Yersinia

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• Yersinia
• Pasteurella
• Francisella

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INTRODUCTION

• The name Yersinia is given after Alexander Yersin
  who discovered the plague bacillus.
• The genus Yersinia belongs to the family
  Enterobacteriaceae.

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• The genus Yersinia contains three medically
  important species 1.Y.pestis
  2.Y.pseudotuberculosis 3.Y.enterocolitica

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• The genus pasteurella contains several related
  bacteria causing hemorrhagic septicaemia
  in different species of animals and occasionally
  producing human infections.
• The genus francisella consisting of F.tularensis
  is named after Francis for his contribution on
  tularaemia,caused by this bacillus.

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YERSINIA PESTIS

• Causative agent of plague formerly known as
  pasteurella pestis was isolated independently and
  simultaneously by Yersin and Kitasato
• MORPHOLOGY
• short ovoid,gram negative bacillus,about
  1.50.7microns in size,with rounded ends and
  convex sides,occur singly,in short chains or in
  small groups.

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• When stained with methylene blue it shows bipolar
  staining (safety pin appearance)with two ends
  darkly stained and central area clear.
• Pleomorphism is very common.it is
  characteristically enhanced in 3Nacl.
• In old cultures involution forms coccoid,club
  shaped,filamentous and giant forms are observed.
• The bacterial body is surrounded by a slime layer
  (envelope or capsule).
• It is non motile,non sporing and non acid fast.

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Morphology-safety pin appearance
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Culture

• Nutrient Agar
• Colonies are small,delicate,transparent after
  24-48 hrs of incubation.
• MacConkey Agar
• Colourless colonies are formed.

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Blood agar

• Colonies are non haemolytic and dark brown due to
  absorption of haemin pigment.

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• Broth
• In nutrient broth,a flocculent growth occurs at
  bottom and along sides of tube.
• Ghee broth
• A characteristic growth occurs which hangs down
  from surface resembling stalactites(Stalactite
  growth).

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Stalactite growth on ghee broth
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Biochemical reactions

• Y.pestis ferments glucose,mannitol and maltose
  with production of acid but no gas.
• Lactose and sucrose are not fermented.
• Catalase-positive
• Urease-negative
• Indole-negative
• MR-positive
• Vp-negative
• Citrate-negative

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Biochemical reactions
Urease Indole MR catalase
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• On the basis of fermentation of glycerol and
  redution of nitrate,Devignat distinguished 3
  physiological varieties.
• This is of epidemiological significance because
  of different geographical distribution.

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• Y.pestis var. orientalis
• Y.Pestis var. antiqua
• Y.Pestis var. mediaevalis

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RESISTANCE

• It is destroyed by heat at 55c in 15 min and
  also by sunlight,drying and 0.5 phenol in 15
  min.
• Survive for several months in soil of rodent
  burrows.
• Remains viable for long periods in cold and moist
  environments.

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ANTIGENIC STRUCTURE

• These are antigenically homogenous and serotypes
  do not exist.
• The antigenic structure is complex and about 20
  diff antigens have been identified.They include
• A heat labile protien envelope antigen known as
  fraction-I,best formed in cultures incubated at
  37c.

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Cont.

• Fraction-I inhibits phagocytosis.
• It is present only in virulent strains.
• It has imp role in stimulating protective
  immunity in mice and man.
• V and W proteins which are also formed by
  virulent strains have been considered to be
  virulence factors as they inhibit phagocytosis.

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Cont

• Virulent strains produce-
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  1.bacteriocin(pesticin 1)
• 2.fibrinolysin
• 3.coagulase.
• Pesticin 1 inhibits strains
• 1.Y.pseudotuberculosis
• 2.Y.enterocolitica
• 3.E.coli

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• Plague toxins-refers to atleast 2 classes of
  toxins found in culture filtrates.
• First is the endotoxin,a liposaccharide similar
  to endotoxin of enteric bacilli.
• Second possess properties of both exotoxins and
  endotoxins.

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• Also called murine toxins as they are active in
  mice and rats but not in guinea pigs,rabbits and
  primates.
• On injection,into exp animals these produce local
  edema and necrosis with systemic effects on
  peripheral vascular sys. and liver.

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• Virulence also appears to be associated with an
  unidentified surface component which absorbs
  haemin and basic aromatic dyes in culture media
  to form coloured colonies.
• Virulence has also been associated with the
  ability to synthesize purines.

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Pathogenesis

• Y.pestis is a natural pathogen of rodents and
  causes zoonotic disease called plague.
• It is transmitted to man via the bite of
  infected rat flea.(X.cheopis).
• The incubation period is 2-6 days.
• Two natural cycles of plague exist
• 1.URBAN PLAGUE
• 2.WILD OR SYLVATIC PLAGUE.

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• In human beings,plague occurs in 3 forms .
• 1.Bubonic plague
• 2.Pneumonic plague
• 3.septicemic plague.

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• BUBONIC PLAGUE
• After an incubation period of 2-5 days,lymph
  nodes infected.
• As bacillus usually enters through bite on
  legs,inguinal nodes are involved.
• Hence the name bubonic.

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• The glands become enlarged and suppurate.
• Patient develops fever,chills and malaise.
• Often bacillus reaches blood stream and gets
  widely disseminated leading to gangrene of
  skin,fingers and penis.

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gangrene
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• PNEUMONIC PLAGUE
• Highly infectious form of plague involving the
  lungs producing haemorrhagic pneumonia.
• Transmission-droplet infection.
• Cyanosis is very prominent.

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• SEPTICEMIC PLAGUE
• The presence of bacteria in blood.
• Usually the terminal event in bubonic or
  pneumonic plague.
• Massive involvement of blood vessels results in
  haemorrhages in skin and mucosa.so, the disease
  is given the name BLACK DEATH.

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