Journal Article

Molecular Characterization of Salmonella Typhi Strains Isolated from Patients Clinically Diagnosed of Typhoid Fever in Kaduna State-Nigeria

Abstract

Typhoid fever; a systemic disease caused by Salmonella enterica serovar Typhi (S. Typhi) remains a major public health problem in many parts of the world. Accurate diagnosis of the disease requires isolation of the organism. Therefore, the main objective of this study was to molecularly characterized S. Typhi strains isolated from patients clinically diagnosed of typhoid fever in selected hospitals within Kaduna State-Nigeria. Stool and blood samples were collected and subjected to culture test. Salmonella positive cultures were subjected to PCR amplification of invA, tyv, fliC-d genes. Virulence antigen expressing S. Typhi was detected by PCR amplification of viaB gene. Salmonella Typhi strains were also determined by sequencing invA amplicons. Genetic relatedness of the strains were determined by phylogenetic analysis. Out of the 420 patients recruited, 22(5.2%) and 01(0.2%) had their stool and blood positive for Salmonella infection. Out of the 22 Salmonella stool culture positive, 15(68.2%) were true positive while 7(31.8%) were false positive. The only blood culture positive was confirmed to be real positive. The prevalence rate of Salmonella infection among the 420 patients was 3.8%. The prevalence rate of S. Typhi among the 420 patients was 1.2%. Eighty percent of the isolated S. Typhi expressed virulence antigen (Vi) while 20% lack Vi. Hundred percent of the isolated S. Typhi were S. Typhi str. CT18. The phylogenetic analysis indicated that the isolated S. Typhi CT18 strains were more related to each other than Typhi str.Ty2 which was more than them. Phylogenetic analysis also indicated that the isolated S. Typhi str. CT18 emerge from Typhi str.Ty2 due to clonal expansion over time. The use of molecular method in diagnosing typhoid fever is more accurate than culture methods. The circulating strain in the study areas was S. Typhi str. CT18 which are of high virulence.

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