Molecular analysis of S. paratyphi A from an outbreak in New Delhi, India

Abstract

Outbreaks of enterik fever caused by S. paratyphi A has never been reported until an outbreak occurred in New Delhi, India during September and October, 1996. We performed molecular analysis of 13 outbreak and 5 sporadic isolates of S. paratyphi A from this outbreak using pulsed-field gel electrophoresis (PFGE) and ribotyping. Genomic DNA were digested with XbaI antl Spel prior to PFGE analysis and ribotyping was performed using an rRNA gene probe derived from plasmid pKK35j5. By PFGE using both restriction endonucleases, the 5 sporadic isolates had 5 dffirent/unique DNA band patterns (F, coefficien of similarity, 0,63-0.76) whereas 4 closelyrelated PFGE patterns (F 0.8-1.0) were noted among the l3 outbreak isolates. None of the patterns present among the sporadic isolates were seen among the outbreak strains. The patterns observed were also dfferent compared to Malaysian S. paratyphi A strainsts. Similar results were seen with ribotyping although fewer DNA bands were seen as compared to PFGE. These results confirm the findings previously observed with S. typhi in that outbreak isolates are more clonal and homogeneous compared to sporadic isolates. The data also reaffirms the usefullness of molecular typing methods in the discrimination of salmonellae for epidemiological purposes.