IS200 Insertion between gyrA and rcsC Genes in Salmonella typhi

While probing DNA from 193 Salmonella isolates of 47 different serotypes, Calva et al. (3) found one of the copies of IS200 elements to be constantly present between the gyrA and rcsC genes in all 63 strains of Salmonella typhi examined. Apart from being localized in these S. typhi strains from different locations globally, IS200 was also localized at the identical place in 18 strains of S. weltevreden examined. This specific IS200 could be an important tool in molecular taxonomy and epidemiology for differentiation of S. typhi from nontyphoidal salmonellae if its specific localization could be demonstrated in S. typhi isolates from sites of multiplication other than the blood.

S. typhi has been implicated in two cases of sacroiliitis, in a 13-year-old female and a 37-year-old male in Qatar (1). Moreover, S. typhimurium has also been documented to cause sacroiliitis (2). Both S. typhi and S. paratyphi have emerged as opportunistic organisms in individuals infected with human immunodeficiency virus. Even in areas of nonendemicity, such coinfections present atypically with an aggressive clinical profile (4).

Undoubtedly, the specific IS200 localization of S. typhi (3) would show less promise if the technique fails to identify isolates from sites other than the bloodstream as well as from those from patients coinfected with AIDS. Any localization in nontyphoid salmonellae from atypical presentations would reduce the utility of IS200 significantly. Nevertheless, in-depth experimentation on salmonellae from a variety of sites of infection could serve to vindicate the reported sensitivity and specificity of IS200 localization between gyrA and rcsC (3) as a tool to differentiate typhoid and nontyphoid salmonellae.