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Invasive atypical non-typhoidal Salmonella serovars in The Gambia.

ABSTRACT: Invasive non-typhoidal Salmonella (iNTS) disease continues to be a significant public health problem in sub-Saharan Africa. Common clinical misdiagnosis, antimicrobial resistance, high case fatality and lack of a vaccine make iNTS a priority for global health research. Using whole genome sequence analysis of 164 invasive Salmonella isolates obtained through population-based surveillance between 2008 and 2016, we conducted genomic analysis of the serovars causing invasive Salmonella diseases in rural Gambia. The incidence of iNTS varied over time. The proportion of atypical serovars causing disease increased over time from 40 to 65 % compared to the typical serovars Enteritidis and Typhimurium that decreased from 30 to 12 %. Overall iNTS case fatality was 10%, but case fatality associated with atypical iNTS alone was 10 %. Genetic virulence factors were identified in 14/70 (20 %) typical serovars and 45/68 (66 %) of the atypical serovars and were associated with: invasion, proliferation and/or translocation (Clade A); and host colonization and immune modulation (Clade G). Among Enteritidis isolates, 33/40 were resistant to four or more of the antimicrobials tested, except ciprofloxacin, to which all isolates were susceptible. Resistance was low in Typhimurium isolates, but all 16 isolates were resistant to gentamicin. The increase in incidence and proportion of iNTS disease caused by atypical serovars is concerning. The increased proportion of atypical serovars and the high associated case fatality may be related to acquisition of specific genetic virulence factors. These factors may provide a selective advantage to the atypical serovars. Investigations should be conducted elsewhere in Africa to identify potential changes in the distribution of iNTS serovars and the extent of these virulence elements.

SUBMITTER: Kanteh A

PROVIDER: S-EPMC8743563 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:IntroductionSalmonella is considered one of the most significant pathogens in public health since it is a bacterium that is frequently linked to food-borne illnesses in humans. Some Salmonella serovars are responsible for outbreaks that are connected to the consumption of animal products. Cattle are connected to humans through a shared environment and the food chain as a significant source of animal protein. In Nigeria, antimicrobial medications are easily accessible for use in food-producing animals. Abattoir environments are reservoirs of foodborne bacteria like non-typhoidal Salmonella enterica (NTS), that have become resistant to antibiotics used for prophylaxis or treatment in animals. This study investigated the prevalence and resistance patterns of Salmonella enterica serovars in abattoir employees, beef cattle and abattoir environments in Abuja and Lagos, Nigeria.MethodsA total of 448 samples were collected from healthy personnel, slaughtered cattle, and abattoir environments between May and December 2020. Using Kirby-Bauer disk diffusion method, the resistance profile of NTS isolates were determined. Multidrug resistance (MDR) was considered when NTS was resistant to ≥3 antimicrobial drug classes. We performed phenotypic and genotypic characterizations of all Salmonella isolates including serotyping. Descriptive statistics were used to analyze the data.ResultsTwenty-seven (6%) NTS isolates were obtained. Prevalence of NTS was highest in abattoir environments (15.5%; 9/58), followed by cattle (4.8%;13/272) and abattoir employees (4.2%; 5/118). A high prevalence of resistance was observed for gentamicin (85.2%; 23/27) and tetracycline (77.8%; 21/27). Whole-genome sequencing of 22 NTS showed dissemination of aac(6')-laa (22/22), qnrB19 (1/22), fosA7 (1/22), and tetA (1/22) genes. Serovar diversity of NTS varied with source. S. Anatum, a rare serovar predominated with a prevalence of 18.2% (4/22). Chromosomal point mutations showed ParC T57S substitution in 22 NTS analyzed. Among 22 NTS, 131 mobile genetic elements (MGEs) were detected including insertion sequences (56.5%) and miniature inverted repeats (43.5%). Two integrating MGEs IS6 and IS21 were observed to carry the tetA gene + Incl-1 on the same contig in NTS originating from cattle. Rare serovars namely S. Abony and S. Stormont with MDR phenotypes recovered from cattle and abattoir environments were closely related with a pairwise distance of ≤5 SNPs.ConclusionsFirst report of rare serovars in Nigeria with MDR phenotypes in humans, cattle, and abattoir environments. This study demonstrates the spread of resistance in the abattoir environment possibly by MGEs and emphasizes the importance of genomic surveillance. Beef cattle may be a risk to public health because they spread a variety of rare Salmonella serovars. Therefore, encouraging hand hygiene among abattoir employees while processing beef cattle will further reduce NTS colonization in this population. This requires a One Health collaborative effort among various stakeholders in human health, animal health, and environmental health.

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Invasive atypical non-typhoidal Salmonella serovars in The Gambia.

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