P-023. Identification and Characterization of Class 1 Integron Resistance Genes Cassettes among Salmonella Strains from Imported Seafood

A. A. Khan1, E. Ponce2, C-M. Cheng3, M. Nawaz1, C. Summage-West1;
1U.S. FDA/Nat'l. Ctr. for Toxicol. Res., Jefferson, AR, 2Centro de Investigacionientifica y de Educaion Superior de Ensenada (CICESE), Ensenada, MEXICO, 3USFDA, Pacific Regional Lab.-SW, Irving, CA.

A total of 210 Salmonella isolates representing 20 serovars were isolated from imported seafood samples during the years 2001-2005. These isolates were tested for their susceptibility to thirteen antibiotics of veterinary and clinical importance. Fifty five strains were resistant to at least one antibiotic tested. Three Salmonella enterica serovars; Newport (62), Typhimurium varcopen (629), and Lansing (803) were originated from different countries (Hong Kong, Philippines and Taiwan) were highly resistant to multiple antibiotics including trimethoprim sulfamethoxazole, streptomycin and tetracycline. The pulsed-field gel electrophoresis (PFGE) of XbaI digested DNA showed all three strains are genetically distinct. These strains were further characterized for the presence of genomic island SGI1 and integrons. Two strains 629 and 803 amplified 500-bp product region of genomic island SGI1. Strain 62 was negative for genomic island SGI1 region. Primers specific to integron conserved sequence (CS) region amplified 1.24 Kb amplicon from strains 62 and 2 Kb amplicon from two isolates 629, and 803. Sequence analysis of 1.24 kb clone of 62 revealed the presence of dfrA1 conferring resistance to trimethoprim and orfC gene cassette of unknown function. The sequence analysis of 2 kb clone of 629 and 803 revealed the presence of dihydrofolate reductase type XII gene, dhfrXII gene cassette, which confers resistance to trimethoprim, 59 base element, orfF of hypothetical protein and an aminoglycoside adenylatetransferase gene, aadA2 gene cassette, which confers resistance to streptomycin and spectinomycin. Plasmid analysis of these strains revealed the presence of several plasmids in one strain 629. Southern hybridization of plasmid with integron probe showed that trimethoprim and streptomycin resistance genes are located on mega plasmid. This study indicates that antimicrobial-resistant Salmonella enterica serovars are present in imported seafoods and it is important to continue the surveillance of foodborne bacterial pathogens from imported foods.