Molecular analysis of strains of Shigella boydii isolated in northern and southern Italy.

In the years 1981-1988, Shigella boydii played a very limited role in the aetiology of diarrhoeal disease in Italy. However, between September and November, 1985, 19 isolates of serotype 2 were recovered in northern Italy from a dysentery outbreak which occurred in a geriatrics hospital in Abbiategrasso (Milan, Lombardy) and seven were identified in southern Italy during the period January-July, 1986 from apparently unrelated infection cases occurring in Brindisi (Apulia). These isolates were compared by molecular methods to seven strains of S. boydii of serotype 2 isolated since 1981 from the same geographic areas. Plasmid DNA analysis showed a large variety of patterns, whereas hybridization of chromosomal DNA with E. coli rRNA identified only two different profiles, one of which was exclusively found in all isolates from the hospital outbreak. No differences were detected among rDNA patterns of the remaining strains of S. boydii, irrespective of their geographic origin. These findings are consistent with the hypothesis that the infrequent cases of infection from S. boydii of serotype 2 which occurred during the years under study could probably be attributed to two different bacterial clones. Hybridization procedure and detection of hybrids were simplified by replacement of radioactive labelling of rRNA by the use of photobiotin.