Salmonella enterica belongs to non-typhoid salmonellae and is a gram-negative rod, facultative anaerobic, flagellate. It can be found in many species of animals and is a zoonotic pathogen.
Salmonella is divided into two groups: (1) Typhoidal Salmonella, which is made up of bacterial strains that cause typhoid fever or paratyphoid fever, and both of them are mandatory communicable disease. (2) Non-typhoidal Salmonella, which includes all other Salmonella strains and are more common. The clinical symptoms of Non-typhoidal Salmonella are different among each serotypes, from asymptomatic carrier to bacteremia. Children, elderly persons and patients with immunosuppressive therapy are at higher risk. The major routes of Salmonella enterica transmission are through eggs, food animals and meat. Most of the infections are caused by eating the fecal contaminated water or foods and seldom are caused by contacting pets.
The bacterial genus Salmonella is divided into two species, Salmonella bongori and S. enterica. S. enterica itself is comprised of six subspecies: they are S. enterica subsp. enterica、S. enterica subsp.salamae、S. enterica subsp. arizonae、S. enterica subsp. diarizonae、S. enterica subsp. houtenae、S. enterica subsp. Indica. The Kauffmann–White classification is a system that classifies the genus Salmonella into serotypes, based on surface antigens. Salmonella have very complicated antigen structures and can be divided into three categories: Somatic O antigen, Flagellar H antigen and Capsular Vi antigen. There are over 2000 serovars for S. enterica.
Nowadays, we can use molecular bio-analysis to identify more than 2600 serotypes for Salmonella. While there are a range of methods available for strain characterization and subtyping, the most commonly used methods include Pulse Field Gel Electrophoresis (PFGE), Multi-Locus Sequence Type (MLST) analysis, and Whole genome sequence (WGS). PFGE is the current gold standard fingerprinting method to compare genetic variance and often used by Centers for Disease Control and Prevention (CDC) and United States Department of Agriculture (USDA) to analyze the zoonotic pathogen.
Continuous genetic and genomic evolution in Salmonella leading to increased virulence and resistance to multiple drugs are of significant public health concern. Emergence of foodborne human infections caused by Salmonella enterica serotype Enteriditis and by multidrug-resistant strains of Salmonella enterica serotype Typhimurium occurred in the 20th century.
Reference:
Stepan RM, Sherwood JS, Petermann SR, Logue CM. Molecular and comparative analysis of Salmonella enterica Senftenberg from humans and animals using PFGE, MLST and NARMS. BMC Microbiol 11: 153, 2011.
Ranieri ML, Shi C, Moreno Switt AI, den Bakker HC, Wiedmann M. Comparison of typing methods with a new procedure based on sequence characterization for Salmonella serovar prediction. J Clin Microbiol 51: 1786-1797, 2013.
Swaminathan B, Barrett TJ, Hunter SB, et al. PulseNet: the molecular subtyping network for foodborne bacterial disease surveillance, United States. Emerg Infect Dis 2001; 7: 382–9.
臨床微生物學: 細菌與黴菌學。作者：吳雪霞，周以正， 周如文， 胡文熙，洪貴香，張長泉，張益銍，張誌，孫培倫，彭健芳，黃小萍，廖淑貞，禇佩瑜，鄧麗珍，謝素娥，蘇玲慧