Distribution and characterization of class 1 integrons in Salmonella enterica serotype Gallinarum biotype Gallinarum.

Fowl typhoid caused by Salmonella enterica subsp. enterica serotype Gallinarum biotype Gallinarum is the most important chicken disease in Korea. Due to appearance of new or multiple antibiotics resistances in the recently isolated strains, it was difficult to control the disease using antibiotics in our country. Therefore, the prevalence and genetic contents of class 1 integrons in biotype Gallinarum isolated between 1992 and 2001 were investigated by PCR and direct sequencing, respectively. Out of 90 strains, 35 (39%) carried class 1 integrons. The 1.0, 1.6 and 2.0kbp amplicons were amplified in 32 strains (36%), 2 strains (2%) and 1 strain (1%), respectively. The 1.0, 1.6 and 2.0 kbp amplicons contained one (aadA1a), two (aadB-aadA1b) and three cassettes (dhfrXII-orfF-aadA2), respectively, providing resistances against aminoglycosides (aadA1a, aadA1b, aadB, and aadA2) and trimethoprim (dhfrXII). The integron-carrying strains of biotype Gallinarum appeared in 1996 and acquired additional cassettes in 2000. Although the resistances to ampicillin, tetracycline and chloramphenicol are unrelated to class 1 integrons, relatively high prevalence of integron in biotype Gallinarum may be a dormant threat to the chemotherapy of the disease in the near future because of potency to acquire additional antibiotics resistances.

Antimicrobial resistance in Salmonella enterica serovars Enteritidis and Typhimurium isolated from animals in Korea: comparison of phenotypic and genotypic resistance characterization.

Fourteen and 22 each of Salmonella Enteritidis and Salmonella Typhimurium (S. Typhimurium) were isolated from animals from 1983 to 1999 in Korea and tested for their antibiotic resistance patterns, phage types and resistance gene patterns. S. Typhimurium isolates were highly resistant to streptomycin, sulfisoxazole and tetracycline, 95, 95 and 86%, respectively. The incidence of multiple antibiotic resistance (resistant to more than two drugs tested) of S. Typhimurium isolates was extremely high (100%) comparing to S. Enteritidis isolates (21%). Two of the five ACSSuT (ampicillin, chloramphenicol, streptomycin, sulfisoxazole and tetracycline) resistant type S. Typhimurium isolates were phage type definitive type 104 (DT104). For the detection of resistance related genes in S. Enteritidis and S. Typhimurium isolates, particularly ACSSuT type S. Typhimurium, antibiotic resistance genes, cmlA/tetR, bla(PSE-1) and bla(TEM), and genus Salmonella specific gene, sipB/C, were amplified using four pairs of primers in a hot-start multiplex polymerase chain reaction (PCR). Two Korean isolates of S. Typhimurium DT104 showed bla(TEM) amplicons instead of bla(PSE-1) for the ampicillin resistance and they were susceptible to florfenicol. The multiplex PCR used in this study was useful in characterization of multiple drug resistant Salmonella isolates, especially ACSSuT type S. Typhimurium, and identification of beta-lactamase gene distribution among Salmonella isolates.