P-040. Isolation and Molecular Characterization of Tetracycline-Resistant Escherichia coli Isolated from Catfish

M. S. Nawaz, A. A. Khan, S. A. Khan, K. Sung, R. S. Steele;
US FDA/NCTR, Jefferson, AR.

A study was undertaken to determine the prevalence of tetracycline-resistant E. coli and the type of tetracycline resistance (tet) genes in farm raised catfish. Sixty-one tetracycline-resistant Escherichia coli strains were isolated from the intestinal contents of 407 farm raised catfish. All isolates were resistant to multiple antibiotics. A PCR assay detected tetA in the DNA of 15/61 (25.0%) of isolates by amplifying the PCR amplicon measuring 957-bp. Oligonucleotide primers specifically targeting a 436-bp region of tetB successfully amplified the PCR amplicon from 47/61 (77.0%) of the isolates, indicating that tetB may be the predominant tet genes in these isolates. Oligonucleotide primers specific for the amplification of tetC amplified the 589-bp PCR amplicon from 3/61 (5%) of the isolates. Eleven (11/61) of the isolates contained both tetA and tetB genes. Plasmids (2.0-16.0 kb) were found in only 37 of the 61 tetracycline-resistant E. coli strains. XbaI restriction digestion of the genomic DNA from 61 tetracycline-resistant E. coli strains yielded 15-30 DNA fragments measuring 2.03-194 kb in size. Pulsed field gel electrophoresis (PFGE) identified 18 distinct macrorestriction patterns (mrps) among the 61 isolates. The dendrogram analysis indicated that the DNA banding patterns of the 18 isolates were less than 60 % similar. Our results indicate that the use of tetracycline to control bacterial infections in catfish may have enhanced the prevalence of tetracycline resistant E. coli in farm raised catfish and that the catfish ecosystem could serve as a reservoir of tetracycline-resistance determinants.