ABSTRACT
BACKGROUND: During the period from April to June 1996, an outbreak of typhoid fever occurred in SuYoung-Ku, Pusan city. We performed the molecular epidemiological analysis and drug susceptibility test for 48 isolates of Salmonella typhi from the outbreak. METHODS: Chromosomal DNA of S. typhi was digested with the restriction endonuclease Spe I and the resulting restriction polymorphism was observed on pulsed field gel electrophoresis (PFGE). Phage typing was performed using Vi-phages, and antimicrobial susceptibility test was done by Disc diffusion method. RESULTS: On phage typing, 2 isolates were M1 phage type, 2 E1 phage type and 44 untypable. The PFGE analysis on 14 to 16 chromosomal DNA restriction fragments ranged from 50 Kb to 1000kb showed 2 different patterns of restriction fragments, divided into group A and B. Forty-seven isolates belonged to group A that were allocated into A1 (42 strains), A2 (1 strain), A3 (3 strains), A4 (1 strain), and one strain was grouped into group B. In the F-value of genetic similarity of the epidemic S. typhi strains, there was low similarity (F value:0.2-0.258) between group A strains and group B strains. However, the subgroup strains (A1-A4) showed high similarity (F value:0.8-0.897) each other. The drug susceptibility test showed susceptibility to ampicillin, carbenicillin, cephalothin, chloramphenicol, tobramycin, gentamicin, kanamycin, nalidixic acid, neomycin, polymyxin B, streptomycin, tetracycline, trimethoprim-sulfamethoxazole, ciprofloxacin and norfloxacin. CONCLUSION: This study showed that phage typing and PFGE were very useful as a tool to investigate molecular analyses of epidemic S. typhi strains this study.