Molecular Epidemiology of Shigella sonnei in Pima County, Arizona: Evidence for a Mexico-Related Plasmid

To investigate sources, Shigella isolates and epidemiologic data were collected for 79 cases of infection with Shigella sonnei, the most common species. Since S. sonneihas a single serotype, plasmid isolation wasattempted to refine the epidemiologic analysis. There were seven plasmid patterns containing 17,13,4,22,9,2, and 3 isolates. Twelve of 17 isolates associated with recent travel to Mexico were in a group distinguished by a 5.1-kilobase (kb) plasmid. This plasmid was used to probe Southern blots of plasmids from strains of all groups. The Mexico-related plasmid probe hybridized to all the 5.1-kbplasmids and to 5.5-and 7.4-kbplasmids from three other groups. Of the 79 isolates, 50 contained plasmids homologous to the Mexico-related plasmid probe, sug-gesting association with travel to Mexico. Shigellosis is a highly communicable infectious disease of the gastrointestinal tract characterized by bloody mucoid di-arrhea, fever, and abdominal pain. Transmission through water and food is responsible for most focal outbreaks. In the USA, 15,000-20,000 cases of shigellosis are reported annually. The most common Shigella species in developed countries i

Molecular epidemiology of Shigella infections: plasmid profiles, serotype correlation, and restriction endonuclease analysis

Plasmid isolation was used to refine the epidemiologic analysis for 168 shigellosis cases in Pima County, Ariz. Plasmids of less than 20 kb were used for comparison of plasmid profiles. Plasmid patterns for each species were distinct. A total of 57 of 74 (77%) Shigella flexneri strains could be placed into seven plasmid patterns, 70 of 79 (89%) Shigella sonnei strains could be placed into seven patterns, 12 Shigella boydii strains could be placed into six patterns, and each of 3 Shigella dysenteriae strains differed. There was a correlation between plasmid patterns and serotypes for S. flexneri, and multiple plasmid patterns were found in serotypes 1, 2, and 6, offering a refinement beyond serotyping. In previous studies we found an association between Mexican travel and an S. sonnei 5.1-kb plasmid. When this plasmid was used as a probe, strong homology was seen with numerous small plasmids in all Shigella species: restriction endonuclease analysis revealed a 1.1-kb AvaI-AvaII fragment common to various plasmids of S. sonnei. S. flexneri, and S. boydii independent of species. Of 34 Pima County Shigella isolates from the mid-1970s. 8 showed plasmid patterns similar to those of the recent isolates. Some plasmids from S. sonnei, S. flexneri, and S. boydii strains isolated in the 1970s also contained the AvaI-AvaII fragment. The conservation of this specific fragment in our population for more than 12 years suggests that it may contain genes important in virulence or survival.</jats:p