Salmonella Typhi genotypic diversity, cluster identification and antimicrobial resistance determinants in Mukuru settlement, Nairobi Kenya.

BACKGROUND

Understanding the source of typhoid infections and the genetic relatedness of Salmonella Typhi (S. Typhi) by cluster identification in endemic settings is critical for establishing coordinated public health responses for typhoid fever management. This study investigated the genotypic diversity, antibiotic resistance mechanisms, and clustering of 35 S.Typhi strains isolated from cases and carriers in the Mukuru Informal Settlement.

METHODS

We studied 35 S.Typhi isolates, including 32 from cases and 3 from carriers, from study participants in the informal settlement of Mukuru, Nairobi, Kenya. Genomic DNA was extracted, and whole-genome sequencing (WGS) was performed to determine the phylogenetic relatedness of strains and detect antimicrobial resistance determinants (AMR). WGS data were analyzed using bioinformatics tools available at the Center for Genomic Epidemiology and Pathogenwatch platforms.

RESULTS

Genotype 4.3.1.2 EA3 was found to be dominant at 46% (16/35), followed by 4.3.1.2 EA2 at 28% (10/35), and 4.3.1.1 EA1 at 27% (9/35). A comparison of the isolates with global strains from Pathogenwatch identified close clustering with strains from Uganda, Tanzania, Rwanda, and India. Three isolates (9%) distributed in each cluster were isolated from carriers. All genotype 4.3.1.2 EA3 isolates were genotypically multidrug-resistant to ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole. Single mutations in the quinolone resistance-determining region were identified in the gyrA (S83Y) and gyrB (S464F) genes. All isolates associated with multidrug resistance showed the presence of the IncQ1 plasmid with the following genes: blaTEM-1B, catA1, sul1, sul2, and dfrA7.

CONCLUSION

The close phylogenetic relatedness between antimicrobial-resistant case isolates and carriage isolates indicates that typhoid carriage is a possible source of infection in the community. Comparative analysis with global isolates revealed that the Kenyan isolates share common lineages with strains from neighboring East African countries and India, suggesting regional dissemination of specific MDR clones. AMR was a major feature of the isolates. Surveillance and testing for antimicrobial susceptibility should inform options for the management of cases.