Persistent Infection and Long-Term Carriage of Typhoidal and Nontyphoidal Salmonellae

Abstract

SUMMARY The ability of pathogenic bacteria to affect higher organisms and cause disease is one of the most dramatic properties of microorganisms. Some pathogens can establish transient colonization only, but others are capable of infecting their host for many years or even for a lifetime. Long-term infection is called persistence, and this phenotype is fundamental for the biology of important human pathogens, including Helicobacter pylori, Mycobacterium tuberculosis, and Salmonella enterica. Both typhoidal and nontyphoidal serovars of the species Salmonella enterica can cause persistent infection in humans; however, as these two Salmonella groups cause clinically distinct diseases, the characteristics of their persistent infections in humans differ significantly. Here, following a general summary of Salmonella pathogenicity, host specificity, epidemiology, and laboratory diagnosis, I review the current knowledge about Salmonella persistence and discuss the relevant epidemiology of persistence (including carrier rate, duration of shedding, and host and pathogen risk factors), the host response to Salmonella persistence, Salmonella genes involved in this lifestyle, as well as genetic and phenotypic changes acquired during prolonged infection within the host. Additionally, I highlight differences between the persistence of typhoidal and nontyphoidal Salmonella strains in humans and summarize the current gaps and limitations in our understanding, diagnosis, and curing of persistent Salmonella infections.

High genetic similarity between non-typhoidal Salmonella isolated from paired blood and stool samples of children in the Democratic Republic of the Congo

“…Unlike for Salmonella Typhi the role of carriers in the transmission of NTS is unclear. NTS stool excretion has mainly been studied among patients recovering from NTS gastroenteritis in high-income countries [34,35]: median duration of stool excretion in children � 5 years old is 7 weeks, with 2.6% excreting beyond a 1 year period [35]. In older children, durations are shorter (median 3-4 weeks).…”

“…Assessing the concentration of NTS in stool samples could give an idea about its infectivity (e.g. 10 6 to 10 7 NTS organisms per gram of feces in case of NTS gastroenteritis) [34]. A difficult point will be the assessment of the infectious dose, as human challenge experiments typically address adult patients whereas children have the highest risk for NTS BSI [42,45].…”

Evaluation of the Safety and Protection Efficacy of spiC and nmpC or rfaL Deletion Mutants of Salmonella Enteritidis as Live Vaccine Candidates for Poultry Non-Typhoidal Salmonellosis

“…To eradicate intracellular Salmonella, it is critical to stimulate cellular immune responses in the immunized animals [39,40]. At the acute infection stage, the Salmonella-infected host can produce both Th1 and Th2 immune responses to diminish the growth of the invading bacteria, but in the second stage of persistent infection, the reduced Th1 response disrupts the balance between Th1 and Th2, and a new equilibrium between the host and persistent Salmonella infection is developed and continues [41]. Both mutants in this study can induce increased IFN-γ and IL-6 secretion from 7 to 21 days post-immunization, indicating that a prolonged Th1 immune response can be induced by these mutants.…”

Synchronous Acute Acalculous Cholecystitis and Appendicitis Due to Salmonella Group D: A Rare Case Report From China and Review of the Literature

“…Clinical symptoms associated with acute gastroenteritis caused by NTS infections are often indistinguishable from those caused by other enteric bacterial pathogens, and gold standard for diagnosis still requires isolation of the pathogen from stool samples. The pathogen may also be isolated from the blood, lymph nodes, bone marrow, and other systemic sites (10).…”