Superinfection Compatibility of R Factors in Shigella dysenteriae Type 1 from Central America and Salmonella typhi from Mexico

Abstract

Tests of superinfection compatibility demonstrate that the R factors from the epidemic strains of Shigella dysenteriae type 1 and Salmonella typhi belong to different compatibility groups. The R factor from S. dysenteriae belongs to group O, with some partial incompatibility with the lex group, whereas the R factor from S. typhi is compatible with R factors from all groups tested. Thus the appearance of similar patterns of multiple antibiotic resistance in two unusual organisms that caused two major epidemics in the same geographic region within a short period was due to two unrelated R factors.