Changing pattern of resistant Shiga bacillus (Shigella dysenteriae type 1) and Shigella flexneri in Bangladesh.

Shigella dysenteriae type 1 (Shiga bacillus) has made a dramatic comeback in Bangladesh after 10 years when Shigella flexneri was the dominant serogroup. Whereas S. flexneri showed little increase in resistance to the commonly used antimicrobial agents--namely, trimethoprim-sulfamethoxazole (TMP-SMX) and ampicillin-over the years, S. dysenteriae type 1 underwent rapid changes with regard to sensitivity pattern during the last two years. The first TMP-SMX-resistant strain of S. dysenteriae type 1 was detected in September 1982; however, by mid-1984 most strains were resistant while retaining sensitivity to ampicillin. During this period, the ratio of S. flexneri to S. dysenteriae type 1 narrowed from 0.15 to 1. Such propagation of high resistance to TMP-SMX might have been due to widespread use of the drug imported into the country in large quantities. Resistance to ampicillin is increasing rapidly, particularly in S. dysenteriae type 1.