A case of shigellosis caused by Shigella dysenteriae type 1 and Shigella flexneri type 5B.

Shigella dysenteriae type 1 and Shigella flexneri type 5b strains were isolated as causative agents of bacterial dysentery in a patient having visited South-East Asia. Both strains are a rare finding for Bulgaria. S. dysenteriae 1 strains have not been isolated since 1962, and there were only single isolates of S. flexneri 5b. The strains were of the same antibiotic resistance patterns. Conjugation experiments showed that resistance is determined by transferrable R-plasmids having identical characteristics. It is assumed that in the patient's gut transfer of an R-plasmid occurs from E. coli of the normal flora to the pathogenic shigellae.