Division of Foodborne, Waterborne, and Enviromental DiseasesNational Center for Emerging and Zoonotic Infectious Diseases

Overview of Salmonella Taxonomy and Serotype

Designation

Patricia Fields PhDTeam Lead, National Enteric Diseases Reference LaboratoriesEnteric Diseases Laboratory BranchAssociate Director for Laboratory ScienceDivision of Foodborne, Waterborne, and Environmental DiseasesNCEZID/CDCJanuary 26, 2012

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

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

Salmonella Taxonomy Two species

Salmonella enterica Salmonella bongori

S. enterica is further divided into six subspecies*

* A 7th, unnamed subspecies is recognized genetically

Abbreviation Taxonomic Name

I S. enterica subspecies enterica

II S. enterica subspecies salamae

IIIa S. enterica subspecies arizonae

IIIb S. enterica subspecies diarizonae

IV S. enterica subspecies houtenae

VI S. enterica subspecies indica

* Subspecies IIIa and subspecies IIIb were formerly know as Genus “Arizona”

Adapted from McQuiston et al 2008. J. Bacteriology 190:7060-7067

Salmonella Taxonomy (cont)Salmonella enterica subspecies I

Salmonella enterica subspecies VI

Salmonella enterica subspecies II

Salmonella enterica subspecies IIIb

Salmonella enterica subspecies IV

Salmonella enterica subspecies VII

Salmonella enterica subspecies IIIa

Salmonella bongori

E. coli

*

*

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

Schematic Representation of Salmonella Serotype Antigens

H antigen

i

i

45 12

i

i

Salmonella serotype TyphimuriumI 4,5,12:i:1,2

FlagellaiLPS

4

12

5

O antigen

Salmonella O antigen Outermost portion of lipopolysaccharide

(LPS)

Carbohydrate antigen Different sugars and different linkages

between sugars produce the different antigens

O antigen

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

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

O Group (number

designation)

O Group (letter

designation)Typical

O antigens2 A 2,124 B 4,127 C1 6,78 C2 6,89 D1 9,12

3,10 E1 3,1013 G 13

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

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

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.

Subspecies I serotypes are designated by a name and a

formulaSalmonella enterica ser. Typhimurium“Group O:4” or “Group B”

Subspecies O antigen Phase 1 Phase 2 H antigens

I 4, [5], 12 : i : 1,2

serotype Typhimurium var. O5 -

I 4,5,12:i:1,2I 4,12:i:1,2

“[5]” means O antigen 5 may or may not be present.

Subspecies II through VI serotypes are designated by formula only

“Group O:48” or “Group Y”

IV 48 : g,z51 : -

Subspecies O Phase 1 “monophasic” Antigen H antigens

Serotype Designations in Other Enteric Pathogens

Category Salmonella E. coli Shigella* O Groups 46 181 44 Ancillary O antigens 13 none yes H antigens 115 56 none Recognized serotypes 2,579 na 50

* Serotype nomenclature for Shigella was modified to fit the Salmonella and E. coli conventions

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.

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, 9th Edition (2007) http://

www.pasteur.fr/ip/portal/action/WebdriveActionEvent/oid/01s-000036-089

For more information please contact Centers for Disease Control and Prevention1600 Clifton Road NE, Atlanta, GA 30333Telephone, 1-800-CDC-INFO (232-4636)/TTY: 1-888-232-6348E-mail: cdcinfo@cdc.gov Web: www.cdc.gov

Thank you !Patti Fields

pif1@cdc.gov

National Center for Emerging and Zoonotic Infectious DiseasesDivision of Foodborne, Waterborne, and Environmental Diseases

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.