The genomic locus used as the diagnostic marker is potentially stable. Twenty clinical isolates from Pondicherry (southern India) and 12 clinical isolates from Nagpur (central India) were analyzed by colony PCR to show that the region is potentially stable. The amplified products were run on a 0.8% agarose gel. (A) The 20 clinical isolates (lanes 1 to 20) showed two bands, characteristic of S. Typhi CT18, which has also been confirmed through serotyping. (B) This representative gel shows 7 samples out of 12 samples obtained from patients in Nagpur, India. Among seven samples, three samples showed only the lower 384-bp band of S. Paratyphi A (lanes 2, 3, and 5), and four samples showed two bands of S. Typhi CT18 (lanes 1, 4, 6, and 7). Lanes 8, 9, and 10 contain controls with isolated colonies of S. Paratyphi A, S. Typhi CT18, and S. Typhi Ty2, respectively. M lanes contain molecular size markers.