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Division of Foodborne, Waterborne, and Enviromental Diseases

Overview of Salmonella Taxonomy and Serotype Designation . Patricia Fields PhD

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Division of Foodborne, Waterborne, and Enviromental Diseases

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  1. Overview of Salmonella Taxonomy and Serotype Designation Patricia Fields PhD Team Lead, National Enteric Diseases Reference LaboratoriesEnteric Diseases Laboratory BranchAssociate Director for Laboratory ScienceDivision of Foodborne, Waterborne, and Environmental DiseasesNCEZID/CDCJanuary 26, 2012 Division of Foodborne, Waterborne, and Enviromental Diseases National Center for Emerging and Zoonotic Infectious Diseases

  2. Subtypes • Definition: Characterization of a organism or strain below a “diagnostic” level (e.g., genus-species), typically for epidemiologic purposes • Surveillance, monitoring of trends • Outbreak investigations • Etc • Examples of subtyping methods • Serotyping, biotyping, phage typing • PFGE, MLVA (DNA based “fingerprinting”) • Virulence profiling • Same subtype? Strains may be relatedDifferent subtypes? Strains likely not related • Different “subtypes” typically have only epidemiologic importance, no role in patient management

  3. CDC’s foodborne disease surveillance systems are all based on subtype • PulseNet • Based PFGE pattern = a “DNA fingerprint” • Also tracks by serotype • LEDS (Laboratory-based Enteric Disease Surveillance) • Formerly PHLIS • Passive surveillance • Based on serotype • FoodNet • Active surveillance • Based on serotype • NARMS • Surveillance for antimicrobial resistance • Also tracks by serotype

  4. Salmonella Taxonomy • Two species • Salmonella enterica • Salmonella bongori • S. enterica is further divided into six subspecies* * A 7th, unnamed subspecies is recognized genetically

  5. SalmonellaTaxonomy (cont) Salmonella enterica subspecies I Salmonella enterica subspecies VI * Subspecies IIIa and subspecies IIIb were formerly know as Genus “Arizona” Salmonella enterica subspecies II * Salmonella enterica subspecies IIIb Salmonella enterica subspecies IV Salmonella enterica subspecies VII * Salmonella enterica subspecies IIIa Salmonella bongori E. coli Adapted from McQuiston et al 2008. J. Bacteriology 190:7060-7067

  6. What is serotyping? • A subtyping method • Phenotypic characterization of strains based on immunologic reactivity of two surface structures: • Lipopolysaccharide (O antigen) • Flagellin protein (H antigen) • Serotyping schemes have been described for many different organisms • In Salmonella, includes species and subspecies identification • Horizontal gene transfer is common in Salmonella • Isolates of different subspecies can have the same O and H antigens • Salmonella serotypes are designated according to the Kauffmann-White Scheme • 2500+ serotypes

  7. 4 5 12 LPS Flagella i i 4 Salmonella serotype Typhimurium I 4,5,12:i:1,2 i 12 i i 5 Schematic Representation of Salmonella Serotype Antigens O antigen H antigen

  8. Salmonella O antigen • Outermost portion of lipopolysaccharide (LPS) • Carbohydrate antigen • Different sugars and different linkages between sugars produce the different antigens O antigen

  9. Salmonella O Antigens (cont) • Two types • O Group antigens • “Ancillary” O antigens • O Group antigens • Most important for determining serotype • rfb region contains genes responsible for O group • Found in all Enterobacteriacae • Ancillary O antigens • Typically encoded by extra-chromosomal elements (bacteriophages, plasmids) • Found in specific O groups of Salmonella • Most can vary within a given serotype, so are less important for serotype determination

  10. Salmonella O Serogroups • 46 O serogroups • O groups initially designated by capital letters • Ran out of letters … started using numbers • Now, all O Groups are designated by numbers • Letter designations still commonly used These O groups represent about 97% of human isolates

  11. Salmonella H antigens • Flagellin, the flagellar filament • A protein antigen • Variation in the middle, surface-exposed portion of the protein • Salmonella is unique in commonlyhaving two different H antigens: • Phase 1 and Phase 2 • Phase 1 has a homolog in other enterics • Phase 2 gene located in a Salmonella-specific region of the genome • The two flagellins are coordinately expressed, one is off when other is on • Monophasic: the state of having or expressing only one flagellar antigen, vs “diphasic” • “Naturally-occurring” monophasic serotypes • Subspecies IIIa, IV, and Salmonella bongori • Specific serotypes within other subspecies, e.g., Enteritidis, Typhi

  12. H Antigen Designations • 119 H antigens (Phase 1 and Phase 2) • H antigens can be: • A single epitope (e.g., a, b, c, d) • Multiple epitopes (e.g., 1,2; g,m; e,n,x) • Some H antigens are antigenically related = Complexes • One common epitope, one or more secondary epitopes • 1 complex: 1,2; 1,5; 1,6; 1,7, etc. • G complex: g,m; g,m,s; f,g,t; f,g,s; etc • H antigens typically designated by lower case letters • a; b; c; d; e,h; e,n,x; g,m; etc • 1,2; 1,5; 1,7; et al are the notable exceptions • Ran out of letters … started using numbered z’s • z4, z6, z10, z15, … z91 • Typically, no antigenic relationships between “z” antigens

  13. Designation of Salmonella Serotypes • Designated according to the conventions of the Kauffmann-White Scheme • Started with about 20 serotypes in 1934 • 2,579 serotypes in 2007 • 10-20 new recognized serotypes each year • Confirmed at CDC and Institut Pasteur • Subspecies I serotypes: submitting lab gets to name the serotype • Kauffmann-White Scheme is maintained by Institut Pasteur • Grimont and Weill, 2007. Antigenic Formulas of the Salmonella Serovars, 9th edition. Institut Pasteur, Paris, France.

  14. I 4, [5], 12 : i : 1,2 Subspecies O antigen Phase 1 Phase 2 H antigens I 4,5,12:i:1,2 I 4,12:i:1,2 serotype Typhimurium var. O5 - Subspecies I serotypes are designated by a name and a formula Salmonella enterica ser. Typhimurium “Group O:4” or “Group B” “[5]” means O antigen 5 may or may not be present.

  15. “Group O:48” or “Group Y” IV 48 : g,z51 : - Subspecies O Phase 1 “monophasic” Antigen H antigens Subspecies II through VI serotypes are designated by formula only

  16. Serotype Designations in Other Enteric Pathogens • Note: There is no compendium of recognized serotypes for E. coli; all O and H antigen combinations are acceptable, though unusual combinations should be confirmed in a reference lab. * Serotype nomenclature for Shigella was modified to fit the Salmonella and E. coli conventions

  17. Additional Resources • Good overview of history of Salmonella taxonomy and nomenclature • http://www.bacterio.cict.fr/salmonellanom.html • http://www.bacterio.cict.fr/s/salmonella.html • Kauffmann White Scheme, 9thEdition (2007) • http://www.pasteur.fr/ip/portal/action/WebdriveActionEvent/oid/01s-000036-089

  18. Thank you ! Patti Fields pif1@cdc.gov • The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention. National Center for Emerging and Zoonotic Infectious Diseases Division of Foodborne, Waterborne, and Environmental Diseases

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