Multiple-locus variable-number tandem-repeat analysis of Salmonella enterica serovar Typhi

Area of Science:

• Microbiology
• Genetics
• Epidemiology

Background:

• Multilocus variable-number tandem repeats (VNTRs) are crucial molecular markers for distinguishing homogeneous pathogenic bacterial clones.
• Salmonella enterica serovar Typhi presents a significant public health challenge, necessitating robust typing methods for epidemiological surveillance.

Purpose of the Study:

• To identify and evaluate novel VNTR markers for Salmonella Typhi.
• To assess the discriminatory power of Multilocus VNTR Analysis (MLVA) for typing Salmonella Typhi isolates.
• To compare MLVA-based phylogenetic inferences with those derived from single nucleotide polymorphism (SNP) typing.

Main Methods:

• Genome exploration of Salmonella Typhi strains CT18 and Ty2 to identify potential VNTR loci.
• Screening of 43 potential VNTRs, identifying two polymorphic markers.
• Typing of 73 global Salmonella Typhi isolates using a combined set of nine polymorphic VNTRs.
• Phylogenetic analysis of MLVA profiles and comparison with previous SNP typing data.

Main Results:

• Two novel polymorphic VNTRs were identified, adding to seven previously established markers.
• Multilocus VNTR Analysis (MLVA) generated 70 distinct profiles from 73 isolates, achieving a discriminatory power of 0.999.
• MLVA clustered isolates into seven groups, but phylogenetic relationships conflicted with SNP typing for distantly related isolates.

Conclusions:

• MLVA is effective for resolving relationships among closely related Salmonella Typhi isolates.
• A combined approach of SNP typing and MLVA typing offers superior resolution for both local and global epidemiological and evolutionary analyses of Salmonella Typhi.
• A standardized typing scheme using seven highly polymorphic VNTRs is recommended for epidemiological surveillance of Salmonella Typhi.