SHIGELLA-SONNEI STRAINS ISOLATED FROM US SUMMER STUDENTS IN GUADALAJARA, MEXICO, FROM 1986 TO 1992

Plasmid DNA analysis and antibiotic susceptibilities were used to stud y strains of Shigella sonnei isolated from U.S. travelers to Guadalaja ra, Mexico, over a period of seven years (1986 to 1992). One hundred s ixty-one isolates were analyzed. By the use of duster analysis, eight different plasmid profiles were identified during this interval. At an y point in time, three to seven different plasmid profiles were presen t in this population. The introduction of strains that carried a new p lasmid with a molecular mass of 5.1 MDa was coincidental with an incre ase in isolation of S. sonnei in 1988. This new plasmid was present in 87.5% of the isolates that were resistant to chloramphenicol, Shigell osis in Guadalajara follows a pattern of hyperendemic transmission wit h transient peaks of high-frequency isolation of S. sonnei. This patte rn results from the concurrent presence of a heterogeneous group of st rains as opposed to the widespread transmission of one or a few clones .