Characteristics of Yersinia enterocolitica isolated from children with diarrhea in Italy.

Of 2,500 fecal samples collected from children with diarrhea in the province of Siena, 35 (1.4%) were found to be positive for Yersinia enterocolitica. Of the isolates, 94.2% belonged to biotype 4, serotype 0:3; 2.8% belonged to biotype 2, serotype O:9; and 2.8% belonged to biotype 1, serotype O:6. The in vitro pathogenicity tests showed that all but two isolates were calcium dependent and autoagglutinable and that all but one were also invasive in HEp-2 cell culture. As regards plasmid content, 32 of 33 biotype 4, serotype O:3 strains harbored a plasmid of 48 megadaltons and 1 strain also harbored a small plasmid of 2 megadaltons. The biotype 2, serotype O:9 strain harbored a plasmid of 42 megadaltons; one of the two strans lacking plasmids belonged to biotype 1, serotype O:6, and the other belonged to biotype 4, serotype O:3. Pyrazinamidase activity was positive only for the biotype 1, serotype O:6 strain. Esculin was hydrolyzed only by the biotype 1, serotype O:6 strain.