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U.S. Department of Health and Human Services

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January-March 2006


MARCH: NCTR RESEARCH HIGHLIGHTS


Characterization of Tetracycline-Resistant Aeromonas spp. from Catfish
Aeromonas spp. are opportunistic pathogens that cause infectious diseases in fish and humans.

Broad spectrum antibiotics such as oxytetracycline and Romet are approved in aquaculture for the control of infections caused by the bacteria. However, widespread use of the antibiotic may result in the selection of tetracycline-resistant bacteria in an aquaculture environment and may play a role in the dissemination of antibiotic-resistant genes to clinical aeromonad strains.

NCTR scientists isolated 81 tetracycline-resistant Aeromonas spp. from 190 catfish samples obtained from commercial ponds in 3 states. Conventional biochemical techniques grouped the 81 isolates into 5 different species. However, the molecular method (PCR-RFLP of the 16S rRNA) indicated that all 81 tetracycline-resistant aeromonads were strains of Aeromonas veronii. All isolates were resistant to multiple antibiotics. A multiplex PCR was designed to amplify the tetracycline-resistant determinants (tetA-E) from the genomic DNA of all 81 isolates. The assay indicated that tetE was the most dominant tet gene in aeromonads. These isolates were further characterized by pulsed field gel electrophoresis (PFGE). Based on the SpeI-PFGE profiles and dendogram analysis, 15 distinct patterns were observed among the 81 isolates. The results indicate the need for use of molecular techniques for typing the isolates and the prevalence of catfish as a reservoir of tet genes.

For more information, contact Dr. M. Nawaz, Division of Microbiology, NCTR.