Molecular And Phenotypic Characterisation Of Non-Typhoidal Salmonella enterica Associated With Human Disease In The Gambia

Darboe, Saffiatou (2022). Molecular And Phenotypic Characterisation Of Non-Typhoidal Salmonella enterica Associated With Human Disease In The Gambia. MPhil thesis The Open University.



Background: Non-typhoidal Salmonella (NTS) are a major cause of foodborne gastroenteritis worldwide but have emerged as a significant cause of multi-drug resistant invasive disease in sub-Saharan Africa (sSA). Specific lineages of the Salmonella enterica subspecies enterica serovar Enteritidis (S. Enteritidis) and Salmonella enterica subspecies enterica serovar Typhimurium (S. Typhimurium) serovars are implicated, and genomic analysis has shown that these lineages in sSA are phylogenetically distinct from others causing gastroenteritis globally.

Methods: One hundred NTS isolates were collected from 93 patients presenting with clinical disease in 2001 from the eastern and 2006 to 2018 in the western regions of The Gambia. The isolates from the western region (n=80) were from blood (48), stool (25), cerebrospinal fluid (CSF; 1), abscesses (5), and urine (1) while those from the eastern region (n=20) also originated from blood (17), 2 CSF (2) and stool (1). The isolates were characterised by whole genome sequencing using Illumina platforms. Phenotypic susceptibility testing was done using Kirby Bauer disk diffusion. The sequence reads were analysed to determine lineages. Phylogenetic analysis was performed in the context of other African isolates from the European Nucleotide Archive.

Results: A total of 93 isolates (64 invasive, 23 gastroenteritis and 6 other infections) representing a single infection episode was analysed. S. Typhimurium (26/64; 30.6%) and S. Enteritidis (13/64; 20.3%) were the leading serovars associated with invasive disease respectively; whilst other serovars were mainly responsible for gastroenteritis (17/23; 73.9%). The presence of three major S. Enteritidis clades including the invasive West African clade (11/16; 68.8%) was confirmed. MDR was confirmed for seven isolates among the West African S. Enteritidis clade.

Conclusions: The study revealed insight into the dynamics of clinical NTS serovars in The Gambia. It has confirmed the presence of virulent multi-drug resistant S. Enteritidis highlighting the significance of surveillance in developing treatment guidelines.

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