Salmonella on xld1/16/2024 ![]() ![]() enterica strains constitute the majority (as much as 99.5%) of isolates cultured from humans and other warm-blooded animals, it is perhaps not surprising that the majority of disease causing serovars belong to this subspecies. 21 The resolution provided by serologic typing methods has proved valuable to epidemiologic tracking of isolates in outbreaks. The serologic typing scheme identifies >2500 serovars. The seven principle members of the Salmonella genus can be further subtyped by serologic methods, based on three antigens: O, H, and Vi. There are greater than 2500 serovars in total, with the most common disease-causing serovars belonging to S. Only the most common typhyoidal serovars, and representative non-typhoidal serovars are shown. Four representative serovars are shown for S. Note that serovars do not have official taxonomic status. Relationships within the Salmonella genus, including species, subspecies, and serovar designations are illustrated. 5 Following hematogenous dissemination, some individuals will develop typhoid fever, which involves high temperature (>39° C), vomiting, and headache, sometimes with complications that include neurologic involvement, intestinal perforation and death. After invading through intestinal mucosa, typhoidal strains disseminate through a transient primary bacteremia that may occur without diarrhea. In contrast to infection with non-typhoidal Salmonella, infection with typhoidal strains (primarily serovars Typhi and Paratyphi) presents as a systemic, often serious, disease. Though this is more common in those with compromised immune systems or underlying medical conditions (e.g., sickle cell anemia), systemic spread of non-typhoidal Salmonella strains may be seen in otherwise healthy individuals as well. 7 In most cases in healthy individuals, this infection runs a self-limited course over 4–7 days but, in susceptible hosts, certain non-typhoidal strains of Salmonella may spread systemically to other sites in the body. Infection with non-typhoidal serovars ordinarily presents as diarrhea associated with fever and abdominal cramping 12–72 hours after infection. Infection with Salmonella typically follows two very different disease courses, depending on whether the infecting Salmonella strain is a typhoidal or non-typhoidal serovar. 6 However, classical biochemical testing alone does not unambiguously distinguish key pathogenic members of this genus and modern classification relies instead on serology and increasingly on molecular methods. Salmonella is a member of the Enterobacteriaceae, originally characterized by their ability to metabolize citrate as a sole carbon source and lysine as a nitrogen source, as well as their ability to produce hydrogen sulfide. 1– 3 Though relatively uncommon in the U.S., typhoid, paratyphoid, and enteric fever constitute a very serious global public health problem, with 25 million new infections and >200,000 deaths occurring annually. In the developed world, food-borne acute gastroenteritis and enterocolitis are the most common forms of Salmonella infection, with an estimated 1.2 million annual cases of non-typhoidal Salmonellosis occurring in the U.S. Members of the genus Salmonella cause a well-characterized spectrum of disease in humans, ranging from asymptomatic carriage to fatal typhoidal fever. Throughout, priority of discussion is placed on newer techniques and data, with less emphasis on details of classical methods available in reference textbooks. ![]() Topics common to all three (such as collection, transport and storage of specimens, and molecular multiplex methods of detection) are discussed as they first occur, denoted as such in paragraph headings. Discussions that pertain to individual organisms are organized into individual sections starting with Salmonella, followed by Shigella, then Yersinia. In this review, we cover infection and epidemiology, taxonomic classification, collection, transport, and storage of specimens, culture techniques, molecular detection methods, susceptibility testing, and treatment. ![]() These important members of Enterobacteriaceae are responsible for significant morbidity and mortality, causing diarrhea and a spectrum of associated symptoms from mild to severe in most parts of the world. In this review, we discuss three enteric pathogens: Salmonella, Shigella, and Yersinia. ![]()
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