Use of pulsed field gel electrophoresis as an epidemiological tool for analysis of sporadic associated strains of Salmonella typhi isolated in Taiwan

In order to characterize the subtypes of Salmonella typhi which cause spora dic disease in Taiwan, 55 isolates of Salm. typhi obtained from unrelated p atients of sporadic cases during 1992-96 were subjected to chromosomal DNA digestion and pulsed field gel electrophoresis (PFGE). When DNAs of these 5 5 Salm. typhi strains were digested with XbaI, 41 PFGE patterns were observ ed. Strains sharing the same XbaI digestion pattern could not be further di scriminated by PFGE analysis using SpeI and NotI as digestion enzymes. Thus , considerable genetic diversity exists among the Salm. typhi isolates. Alt hough strains of the same patterns were mainly isolated during the same tim e, recirculation of certain infectious strains could be possible. When 12 a ntibiotics, i.e. ampicillin, trimethoprim/ sulfamethoxazole, erythromycin, norfloxacin, tetracycline, sulphonamide, streptomycin, neomycin, chloramphe nicol, kanamycin, cefoperazone and gentamycin were used to test the antibio tic susceptibility for these Salmonella isolates, only three antibiogram pa tterns were obtained and 49 of the 55 Salm. typhi isolates were found to be long to one pattern. Phage typing and plasmid profiles were also poor in di scriminating these strains. Thus, PFGE alone may be used as a powerful tool for analysis of sporadic associated Salm. typhi strains.