MOLECULAR ANALYSIS OF ENVIRONMENTAL AND HUMAN ISOLATES OF SALMONELLA-TYPHI

Molecular characterization of a total of 54 isolates of Salmonella typ hi from Santiago, Chile, was performed by pulsed-field gel electrophor esis (PFGE) after digestion of chromosomal DNA with three restriction endonucleases: XbaI (5'-TCTAGA-3'), AvrII (5'-CCTAGG-3'), and SpeI (5' -ACTAGT3'). Thirteen of the 54 isolates were obtained from environment al sources (sewage and river water), and the rest were isolates from c linical cases of typhoid fever. Considerable genetic diversity was det ected among the human isolates obtained in 1994, as evidenced by the p resence of 14 to 19 different PFGE patterns among 20 human isolates, w ith F (coefficient of similarity) values ranging from 0.69 to 1.0 (Xba I), 0.61 to 1.0 (AvrII), and 0.70 to 1.0 (SpeI). A total of eight phag e types were detected among these 20 isolates, with 50% possessing the E1 or 46 phage type. There was no correlation between PFGE pattern an d phage types. Similar diversity was seen among 21 isolates obtained i n 1983, with 17 to 19 PFGE patterns detected and F values of 0.56 to 1 .0 (XbaI), 0.55 to 1.0 (AvrII), and 0.67 to 1.0 (SpeI). Comparison of these two groups of human isolates obtained 11 years apart indicated t hat certain molecular types of S. typhi are shared and are able to per sist for considerable periods. A similar degree of genetic diversity w as also detected among the environmental isolates of S. typhi, for whi ch 10 to 12 different PFGE patterns were detected among the 13 isolate s analyzed, with F values ranging from 0.56 to 1.0 (XbaI), 0.52 to 1.0 (AvrII), and 0.69 to 1.0 (SpeI). Certain molecular types present amon g the environmental isolates of S. typhi were also found among the hum an isolates from the same time period, providing evidence for the epid emiological link between environmental reservoirs and human infection.