Infection biology of Salmonella enterica

Authors: HAN, JING - Us Food & Drug Administration (FDA); ALJAHDALI, NESREEN - Us Food & Drug Administration (FDA); ZHAO, SHAOHUA - Us Food & Drug Administration (FDA); TANG, HAILIN - Us Food & Drug Administration (FDA); HARBOTTLE, HEATHER - Us Food & Drug Administration (FDA); HOFFMANN, MARIA - Us Food & Drug Administration (FDA); Frye, Jonathan; FOLEY, STEVEN - Us Food & Drug Administration (FDA)

Submitted to: EcoSal Plus
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2023
Publication Date: 1/4/2024
Citation: Han, J., Aljahdali, N., Zhao, S., Tang, H., Harbottle, H., Hoffmann, M., Frye, J.G., Foley, S.L. 2024. Infection biology of Salmonella enterica. EcoSal Plus. https://doi.org/10.1128/ecosalplus.esp-0001-2023.
DOI: https://doi.org/10.1128/ecosalplus.esp-0001-2023

Interpretive Summary: The aim of this review is to provide an overview of the main virulence factors and their contribution to the pathogenesis of Salmonella. Salmonella infections are the leading cause of bacterial foodborne illness in the United States and is a major health issue globally. Salmonella can cause a number of different disease syndromes, including gastroenteritis, bacteremia and enteric fever, with the most common one being gastroenteritis, characterized by abdominal pain, nausea, vomiting, diarrhea and headache. Typically, the disease is self-limiting, and most people recover without specific treatment. However, with more severe symptoms, such as bacteremia, antibiotics are used to treat the infection. Currently, there are over 2,600 serotypes of Salmonella, but not all Salmonella enterica serovars cause the same disease. Salmonella serovars differ significantly in the range of hosts they can infect, some S. enterica serovars are host-restricted and others infect a wide range of hosts. Also, they vary considerably in the nature of disease that may result, some serovars are more likely to cause invasive disease in humans and some only cause mild gastroenteritis. These clinical differences may be caused by the genetic make-up and diversity of the serovars. Salmonella virulence is very complex as lots of genes are involved in contributing to virulence. Different virulence genes play different roles in Salmonella pathogenesis. Some genes are involved in colonization of the host and evasion of the host immune system; some play roles in the survival and replication of Salmonella in the host, while some genes are involved in production of molecules that cause the clinical symptoms of the disease. Genetic analysis indicates that each clinical syndrome requires distinct sets of virulence genes, and Salmonella isolates differ in their constellation of these virulence traits. On the chromosome, virulence genes are located in clusters, which are known as Salmonella pathogenicity islands (SPIs). These SPIs are scattered throughout the different Salmonella genomes and encode factors essential for adhesion, invasion, replication and survival of Salmonella inside the host. Plasmids are also known to harbor virulence factors that contribute to Salmonella pathogenicity and severity of disease.

Technical Abstract: Salmonella enterica is the leading cause of bacterial foodborne illness in the USA, with an estimated 95% of salmonellosis cases due to the consumption of contaminated food products. Salmonella can cause several different disease syndromes, with the most common being gastroenteritis, followed by bacteremia and typhoid fever. Among the over 2,600 currently identified serotypes/serovars, some are mostly host-restricted and host-adapted, while the majority of serotypes can infect a broader range of host species and are associated with causing both livestock and human disease. Salmonella serotypes and strains within serovars can vary considerably in the severity of disease that may result from infection, with some serovars that are more highly associated with invasive disease in humans, while others predominantly cause mild gastroenteritis. These observed clinical differences may be caused by the genetic make-up and diversity of the serovars. Salmonella virulence systems are very complex containing several virulence-associated genes with different functions that contribute to its pathogenicity. The different clinical syndromes are associated with unique groups of virulence genes, and strains often differ in the array of virulence traits they display. On the chromosome, virulence genes are often clustered in regions known as Salmonella pathogenicity islands (SPIs), which are scattered throughout different Salmonella genomes and encode factors essential for adhesion, invasion, survival, and replication within the host. Plasmids can also carry various genes that contribute to Salmonella pathogenicity. For example, strains from several serovars associated with significant human disease, including Choleraesuis, Dublin, Enteritidis, Newport, and Typhimurium, can carry virulence plasmids with genes contributing to attachment, immune system evasion, and other roles. The goal of this comprehensive review is to provide key information on the Salmonella virulence, including the contributions of genes encoded in SPIs and plasmids during Salmonella pathogenesis.