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1. ROLE OF BACTERIAL
ORGANELLES IN VIRULENCE
Iqbal Danish & Summiya Akram
M.phil 1st Semester
Govt College University Faisalabad

2. Introduction
Pathogen: microorganism that is able to cause disease in
organisms
Pathogenicity:ability of pathogen to produce disease in host cell
 Virulence: capacity of microorganism to overcome the body
defenses,multifactorial trait.
 It is ability of being virulent
 Virule means poisonous
 host microbe interaction is necessary for virulency
 Virulence depends on:
 Number of infecting microorganisms
 Route of entry into body
 Response of the host immune system.

3. Microbial mechanism of
pathogensis
i Portal of entry
ii penetration or evasion of host defenses
iii damage to host cell
iv portal of exit
Key concept:
Several factors are required for a microbe to cause disease.
after
entering the host , pathogen adhere to host tissue ,
penetrate in
Host , and damage to the host tissue.

4. Virulence factors of bacteria
 Adherence/colonization:
Pilli
Motility(flagella)
Membrane proteins
 Infectious process
Toxins
Invasion factor(plasmid)
 Protection against host defenses:
Capsules
Cell wall

5. Invasion factor
 Plasmid
 Surface component that allow the bacteria to invade
host may be encoded on plasmid or chromosome
 Extrachromosomal DNA segments that carry gene for
antibiotic resistance known as R factor
 MDR plasmids increase the severity of clinical disease by
resistance to antibiotic therapy
 Gene coded virulency is also character of plasmid borne
surface antigen responsible for colonization of intestinal
mucos by E.Coli and Staph.aeurus are plasmid borne

6. Toxins
 Major group of virulence factors are bacterial
toxins,chemicals produced by pathogens that either
harm tissues or triggers host immune responses that
cause damage
 Two types of toxins are produced by the bacteria
 Endotoxins
 Exotoxins

7. Endotoxins
 Composed of lipid A component of gram negative bacteria
Actions of endotoxins
 Increase vascular permeability
 Initiate complement and blood coagulation cascade
 Cause fever,hypotension,disseminated intracellular
coagulation and shock

8. Exotoxins
 Secreted by gram positive and gram negative bacteria
 Encoded in bacterial chromosomal, plasmid or a phage
 Mechanism of action
 Alter cellular components
 Acts as super antigens that cause inappropriate release of
cytokines
 Inhibit protein synthesis
 Nerve impulse transmission

9. Adherence factors as virulence
factor
pilli or fimbriae
 Adhesions made of protein and antigenic nature
structure that enables the microbes to attach themselves
to host
 Microbes form colonies in mucosal site using pilli to
adhere to the cells
 Pilli is not the organ of locomotion- piliated bacteria
tends to stick to one another and produce coherent
pellicles on the surface

10. Flagella as a virulent factor
 Flagellated bacteria is more virulent than non flagellated
bacteria
 Motility towards the host cell is for adhesion and invasion
 Colonization by bacterial motility
 Flagella is composed of 20 types of proteins

11. Membrane protein
 Siderophore are iron binding factors that allow some
bacteria to compete with the host for iron,which is bound
to heamoglobin,transferin and lactoferin
 Siderophores are excreted by bacteria into the
enviroment,bind iron and thin re enter the cell

12. capsule
 Polysaccharide structure play role in bacterial
pathogenesis by promoting attachment, virulence.
 Important role of capsule
attachment of bacteria to the host cells and tissue
Protect bacteria against host defense systems
 How capsulated bacteria bacteria inhibit phagocytosis?
Bacterial capsule form micro molecules which are difficult
to phagocytosed by macrophages

13. Cell wall
 Cell wall contain virulence substances e.g. streptococcus
pyogens produces heat and acid resistance proteins
called M protein.
 M protein attach bacterium to epithelial cells of the host
and helps bacteria to resist phagocytosis by white blood
cells.
 In this way increases virulence of the microorganisms.