Plasmid characterization of drug-resistant Shigella dysenteriae 1 from an epidemic in Central Africa.

A widespread epidemic of severe dysentery in Zaire and neighbouring Central African countries was caused by a multiply drug-resistant strain of Shigella dysenteriae 1. Early isolations were resistant to ampicillin, chloramphenicol, streptomycin, sulphonamides and tetracyclines (R-type = ACSSuT). Later in the epidemic strains resistant to trimethoprim (Tm) became prevalent and a few strains resistant to kanamycin (K) or nalidixic acid were also isolated. All resistances except nalidixic acid were encoded by plasmids of incompatibility groups X (ACT) or I1 (ACSSuTTm) and the epidemic strain also carried an SSu plasmid and a number of cryptic plasmids. The Inc X plasmid from this epidemic is the same as that in Sh. dysenteriae 1 strains isolated in Somalia in 1976 whereas the epidemic strains from the Shiga outbreaks in Central America, 1969 to 1971, and Sri Lanka, 1979, carried plasmids of group B. This epidemic demonstrates that when a multiresistant strain includes resistance to trimethoprim, nalidixic acid is a suitable alternative therapeutic agent.