Plasmid profile as a useful marker of a Shigella dysenteriae type 1 strain causing an epidemic of shigellosis.

Plasmid profiles of 60 Shigella dysenteriae type 1 isolates obtained during an epidemic period (April - October 1983) were compared with that of 74 other Shigella species isolated during the same period of time and also with that of 20 S. dysenteriae type 1 isolates obtained before the epidemic period (1969 - 1982). All samples were collected during an epidemic of shigellosis from diarrhoeal patients being treated at the Dhaka Treatment Centre of the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B) between April and October 1983. Approximately 4% of the patients were sampled. The isolated showed varied patterns of resistance to several antimicrobial agents. Ninety-two per cent of the 60 S. dysenteriae type 1 strains showed a typical profile of four plasmids with masses of 140, 6, 4 and 2 megadaltons (Mdal). The finding is in contrast with that of a previous study at the ICDDR,B, in which 14 different plasmid profiles were observed in 23 strains of S. dysenteriae type 1 isolated during a 10 - month period in 1982. The profile typical for this study was different from those found in other species of Shigella isolated at the same time. There was a strong association between the possession of this plasmid profile and resistance to chloramphenicol, streptomycin, tetracycline and trimethoprim - sulphamethoxazole. Twenty S. dysenterae type 1 strains isolated from the faeces of patients at the ICDDR,B during 1969 - 1982 were also analysed for their plasmid profiles. The finding is in contrast with that of the epidemic strains. The typical epidemic plasmid pattern, i.e. the 140, 6, 4 and 2 Mdal, was absent in isolates obtained before 1983 epidemic.(ABSTRACT TRUNCATED AT 250 WORDS)