Isolation and Characterization of aSalmonella enterica Serotype Typhi Variant and Its Clinical and Public Health Implications

摘要

We report the isolation and characterization of a member of the family Enterobacteriaceae isolated from the gallbladder pus of a food handler. Conventional biochemical tests suggestedSalmonella enterica serotype Typhi, but the isolate agglutinated with poly(O), 2O, 9O, and Vi Salmonellaantisera but not with poly(H) or any individual HSalmonella antisera. 16S rRNA gene sequencing showed that there were two base differences between the isolate andSalmonella enterica serotype Montevideo, four base differences between the isolate and serotype Typhi, five base differences between the isolate and Salmonella entericaserotype Typhimurium, and six base differences between the isolate andSalmonella enterica serotype Dublin, indicating that the isolate was a strain of S. enterica. Electron microscopy confirmed that the isolate was aflagellated. The flagellin gene sequence of the isolate was 100% identical to that of the H1-d flagellin gene of serotype Typhi. Sequencing of the rfbEgene, which encoded the CDP-tyvelose epimerase of the isolate, showed that there was a point mutation at position +694 (G→T), leading to an amino acid substitution (Gly→Cys). This may have resulted in a protein of reduced catalytic activity and hence the presence of both 2O and 9O antigens. We therefore concluded that the isolate was a variant of serotype Typhi. Besides antibiotic therapy and cholecystectomy, removal of all stones in the biliary tree was performed for eradication of the carrier state.