Yersinia,pausteurella,francisella - Young Katuri
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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
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
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…….
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…
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’.