains isolated from feces are involved in diarrheal disease. Many questions regarding this genus remain unanswered.
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              The genome of Aeromonas salmonicida subsp. salmonicida A449: insights into the evolution of a fish pathogen

              Background Aeromonas salmonicida subsp. salmonicida is a Gram-negative bacterium that is the causative agent of furunculosis, a bacterial septicaemia of salmonid fish. While other species of Aeromonas are opportunistic pathogens or are found in commensal or symbiotic relationships with animal hosts, A. salmonicida subsp. salmonicida causes disease in healthy fish. The genome sequence of A. salmonicida was determined to provide a better understanding of the virulence factors used by this pathogen to infect fish. Results The nucleotide sequences of the A. salmonicida subsp. salmonicida A449 chromosome and two large plasmids are characterized. The chromosome is 4,702,402 bp and encodes 4388 genes, while the two large plasmids are 166,749 and 155,098 bp with 178 and 164 genes, respectively. Notable features are a large inversion in the chromosome and, in one of the large plasmids, the presence of a Tn21 composite transposon containing mercury resistance genes and an In2 integron encoding genes for resistance to streptomycin/spectinomycin, quaternary ammonia compounds, sulphonamides and chloramphenicol. A large number of genes encoding potential virulence factors were identified; however, many appear to be pseudogenes since they contain insertion sequences, frameshifts or in-frame stop codons. A total of 170 pseudogenes and 88 insertion sequences (of ten different types) are found in the A. salmonicida genome. Comparison with the A. hydrophila ATCC 7966T genome reveals multiple large inversions in the chromosome as well as an approximately 9% difference in gene content indicating instances of single gene or operon loss or gain. A limited number of the pseudogenes found in A. salmonicida A449 were investigated in other Aeromonas strains and species. While nearly all the pseudogenes tested are present in A. salmonicida subsp. salmonicida strains, only about 25% were found in other A. salmonicida subspecies and none were detected in other Aeromonas species. Conclusion Relative to the A. hydrophila ATCC 7966T genome, the A. salmonicida subsp. salmonicida genome has acquired multiple mobile genetic elements, undergone substantial rearrangement and developed a significant number of pseudogenes. These changes appear to be a consequence of adaptation to a specific host, salmonid fish, and provide insights into the mechanisms used by the bacterium for infection and avoidance of host defence systems.
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                Author and article information

                Journal
                J Vet Sci
                JVS
                Journal of Veterinary Science
                The Korean Society of Veterinary Science
                1229-845X
                1976-555X
                March 2011
                05 March 2011
                : 12
                : 1
                : 41-48
                Affiliations
                [1 ]Laboratory of Aquatic Animal Medicine, College of Veterinary Medicine and Research Institute for Veterinary Science, Seoul National University, Seoul 151-742, Korea.
                [2 ]Department of Microbiology, College of Veterinary Medicine and Research Institute for Veterinary Science, Seoul National University, Seoul 151-742, Korea.
                [3 ]Laboratory of Animal Cell Biotechnology, Department of Agricultural Biotechnology, Seoul National University, Seoul 151-742, Korea.
                Author notes
                Corresponding author: Tel: +82-2-880-1282; Fax: +82-2-880-1213, parksec@ 123456snu.ac.kr

                The first two authors contributed equally to this work.

                Article
                10.4142/jvs.2011.12.1.41
                3053466
                21368562
                Copyright © 2011 The Korean Society of Veterinary Science
                Categories
                Original Article

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