Summary of SMI: ID 21: Yersinia

🦠 Genus Yersinia Overview

📊 Taxonomy

Family: Enterobacteriaceae
Species: 17 recognized species + 2 subspecies
Type species: Yersinia pestis
Pathogenic species: Y. pestis, Y. pseudotuberculosis, Y. enterocolitica

🧬 General Characteristics

Gram-negative, catalase-positive, oxidase-negative
Facultatively anaerobic straight rods to coccobacilli
Non-spore forming
May show bipolar staining ("closed safety-pin appearance")
Respiratory and fermentative metabolism
Optimum growth: 28-29°C
Motile at <30°C (except Y. pestis - always non-motile)
Non-motile at 37°C

🎯 Medically Important Yersinia Species

🔴 Yersinia enterocolitica (Ye)

Biotypes: 6 types (1A, 1B, 2, 3, 4, 5) with >50 serogroups
Pathogenic: Biotypes 1B (highly pathogenic) and 2-5
Non-virulent: Biotype 1A
CIN agar: Deep-red center with transparent border ("bull's-eye")
Lactose: Usually negative (some strains positive)
Urease: Positive
Indole: Variable
Motility: Yes, below 30°C

🟡 Yersinia pseudotuberculosis (Yps)

Serotypes: 15 O-serotypes (O:1-O:15) + 10 subtypes
CIN agar: Smaller, deep red with sharp border + translucent zone
Lactose: Non-fermenter
Urease: Positive
Indole: Negative
Nitrate: Reduces nitrate
Motility: Yes, below 30°C

🟣 Yersinia pestis (Yp)

Growth: Not fastidious, grows well on blood agar
24h colonies: Small grey-white, translucent
48h colonies: Grey-white to yellow, opaque
Morphology: "Fried egg" or "hammered copper" appearance
Broth: Produces "stalactites" in nutrient-rich broth
Indole: Negative
Urease: Negative
Lactose: Negative
Motility: Non-motile

🔍 Species Comparison Table

Test	Y. enterocolitica	Y. pseudotuberculosis	Y. pestis
Indole	Variable	Negative	Negative
Urease	Positive	Positive	Negative
Lactose fermentation	No (some strains positive)	No	No
Motility	Yes, below 30°C	Yes, below 30°C	No
Catalase	Positive	Positive	Positive
Oxidase	Negative	Negative	Negative

🔬 Laboratory Process

📋 Sample Collection

Ye & Yps: Usually feces
Yp: Blood, bubo fluid, sputum, CSF, feces, urine

🧪 Primary Isolation

Media: CIN agar for Ye and Yps
Indication: Appendicitis, mesenteric lymphadenitis, terminal ileitis, reactive arthritis
Special requests: Erythema nodosum, hemochromatosis, iron chelation therapy, farming/vet/lab exposure

🔍 Identification

Colonial appearance: "Bull's eye" colony on CIN agar
Traditional: Biochemical tests (API) from non-selective media
Modern: MALDI-ToF (check up-to-date database)
Confirmation: Send to reference lab on Dorset egg agar

🧬 Molecular Methods

Multiplex PCR: Many labs use panels including Yersinia
Process: Interim result → culture for ID/sensitivity → reference lab typing
Typing methods: MLVA, PFGE, Whole Genome Sequencing

📊 Laboratory Workflow

Stool specimen with clinical details

Routine stool test + CIN agar OR Multiplex PCR

Bull's eye colony on CIN agar OR Yersinia detected

Identification by Biochemical method (API) or MALDI-ToF

Issue report + Sensitivity test + Send to reference lab

🔬 Multiplex PCR Information

Many laboratories now use multiplex PCR panels that include Yersinia detection. When identified:

Interim result is issued
Sample undergoes culture for further identification
Antimicrobial sensitivity testing performed
Sample sent to reference laboratory for typing

⚠️ Laboratory Safety

🚨 Hazard Classifications

All Yersinia species: Hazard Group 2
Yersinia pestis: Hazard Group 3

🛡️ General Safety Requirements

Laboratory procedures creating infectious aerosols must be conducted in microbiological safety cabinet
Good laboratory practice including appropriate PPE must be used
Local COSHH assessment should be followed

🔒 Y. pestis Specific Requirements

ALL work must be performed under Containment Level 3 conditions
Vaccination recommended for laboratory personnel routinely exposed to live Y. pestis
If suspected, move isolate to Category 3 room immediately
Follow appropriate infection control and good laboratory practice
All processing in Cat 3 room cabinet
Send to Porton Down for further testing
Inform UKHSA and IPC

🩸 Blood Culture Protocol

For wound swab, bubo fluid, respiratory specimen, or CSF:
• Follow SMI for respective specimen type
• If Y. pestis suspected: immediate Category 3 protocols

🧫 Culture Media

🎯 CIN Agar (Cefsulodin-Irgasan-Novobiocin)

Selective and differential medium for Yersinia isolation

🧪 Composition & Function

Peptone & yeast extract: Essential nutrients
Mannitol: Fermentable carbohydrate for differentiation
Sodium pyruvate: Enhances recovery of stressed bacteria
Sodium chloride: Maintains osmotic balance
Magnesium sulfate: Supplies necessary ions

🚫 Selective Components

Sodium deoxycholate: Bile salt suppressing Gram-positive bacteria
Crystal violet: Suppresses Gram-positive bacteria
Irgasan (triclosan): Inhibits most Gram-negative and Gram-positive organisms
Cefsulodin: Selective antibiotic
Novobiocin: Selective antibiotic

🔍 Differential Component

Neutral red: pH indicator
Turns red in acidic conditions from mannitol fermentation
Creates characteristic colony morphology
Bull's-eye appearance: red center with transparent border

🥚 Dorset Egg Media

Primary use: Cultivation and identification of Mycobacterium species, particularly M. tuberculosis

Whole eggs: Provide essential proteins, lipids, and nutrients
Glycerol: Additional carbon source enhancing mycobacterial growth
Sodium chloride: Maintains osmotic balance
Potato starch: Provides carbohydrates and neutralizes toxic metabolites
Preparation: Heat coagulation at 85°C creating solid, slanted surface
Use for Yersinia: Can be used to transfer Yersinia to reference laboratory

📋 Summary

🔬 Microscopy

Ye, Yps: Usually from blood culture or sterile specimen (CSF)
Yp: From blood culture or sterile specimen
Appearance: Gram-negative rods with possible bipolar staining

🧫 Culture

Ye, Yps: CIN agar (28-30°C for 24-48 hrs) if clinically indicated
Yp: Common media for specimen type + CIN (less useful than Ye/Yps)

🎯 Growth Characteristics

Ye, Yps: Bull's-eye colony on CIN
Yp: Small grey-white, translucent → "fried egg" or "hammered copper" appearance

🧪 CLED Results

Ye, Yps: NLF (some Ye strains may ferment lactose)
Yp: NLF

🔬 Key Tests

Urease: Ye/Yps positive, Yp negative
Motility: Ye/Yps yes (below 30°C), Yp no
Catalase/Oxidase: All catalase-positive, oxidase-negative

🏥 Identification Methods

Ye, Yps: API, MALDI-ToF, PCR (GBRU-Colindale)
Yp: API, MALDI-ToF, PCR (RIPL-Porton Downs)

Parameter	Ye, Yps	Yp
Microscopy	Usually from blood culture or sterile specimen. Gram-negative rods with possible bipolar staining
Culture	CIN agar (28-30°C for 24-48 hrs) if clinically indicated	Common media for specimen type + CIN (less useful)
Growth	Bull's-eye colony on CIN	Small grey-white, translucent → "fried egg" or "hammered copper"
CLED	NLF (some Ye strains may ferment lactose)	NLF
Urease	Positive	Negative
Motility	Yes, below 30°C	No
Catalase/Oxidase	Catalase-positive and oxidase-negative
Identification	API, MALDI-ToF, PCR (GBRU-Colindale)	API, MALDI-ToF, PCR (RIPL-Porton Downs)

🔬 Yersinia Species Identification Guide