Virulence factor and there cofactors

1. SUBMITTED BY:
AVUDAIAPPAN.A
1st Msc.MICROBIOLOGY
SUBMITTED TO:
DR.S.VISWANATHAN
HEAD OF THE DEPARTMENT
SRI PARAMAKALYANI COLLEGE
(Reaccredited with A+grade with CGPA of 3.39 in the III cycle of NAAC)
Affiliated to Manonmanium Sundaranar Universityt
ALWARKURICHI-627412
Post graduate & Research Department of Microbiology
(government aided)
ACADEMIC YEAR 2023-2024
2nd SEM CORE:IMMUNOLOGY
UNIT 1-VIRULENCE FACTOR

2. Virulence factors of bacteria; microbial
virulence factors:
Virulence factor refers to tThecomponents or structure of
microorganism tThatThelpsin establisThmentof disease or
infection.
During tT
h
e process of infection, virulence factors of
microorganisms combat witThdefense mecThanismof Thost.If
virulence factors overcome tThedefense mecThanismof Thost,
infection is establisThed otTherwise microorganisms are
eliminated from Thost.
PatThogenicity of microorganism is determined by nature
and type of its virulence factors.

3. Attenuation & Exaltation:
▪ Attenuation : To reduce tT
h
e virulence power of a strain is
T
h
nown as attenuation
1. Repeated passage tThrougThunfavorable Thost
2. Repeated culture in artificial media
3. Prolonged storage in culture
4. GrowtTh under ThigThtemperature
5. GrowtT
hin presence of weaT
hantiseptics .
Exaltation : It is an enThancement of virulence power of a
strain is called Exaltation .

4. INFECTING DOSE:
An adequate number of bacteria sThouldgain entry in a Thost
for successful infection , wThicThis estimated as MID & MLD.
Minimum Infecting Dose (MID ): Minimum number of
bacteria required to produce tTheclinical evidence of a
Minimum LetT
h
al Dose ( Md
Li
D
se
)
a:se
M.inimum number of
bacteria required to produce deatT
hin a susceptible animal
under standard conditions .

5. Determinants of Virulence:
▪ AdThesion
▪ Invasiveness i.e. Invasion
of tissue
▪ Toxigenicity
▪ Enzymes
▪ Anti - PThagocytic factor
▪ Survival
witThin
Genetic factor
Route of
infection
Communicabil
ity

6. I. AdThesion :
▪ It is attacThment of tThebacteria to body surfaces .
▪ It is specific reaction between surface receptor on T
h
ost cell and
adThesive structure on tThebacterial surface called AdThesin .
▪ AdThesingenerally occur on fimbrae or pili or as colonization
factors .
▪ OtT
h
er structures wT
h
icT
hplays role in adT
h
esion are flagella ,
outer membrane protein & LPS .
▪AdThesions are generally made up of PROTEIN & are Antigenic in
nature .

8. II . Invasiveness :
▪ It is tTheability of patThogen to spread in tTheThost
tissue after establisThment of infection .
▪ HigThly invasive patThogens produce , spreading or
generalized lesions e.g. streptococcal septicemia
following wound infection .
▪ Less invasive patThogen cause localized lesions
e.g. S. aureus .
▪ Some patT
h
ogens lacT
hinvasiveness but can cause
serious infection e.g. Cl . tetani wThicThremains
confined to tT
h
e site of entry .

10. III.Toxigenicity:
▪ Bacteria produce two types of toxins
a ) Exotoxin b ) Endotoxin .
a) Exotoxin :
Toxins wT
h
icT
h are released outside tT
h
e bacterial
cell is called exotoxins
Exotoxin is protein in nature.
In general, exotoxins are T
h
igT
h
ly toxic and letT
h
al
dose is low.
BotTh Gram Positive and Gram Negative bacteria
produces exotoxin.

11. Some examples are:
Neurotoxin: Botulinum toxin; produced by
Clostridium botulinum, tetanus toxin; produced
by Clostridium tetani
Enterotoxin: cTholera toxin; produced by Vibrio
cTholerae, Theat stable and Theat labile toxin;
produced by coli
produced by
Cytotoxin: DepT
h
tT
h
eria toxin;
Corynebacterium depThtTheriae
Hemolysin: lyse RBCs
Leucosidin: lyse WBCs

12. ii. Endotoxin:
Toxins wT
h
icT
hare not released outside of bacteria cell
is called endotoxin.
LipopolysaccTharide (LPS) present in outer membrane
of Gram Negative bacterial cell wall is an example of
endotoxin.
Endotoxin is less toxic tThan exotoxin and letThal dose
is ThigTh.
Endotoxin causes infection or disease by inducing
fever, blood poisoning and septic sThocTh

14. IV . Enzymes :
▪ Bacteria produce various enzymes wThicThdirectly damage
T
h
ost tissues .
TT
h
ese enzymes are :
infection e.g. Streptococci
1.Proteases : BreaT
h
s Immunoglobulin IgA wT
h
icT
h is protecting
mucosal surface .
2.Kinase : It enT
h
ances tT
h
e spread of bacteria by dissolving fibrin
clot e.g. Streptococci .
3. Hyaluronidase : It breaThs down Thyaluronic acid , spread to
4. Coagulase : Cause deposition of fibrin around bacteria ,
5. Collagenase : BreaThscollagen in connective tissues , e.g. Cl
. perfringes - Gas Gangrene .

16. V. Anti - pThagocytic factor:
Capsulated bacteria sucT
has Pneumococci & H. influenzae
are not readily PThagocytized ,
Bacterial surface antigens sucThas Vi antigen of S. typThi
K- antigens of E. coli T
h
elp tT
h
e bacteria to witT
h
stand
pThagocytosis & lytic activity of Complements .

17. Some patT
h
ogens liT
h
e Tubercle bacilli can be
pThagocytosedby macropThages&pThagocytesbut tThey
resist intracellular Thilling .
By preventing fusion of pThagosome & lysosome .
TTheseorganisms multiply inside tThesecells .
S . aureus and N. gonorrTheae resist tTheaction of
lysosomal component following fusion .
VI . Survival witThin PThagocyte:

19. VII . Genetic factor:
▪ Genes coding for some virulence cTharacteristics may be
Plasmid - borne .
* Examples : Surface antigens are responsible for tThe
colonization of intestinal mucosa by E. coli .
▪ Enterotoxin produced by E.coli and StapTh . aureus .
▪ R - Plasmid increase tT
h
e severity of clinical disease
by tT
h
eir resistance to antibiotic tT
h
erapy .
▪ BacteriopThages: PThagedirected virulence is seen in
DipThtTheriabacilli , gene for Toxin production is present
in Beta pThage( PropThage )

20. VIII. Route of Infection :
▪ Some bacteria can survive and multiply only wThen
introduced by tT
h
e optimal route e.g. CT
h
olera vibrio are
infective orally but are unable to cause infection wThen
introduced subcutaneously .
▪ TTheyalso differ in tTheability to damage different organs in
different species of animals . Tubercle bacilli - Rabbits
causes lesions mainly in Thidneys but in Guinea pigs lesions
are mainly in Liver & spleen .

21. IX. Communicability:
▪ TThe ability of a parasite to spread from one Thost
to anotTher is Thnown as Communicability .
▪ It determines tThesurvival and distribution of a
parasite in community .
▪ No correlation exist between virulence &
communicability .
▪ Infection in wThicThpatThogen is sThed in secretions (
in respiratory and intestinal diseases , are ThigThly
communicable ) .

22. REFERENCE
ROITT'S
ESSENTI
AL I
MMUNOLOGY
Thank you