Background: Shigella sonnei isolates are homogeneous when examined by serological methods. Since this micro-organism is one of the common isolates in outbreaks of shigellosis, a strong necessity was felt to find a sub-division of it, useful in epidemiological studies.
Methods: 103 phages previously found to be active on various groups of Enterobacteriaceae were tested on 129 strains of S. sonnei. Among 47 phages active on S. sonnei, eight were selected as giving the best differentiation between the isolates and clear-cut reactions.
Results: Twelve main phage-types were identified. Among the strains of phage-type 1, some showed full sensitivity to all the eight phages; others showed minor differences in the sensitivity to one or some of them. The significance of these minor phage-types has to be further analyzed.
Conclusions: A tentative phage-typing scheme appropriate for S. sonnei has been proposed. This method provides a potentially useful tool for epidemiological study of this organism. Further validation of the scheme using local isolates is necessary.