Identification of Salmonella enterica Typhi which transferred multidrug-resistance by class1 integron associated novel gene casettes in Korea.

Abstract

MDR (multidrug-resistant) Salmonella Typhi has become an important pathogen in Southeast Asia. But there has been few MDR strain isolated in Korea. In 1999, 6 strains of Salmonella Typhi which were resistant to ampicillin, chloramphenicol, trimethoprim-sulfamethoxazole, streptomycin, tetracycline, and kanamycin were isolated nationwide. This multidrug resistance was transferred by about 49 kb sized conjugable plasmid. By PCR cloning method using the class 1 integron-specific primers, a part of the resistance determining region of the plasmid was cloned and sequenced. The plasmid harbored the novel class 1 integron associated gene cassettes, which contained six antimicrobial resistance genes; aacA4, catB8, aadA1, dhfR1, aac6-II, and novel blaCARB, blaCARB-8. Deduced amino acid sequences of the novel blaCARB showed one amino acid change from N29-like b-lactamase from Proteus mirabilis; Val->Ile at 90 amino acid. Six isolates with the same antimicrobial resistance patterns had the same sized plasmids and the same ribotyping patterns, which suggested the clonal spread of these MDR isolates. This is the first report of S. enterica Typhi in which the multidrug-resistance is mediated by class 1 integron associated gene cassettes.