Transcript Yersinia,pausteurella,francisella - Young Katuri

Yersinia
Pasteurella
Francisella
INTRODUCTION
The name Yersinia is given after
Alexander Yersin who discovered the
plague bacillus.
The genus Yersinia belongs to the family
Enterobacteriaceae.
The genus Yersinia contains three
medically important species
1.Y.pestis
2.Y.pseudotuberculosis
3.Y.enterocolitica
 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.
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 1.5×0.7microns in
size,with rounded ends and convex
sides,occur singly,in short chains or
in small groups.
 When stained with methylene blue it
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shows bipolar staining (safety pin
appearance)with two ends darkly stained
and central area clear.
Pleomorphism is very common.it is
characteristically enhanced in 3%Nacl.
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.
Morphology-safety pin
appearance
Culture
Nutrient Agar
Colonies are
small,delicate,transparent after 2448 hrs of incubation.
MacConkey Agar
 Colourless colonies are formed.
Blood agar
Colonies are non haemolytic and dark
brown due to absorption of haemin
pigment.
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).
Stalactite growth on ghee
broth
Biochemical reactions
 Y.pestis ferments glucose,mannitol and
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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
Urease
Indole
MR
catalase
Biochemical
reactions
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.
Y.pestis var. orientalis
Y.Pestis var. antiqua
Y.Pestis var. mediaevalis
RESISTANCE
It is destroyed by heat at 55˚c 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.
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
37˚c.
Cont…….
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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.
Cont…
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Virulent strains produce1.bacteriocin(pesticin 1)
2.fibrinolysin
3.coagulase.
Pesticin 1 inhibits strains
1.Y.pseudotuberculosis
2.Y.enterocolitica
3.E.coli
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.
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.
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.
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.
In human beings,plague occurs in 3
forms .
1.Bubonic plague
2.Pneumonic plague
3.septicemic plague.
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’.
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.
gangrene
PNEUMONIC PLAGUE
Highly infectious form of plague
involving the lungs producing
haemorrhagic pneumonia.
Transmission-droplet infection.
Cyanosis is very prominent.
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’.