Decoding the invasive nature of a tropical pathogen of concern: The invasive non-Typhoidal Salmonella strains causing host-restricted extraintestinal infections worldwide

Global burden, subtype, risk factors and etiological analysis of enteric infections from 1990-2021: population based study

Background

Enteric infections represent a prevalent global health issue and contribute significantly to the global disease burden. This study aims to investigate the patterns and trends of enteric infections from 1990 to 2021, providing valuable insights for health policy formulation, medical resource allocation, and the optimization of patient management plans.

Methods

We analyzed the Global Burden of Disease (GBD) 2021 for 21 regions and 204 countries to understand better the health burden using prevalence, incidence, mortality, and disability-adjusted life years (DALYs), subtype, risk factors, and etiology. We tested correlations with the Socio-demographic Index (SDI), and using decomposition analysis to dissect the reasons behind changes in epidemiological indicators of the disease.

Results

In 2021, the age-standardized rates of prevalence, incidence, deaths, and DALYs per 100,000 population for enteric infections were 879.58, 577.21, 17.83, and 1020.15, respectively. Compared to 1990, these rates exhibited -0.18, -0.12, -0.73, and -0.72 changes. Gender and age analyses revealed a higher burden among females, those under 15 years old, and the elderly. Regions with low SDI had higher epidemiological indicators. The burden of Typhoid fever declines in high-development regions. Unsafe water sources were identified as the primary risk factor globally in both 1990 and 2021. Rotavirus was the leading cause of deaths and DALYs.

Conclusion

This study highlights the complex epidemiological landscape of enteric infections, revealing variations in burden, risk factors, and etiological characteristics across age, gender, and geographical regions. It underscores the urgent need for healthcare professionals and policymakers to develop innovative prevention and healthcare strategies based on the current and evolving burden of enteric infections, to alleviate the global disease burden.

Foodborne Infections and Salmonella: Current Primary Prevention Tools and Future Perspectives

Salmonella is considered the major zoonotic and foodborne pathogen responsible for human infections. It includes the serovars causing typhoid fever (S. typhi and S. paratyphi) and the non-typhoidal salmonella (NTS) serovars (S. enteritidis and S. typhimurium), causing enteric infections known as "Salmonellosis". NTS represents a major public health burden worldwide. The consumption of S. enteritidis-contaminated animal foods is the main source of this disease in humans, and eradicating bacteria from animals remains a challenge. NTS causes various clinical manifestations, depending on the quantity of bacteria present in the food and the immune status of the infected individual, ranging from localized, self-limiting gastroenteritis to more serious systemic infections. Salmonellosis prevention is based on hygienic and behavioral rules related to food handling that aim to reduce the risk of infection. However, no vaccine against NTS is available for human use. This aspect, in addition to the increase in multidrug-resistant strains and the high morbidity, mortality, and socioeconomic costs of NTS-related diseases, makes the development of new prevention and control strategies urgently needed. The success of the vaccines used to protect against S. typhi encouraged the development of NTS vaccine candidates, including live attenuated, subunit-based, and recombinant-protein-based vaccines. In this review, we discuss the epidemiological burden of Salmonellosis and its primary prevention, focusing on the current status and future perspectives of the vaccines against NTS.

A genome-wide collection of barcoded single-gene deletion mutants in Salmonella enterica serovar Typhimurium

Genetic screening of pools of mutants can reveal genetic determinants involved in complex biological interactions, processes, and systems. We previously constructed two single-gene deletion resources for Salmonella enterica serovar Typhimurium 14028s in which kanamycin (KanR) and chloramphenicol (CamR) cassettes were used to replace non-essential genes. We have now used lambda-red recombination to convert the antibiotic cassettes in these resources into a tetracycline-resistant (TetR) version where each mutant contains a different 21-base barcode flanked by Illumina Read1 and Read2 primer sequences. A motility assay of a pool of the entire library, followed by a single-tube processing of the bacterial pellet, PCR, and sequencing, was used to verify the performance of the barcoded TetR collection. The new resource is useful for experiments with defined subsets of barcoded mutant strains where biological bottlenecks preclude high numbers of founder bacteria, such as in animal infections. The TetR version of the library will also facilitate the construction of triple mutants by transduction. The resource of 6197 mutants covering 3490 genes is deposited at Biological and Emerging Infections Resources (beiresources.org).

Pan msr gene deleted strain of Salmonella Typhimurium suffers oxidative stress, depicts macromolecular damage and attenuated virulence

Salmonella encounters but survives host inflammatory response. To defend host-generated oxidants, Salmonella encodes primary antioxidants and protein repair enzymes. Methionine (Met) residues are highly prone to oxidation and convert into methionine sulfoxide (Met-SO) which compromises protein functions and subsequently cellular survival. However, by reducing Met-SO to Met, methionine sulfoxide reductases (Msrs) enhance cellular survival under stress conditions. Salmonella encodes five Msrs which are specific for particular Met-SO (free/protein bound), and 'R'/'S' types. Earlier studies assessed the effect of deletions of one or two msrs on the stress physiology of S. Typhimurium. We generated a pan msr gene deletion (Δ5msr) strain in S. Typhimurium. The Δ5msr mutant strain shows an initial lag in in vitro growth. However, the Δ5msr mutant strain depicts very high sensitivity (p < 0.0001) to hypochlorous acid (HOCl), chloramine T (ChT) and superoxide-generating oxidant paraquat. Further, the Δ5msr mutant strain shows high levels of malondialdehyde (MDA), protein carbonyls, and protein aggregation. On the other side, the Δ5msr mutant strain exhibits lower levels of free amines. Further, the Δ5msr mutant strain is highly susceptible to neutrophils and shows defective fitness in the spleen and liver of mice. The results of the current study suggest that the deletions of all msrs render S. Typhimurium highly prone to oxidative stress and attenuate its virulence.